Next Article in Journal
Bacteria Isolated from the Aeration Chamber of Wastewater Treatment Plants Used in the Biocontrol and Promotion of Wheat Growth
Next Article in Special Issue
Effects of a Salicylic Acid Analog on Aphis gossypii and Its Predator Chrysoperla carnea on Melon Plants
Previous Article in Journal
Selection of the Root Endophyte Pseudomonas brassicacearum CDVBN10 as Plant Growth Promoter for Brassica napus L. Crops
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Agronomy
Volume 10
Issue 11
10.3390/agronomy10111791
agronomy-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Review

Siliceous Natural Nanomaterials as Biorationals—Plant Protectants and Plant Health Strengtheners

by
Diana Constantinescu-Aruxandei
,
Carmen Lupu
and
Florin Oancea
*
Department of Bioresources, National Institute for Research & Development in Chemistry and Petrochemistry—ICECHIM, Splaiul Independenței nr. 202, Sector 6, 060021 Bucharest, Romania
*
Author to whom correspondence should be addressed.
Agronomy 2020, 10(11), 1791; https://doi.org/10.3390/agronomy10111791
Submission received: 22 October 2020 / Revised: 4 November 2020 / Accepted: 13 November 2020 / Published: 16 November 2020
(This article belongs to the Special Issue Biorationals as Plant Protectants and Plant Health Strengtheners)
Browse Figures
Versions Notes

Abstract

:
This review aims to evaluate the scientific evidences for siliceous natural nanomaterials (SNNMs), natural zeolites, and diatomaceous earth, as biorationals. Both SNNMs are multifaceted agricultural inputs—plant protectants, plant biostimulants/plant strengtheners, soil improvers. The effects depend on the plant parts, where such siliceous natural nanomaterials (SNNMs) are applied. For stored grains, SNNMs act as plant protectants. Foliar applied SNNMs protect plants against biotic and abiotic stress—plant protectant and plant strengtheners. When applied to soil/roots, SNNMs stimulate root development and improve soil characteristics. These effects are related to the composition and porous (nano)structure of SNNMs. The large active siliceous surfaces of SNNMs are involved in: desiccation of the insects damaging stored grains, fungistatic effects against mycotoxigenic fungi and adsorption of their mycotoxins, desiccation of foliar pathogens and pests, stimulation of photosynthesis, release of soluble silicon species, improved soil characteristics. Similar to other biorationals from the category of basic substances with low risk, the SNNMs efficacy as plant protectants and plant health strengtheners is rather low. Complementary active ingredients should be used to enhance the effects of SNNMs on treated plants. For SNNMs applied as protectants of stored seeds, such strategy, of using complementary biorationals/low risk substances, proved to be highly effective.

Graphical Abstract

1. Introduction

The siliceous natural nanomaterials (SNNMs) considered for this review, i.e., natural zeolites and diatomaceous earth/kieselguhr, are mineral natural products–volcanic ashes altered by water [1], and, respectively, biogenic sedimentary rocks [2]. Both SNNMs are generally recognized as safe (GRAS), being put on the market as dietary supplements (natural zeolites [3,4], diatomaceous earth [2,5]), feed additive (natural zeolites [6,7], diatomaceous earth [8,9,10,11]), filtration aid in beverage industry (natural zeolites [1], diatomaceous earth [12,13,14]).
Both SNNMs, natural zeolites and diatomaceous earth/kieselguhr, could be considered among biorationals categories when used in agriculture. The term “biorationals” refers to low-risk products which promote cultivated plant health [15]. Biorationals include plant protectants, plant biostimulants/plant strengtheners, and soil conditioners/soil improvers [15]. The main characteristic of biorationals is sustainability–low risk associated with lower stress impact on crop yield [15]. Their integrated use, in the frame of integrated pest management/integrated farming systems [16], is essential for a profitable agricultural production with low impact on global health.
The SNNMs considered for this review fulfill the criteria established for basic substances by Art. 23 of European Union (EU) Regulation 1107/2009 (concerning plant protection products) [17]: are safe, due to their long utilization without significant side effects; are without endocrine disrupting, neurotoxic or immunotoxic effects; and are not predominantly used as plant protection products. The products based on diatomaceous earth (under the name kieselguhr) are placed on the market as stored grain protectants [18]. This niche application is the only application connected to plant protection products–diatomaceous earth (DE) being predominantly used in the industry.
SNNMs were proved to have mainly plant strengthening effects. Such SNNM effects could be considered as being direct or indirect (mediated). Direct effects on plant physiology are related to the soluble silicon species, silicic acid, and its dimers/trimers, slowly released from diatomaceous earth [19,20] or natural zeolites into plant rhizosphere [21]. The mediated plant strengthening effects are induced by the soil/growing media improvements following the SNNMs application. SNNMs are typical soil conditioners, improving aeration and water holding capacity [22,23]. Recently, SNNMs, and especially natural zeolites, were considered solutions to emerging crops challenges, as part of geo-agriculture [24]. Two of the considered challenges addressed by geo-agriculture, i.e., environmental-sustainable fertilizers and enhanced crop drought resilience, could be considered as related to SNNMs plant strengthening effects too.
SNNMs effects related to plant protection against biotic stress, plant pathogens and pest, were reported. SNNMs products, known also as “inert dusts”, are used for decades as stored grain protectants, effective both against insects [25,26,27] and mycotoxigenic fungi [28,29]. There are also reports that demonstrate that foliar applications of siliceous natural nanomaterials protect plants against biotic stress. Diatomaceous earth sprayed onto canopy controls the population of aphids [30,31]. Similar effects, related to the control of leaves pest (leafminer Tuta absoluta), were observed for natural zeolites applied as treatment of tomato leaves [32].
The extended use of these biorationals in agriculture depends significantly on the legal status of siliceous natural nanomaterials as agricultural inputs. This legal status of biorationals– mandatory registration for plant protectants against biotic stress and variable administrative procedure before putting on the market for plant strengtheners–is different in different parts of the world. The different approaches are reflected also on SNNMs used in agriculture. SNNMs (diatomaceous earth) based products used for stored grain protection are registered as plant protection products in the European Union [18] and USA [33]. However, a different approach is for products with plant health strengthening effects.
SNNMs used for soil treatment/soil improvement do not have unitary requirement regarding registration. In most of the world countries, including USA (where these products are regulated on a state-by-state basis) soil conditioners/soil improvers are put on the market without prior registration/notification procedure. The regulations establish maximum level of contaminant and mandatory quality characteristics. The products which producers consider fulfilling the quality and safety requirements according to standards are put on the market at producer’s own responsibility–and post marketing control is done by governmental agencies. The legislation in force in EU for soil improvers, i.e., Regulation 1009/2019, establishes specific quality and safety requirements–maximum thresholds for contaminants, e.g., potential toxic elements, and requires demonstration of the claimed effects for access to the common market. However, there are still different approaches for soil improvers in different EU countries. For example, in Hungary, soil improvers are considered yield enhancers and are subject to National authorization according to decree 36/2006 of Ministry of Agriculture and Rural Development (FVM) [34].
Until, now SNNMs were not considered as plant biostimulants/plant strengtheners, despite the fact that their application as foliar treatment leads to effects specific to plant biostimulants (as it will be further discussed in this review). Plant biostimulants also have different legal status in different parts of the world. In EU, according to Regulation 1009/2019, plant biostimulants need registration [35]. The evolution toward an unitary approach of the plant biostimulants regulatory framework in different European countries (and the situation at international level) was reviewed three times during the last years by a research group from Italian CREA (Consiglio per la Ricerca in Agricoltura e l’Analisi dell’economia agraria) [35,36,37].
The objectives of this review are to evaluate the scientific evidences for SNNMs as biorationals, i.e., plant strengtheners and plant protectants with low environmental impact; to analyze the best approach for their extended implementation in sustainable farming practices and to identify knowledge gaps and needs for further investigations. Arguments regarding inclusion of SNNMs in the different categories, plant protection products, soil conditioners/improvers or plant strengtheners–dual plant biostimulants, are further considered and discussed, after a short presentation of SNNMs structure peculiarities.

2. Siliceous Natural Nanomaterials Structure

Both SNNMs are siliceous compounds, with a porous nanostructure. Natural zeolites are crystalline hydrated polymeric tecto-aluminosilicates [38]. The polymeric structure is based on monomeric tetrahedral units–TO4, where T is aluminum (Al) or silicon (Si) [1]. The monomeric tetrahedral units are linked by oxygen bridges [39]. The porous structure of natural zeolites is determined by its inorganic polymeric nature, the linked tetrahedron generating a nanohoneycomb structure, with tunnels and cavities [40].
Diatomaceous earth are fossilized 3D nanopatterned cell walls of diatoms (microalgae), called frustules [41]. The frustules are formed by amorphous biosilica, SiO2xnH2O, which is precipitated from a “soluble silicon pool”, a stabilized H4SiO4 solution [42] by several biomolecules associated with diatom cell walls, long chain polyamines (LCPAs), or proteins, such as cingulins and silaffins [43]. Such process of silicic acid polycondensation into amorphous biosilica seems to determine its high reversibility, i.e., fast release of soluble silicon species from diatom frustules [44].
The size of three-dimensional (3D) nanopatterned frustules is highly variable, from 500 nm to 50 µm [45]. The shapes are variable-drum like, triangular box, ellipsoidal circular box. The symmetry of frustule can be either pennate or centric [41]. Diatomaceous earth formed from fresh water contain lower amounts of crystalline silica compared to marine diatoms [46].
The common features determined by the common 3D nanostructure are: reversible dehydration, large volumes of free space, and high sorption capacity for various molecules and ions [40,46,47]. These features are essential for SNNMs effects for plant health promotion—Figure 1.
Reversible dehydration, sorption capacity and large volumes of pores are essential for desiccant effects involved in plant protection against pathogens and pests, and exerted on stored grains [46] and/or on leaves [32]. Reversible dehydration and sorption capacity were involved in the activation of photosynthesis after foliar application of zeolites [48].
The (nano)structure, which includes large hydrophilic surfaces able to bind water/aqueous solutions and ions (sorption capacity, reversible rehydration) including for ions and a high proportion of (nano)pores, are responsible for the soil/growing media improvers effects [22,37]. The water holding capacity, pH, and cation exchange capacity (CEC) are improved following the addition of natural zeolites [22] or kieselguhr into soil or growing media [38]. Siliceous natural nanomaterials improve the nitrogen use efficiency, mainly due to their ability to fix and then slowly release nitrogen species, including ammonium from organic fertilizers [39]. Their ability to accommodate various cations into their nanostructures positively impacts the plant utilization of macro-nutrients, e.g., potassium [40], oligo-nutrients, e.g., zinc [41], and micro-nutrients, e.g., manganese [42]. Silicate interaction with phosphates improves corn yield and reduces phosphate leaching after natural zeolites application [43].
SNNMs features related to the siliceous porous nanostructure will be further discussed in relation to the main application as inputs in the cultivated plant technologies.

3. Siliceous Natural Nanomaterials as Plant Protectants

SNNMs are known for decades as protectant of stored grain products. As we already mentioned, products based on diatomaceous earth/kieselguhr are registered for stored grain protection as plant protection products in European Union [18] and USA [33]. Table 1 exemplifies several commercial products based on diatomaceous earth, which proved to be efficient for stored commodities (grains, flour) protection.
It was demonstrated that plant protection products for stored (dried) commodities, based on diatomaceous earth, despite their efficacy and safety, have several drawbacks which limit their large scale utilization. High dose determines reduction of the bulk density of the treated stored commodities [59]. Diatomaceous earth (Protect-It® and two products originating from Serbia) has a significant negative impact on the rheological properties of dough produced from flour resulted from treated triticale and rye grains [60]. The same treatment does not influence the rheological properties of flour resulted from treated wheat grains. As could be also noted from data presented in Table 1, the effects of diatomaceous earth as stored grains protectant are related to different insect species, commodities/grain type and the commodities/grain storage conditions, moisture, and temperature [59]. High humidity reduces efficacy, due to the fact that it influences the desiccant effect. High temperature increases insect metabolism and, in general, increases also the efficacy of the desiccant products. Among the tested insect species, Tribolium confusum was demonstrated to be the most tolerant [59].
To compensate the drawbacks, several approaches were considered. One approach was to develop alternative desiccant products based on zeolites. Initially the studies demonstrated that natural zeolites need higher application dose in order to match the efficacy of products based on diatomaceous earth [61]. S. oryzae and T. castaneum proved to be more tolerant to the tested natural zeolites compared to diatomaceous earth commercial formulation Protect-It® [60]. However, other studies proved that zeolites of different origins have a better efficacy [26]. Commercial zeolites used as feed additive, originating from Greece and Slovakia, and as soil improvers, originating from Bulgaria, were tested for protection of wheat grains against S. oryzae, T. confusum, and Oryzaephilus surinamensis [26]. O. surinamensis was the most susceptible to tested zeolites and T. confusum the most tolerant. The same commercial zeolites proved to be effective against mold mite, Tyrophagus putrescentiae and the flour mite, Acarus siro, at all life stages [62]. Natural zeolites with 92% clinoptilite control bean weevils, Acanthoscelides obtectus [63]. The efficacy of stored beans protection depends on temperature and humidity. Natural zeolites registered as feed additives, originating from Slovakia and Serbia were proved to control saw-toothed grain beetle, O. surinamensis, and the rice weevil, S. oryzae, on wheat [64]. Natural zeolites, from Slovenia and Serbia, applied at 0.45 and 0.90 mg/kg, were demonstrated to be more effective than artificial zeolites against the maize weevil, Sitophilus zeamais [65]. The difference in efficacy was considered to be related to the difference in silica content.
The common features which determine good efficacy as feed additive or soil improvers, i.e., large active siliceous surface able to bind molecules, including water, and ions, are involved also in commodities protection against deleterious arthropods.
Another approach to reduce the drawbacks of the DE-based products was the combination with other natural products. Table 2 illustrates such combinations that were proven more effective than the SNNMs alone in controlling stored commodities pests.
There are also other protective effects of SNNMs on stored commodities [10]. The desiccant effect contributes also to the limitation of the development of mycotoxigenic Aspergillus flavus on stored groundnut, Arachis hypogaea [73]. SNNMs are among the efficient and affordable mycotoxin binders [9,74]. The function of SNNMs as feed additive is related also to their ability to bind mycotoxins [8,75].
SNNMs were used to control also foliar pathogens and pests. Diatomaceous earth synergize the in vitro effects of Thymus capitatus essential oils against Myzus persicae [76]. A diatomaceous earth preparation, Fossil Shield [77], registered for controlling poultry red mite, Dermanyssus gallinae, was used to control cowpea aphid, Aphis craccivora on yardlong beans, Vigna unguiculata ssp. Sesquipedalis [31]. Fossil Shield, which contains 73% amorphous SiO2, with particle dimensions varying from 5 to 30 μm, was proved to increase the efficacy of neem (Azadirachta indica) extract against cowpea aphids. The toxicity of the combination diatomaceous earth–neem extract on the coccinelidae beetle cowpea aphid predator, Menochilus sexmaculatus, was nevertheless lower than that of the recommended chemical insecticide triazophos. The same Fossil Shield was used to control Myzus persicae on globe artichoke Cynara cardunculus var. scolymus with good results [30]. Fossil Shield was applied also electrostatically, to control the mustard beetle, Phaedon cochleariae, on Chinese cabbage pak-choi, Brassica chinensis [78]. The efficacy in controlling mustard beetle was high, but the photosynthesis was reduced after dusting with diatomaceous earth. PyriSec®, the combination of diatomaceous earth, pyrethrum extract and piperonyl butoxide, used together with neem extract and biocontrol fungi Paecilomyces lilacinus, was provedto control cotton aphid, Aphis gossypii [79].
Diatomaceous earth formulation with average particle size of 2.6 µm was demonstrated to control the complex of wheat aphids, Rhopalosiphum maidis, R. padi, Sitobion avenae, S. miscanthi, Schizaphis graminum, in laboratory conditions. However, when the formulation was applied under field conditions, the efficacy was poor, even at a dose of 150 kg/ha. The high quantity of dust influences also the treated plant, reducing chlorophyll content [80].
The EU FP7 project “Developing a pool of novel and eco-efficient applications of zeolite for the agriculture sector -ECO-ZEO” (https://cordis.europa.eu/project/id/282865/reporting) intended to develop products based on zeolites to control the following foliar pests and pathogens: Ceratitis capitata (orange), Cydia pomonella and Venturia inaequalis (apple), Lobesia botrana and Plasmopara viticola (grape), and Tuta absoluta and L. botrana (tomatoes). Foliar applied zeolites were proved to be effective against V. inaequalis and P. viticola. However, for the rest of the targeted pest it needs additional active ingredients, such as azadirachtin or Bacillus thuringiensis. Until now, only the results obtained for controlling T. absoluta were published in peer-review journal [32].
The mechanism of action of SNNMs against foliar pathogens and pests is considered similar to that involved in stored grains protection–the desiccant effect. An effective desiccant effect requires formation of a particle film, covering the surface of aerial cultivated plant organs [81]. However, it was demonstrated that such desiccant effects could affect also the beneficial organisms, i.e., predatory insects [31]. Desiccant effects could negatively influence also plant pathogen antagonists or even the protected plant, by cuticle weakening. Until now, to the best of our knowledge, such effects were not investigated.
In conclusion, SNNMs effects as plant protectant is typical for basic substances, which are predominantly used as active ingredients for plant protection products. SNNMs need complementary products in order to have an acceptable level of pest/pathogen control. Under stored commodities conditions, wherein humidity could be controlled, SNNMs applied alone demonstrated an acceptable level of efficiency. However, even under such conditions, the existing drawbacks determine formulations with other active substances. Under field conditions SNNMs act mainly as adjuvant to other active ingredients with action against pests and/or pathogens.

4. Siliceous Natural Nanomaterials as Plant Strengtheners

Plant strengtheners are considered at present equivalent with plant biostimulants [15,37]. Europe is the leader of the plant biostimulants, with almost 40% of the world sale [35]. Several EU countries developed a legislative framework, separate from the EU legislation, which promotes low-risk agricultural inputs [37]. In Germany, such products were called plant strengtheners (Pflanzenstärkungsmittel), in Italy invigorants (Corroboranti), in Spain, means of phytosanitary defense (Medios de defensa fitosanitaria, MDF), in France, natural substances for use as biostimulants (Substances naturelles à usage biostimulant) [36]. The complete list of these different names is presented by Caradonia et al. [35]. However, there are some differences related to the definition of these agro-inputs. Plant strengtheners were defined in Germany as “substances and mixtures, including microorganisms, that are intended solely to serve the general health maintenance of plants” or “are intended to protect plants from non-parasitic damage”, without being a plant protection product [82]. The EU Regulation 1009/2019, Art. 47, paragraph (2) defines plant biostimulants as “a product stimulating plant nutrition processes independently of the product nutrient content with the sole aim of improving one or more of the following characteristics of the plant or the plant rhizosphere: (a) nutrient use efficiency; (b) tolerance to abiotic stress; (c) quality traits; (d) availability of confined nutrients in soil or rhizosphere.” Therefore, the definition of plant biostimulants by EU Regulation involves also the influence on nutrient and nutrient uptake, not “only general health maintenance of plants”, and enhanced tolerance to abiotic stress/protection from non-parasitic damage.
In the USA, the emerging legislative framework seems to consider soil improvers as a category of plant biostimulants. Last year, US Environmental Protection Agency (EPA) released a draft guidance regarding plant biostimulants which describes this category of agricultural inputs as “a naturally-occurring substance […] that […] improves the physical, chemical, and/or biological characteristics of the soil as a medium for plant growth.”
This discussion regarding legal framework is intended mainly to underline the need to consider both indirect/mediated and direct effects of the SNNMs on plants as being related to plant strengtheners/plant biostimulants effects. Such approach is not limited only to these siliceous natural minerals. Microbial plant biostimulants have both direct and indirect/mediated effects on plants. The bacteria from Azospirillum genera, largely recognized as plant biostimulants, produce siderophores, which modify the iron bioavailability into rhizosphere; therefore, fulfill the criteria of Art. 47 paragraph (2), because they enhance the “availability of confined nutrients in soil or rhizosphere”. Mycorrhizae fungi, other characteristic microbial plant biostimulants, influence not only directly the plant biology, but also indirectly, due to the production of glomalin. Glomalin improves soil structure and soil resistance to erosion and reduces the effects of heavy metals.
The organic, non-microbial plant biostimulants have also indirect effects. Humic and fulvic acids have typical indirect effects, improving soil characteristics and nutrient availability in the rhizosphere. Similar indirect effects are demonstrated also for other organic plant biostimulants applied to soil, such as protein hydrolysate. Both mentioned organic plant biostimulants classes exert also direct effects on plant physiology.
The indirect/(soil) mediated effects of plant biostimulants overlap with effects of soil conditioners/soil improvers. The main difference is related to the dose. Plant biostimulants are applied in smaller quantities compared to soil improvers. The main class of organic plant biostimulants is produced from materials initially used as soil amendments (Figure 2).
Overall, the improvement effects on soils/growing substrate promote not only better plant nutrition, but also plant health and/or plant resistance to abiotic stress [83,84]. Increased yield, including under stress conditions, were found for plant cultivated on growing media/soil treated with SNNMs [84,85]. In the following subsections we will present and discuss the evidences of SNNMs indirect and direct effects related to plant protection against abiotic stress, improvement of nutrient uptake and use efficiency, crop quality—i.e., plant strengthening effects.

4.1. Mediated Plant Strengthening Effects

SNNMs, and especially zeolites, were largely used for the improvement of poor soil, especially sandy and clay soil [86], and/or for the improvement of soil affected by salinity or heavy metal contaminations. Their effects on the crop are exemplified in Table 3.
Data from Table 3 demonstrate: improved nutrient uptake, increased nutrient use efficiency, protection against abiotic stress (salinity, drought, heavy metals contamination) and enhanced crop quality. Such effects, similar with those described for plant biostimulants, are amplified by application of foliar treatment with known plant biostimulants. For example, zeolites were applied in combination with foliar treatment with melatonin [93], proline [94], selenium [91], or seed inoculation with metal-tolerant microorganisms [92]. In some cases, zeolites were more effective when applied together with amendments such as biochar [94].
Zeolites were much more studied compared to diatomaceous earth as soil amendments and Si sources for alleviation of abiotic stress-induced effects in plants, especially regarding salinity and heavy metal-induced stress. Only very recently, deionized diatomite was found to efficiently absorb Na+ and Cl- ions from aqueous solutions, presenting promising results in alleviating stress-induced negative effects on plants [96]. Although there are several studies investigating decontamination and removal of heavy metals from soils and wastewater by diatomaceous earth ([97,98,99,100]), we have found no study involving the capacity to reduce heavy metal-induced stress on plants.
Plant biostimulants were defined as a separate category of agricultural products, which promote cultivated plant growth and cultivated plant health without being nutrients, soil improvers, or plant protection products [101]. However, as we already mentioned, the intended use (e.g., protection of the cultivated plants against abiotic stress) is similar for both plant biostimulants and SNNMs used as soil improvers in soil affected by heavy metal contamination or sodicity, and/or from semi-arid area, with high drought risk. One of the main classes of plant biostimulants, humic acids, is described also as soil improver. Humic acid derived from lignite were used to improve the properties of poor soil–medium and coarse textured soil properties, in a pot experiment [102]. The quantity used for the pot experiment, 12.4 g per 5 kg of growth substrate is of the same order of magnitude with that of zeolites used to remediate the lead pollution in a pot experiment, wherein a maximum of 20 g per kg of growth substrate was used [103]. Humic acid amendment was proven to enhance corn tolerance to drought and phosphorus deficiency stress [104]. Humic acid amendment applied to soil, combined with foliar applied Zn and Se reduces Cd accumulation in tobacco [105]. The similarities with the effects described for SNNMs applied as soil improvers/soil amendment are significant. Therefore, in our opinion, there are enough arguments to consider the SNNMs application to soil/growing substrates, not only as soil improvers but also as a cultivated plant strengthening method.

4.2. Direct Plant Strengthening Effects

One potential direct effect of foliar applied SNNMs on treated plants is related to the activation of photosynthesis [81]. This effect was related to the capacity of SNNMs to concentrate CO2 on treated leaves, near stomata [81]. SNNMs are well-known for their capacity to act as reversible CO2 (chemo)sorbent [106,107]. Selective enrichment of the proximate stomata microenvironment should enhance CO2 fixation, especially in C3 plants. This potential effect of zeolites on photosynthesis was demonstrated until now in only one publication [48]. A related siliceous nanomaterial, kaolin, was applied as reflective anti-transpirant [108] and photosynthesis and gas-exchange enhancer [109]. A particle film is formed by foliar spraying. The coverage of the canopy reduces leaf temperature, reflects the damaging UV-b radiation, enhances gas-exchange and improves photosynthesis in sweet orange [110], red grapefruit [111], olive [109] and grape [112]. Photosynthesis inhibition was noted after kaolin dusting on apple, hazelnut, and walnut. Similar effect was observed after diatomaceous earth application on Chinese cabbage [113].
The difference observed (photosynthesis enhancement versus inhibition) was explained to be a result of the water status in plant, based on recent experiments done on grape. On well-watered grape plants, kaolin reduces the photosynthetic performance [114]. On water stressed grape plants, kaolin functions as leaf protection agent [115]. Kaolin function as anti-transpirant and leaf protectant was recently reviewed [108]. Kaolin was considered an emerging tool to mitigate the effects of adverse abiotic stress on cultivated plants [116]. Despite the fact that foliar application of kaolin determines effects very similar to those of plant biostimulants (higher plant tolerance to abiotic stress, enhanced crop quality), kaolin has not been considered yet as plant biostimulant.
This direction of photosynthesis stimulation by SNNMs under light and water stress is interesting and merits further investigation, also in relationship with the plant biostimulants mechanism of action. In general, plant biostimulants/plant strengtheners amplify the photosynthesis of treated plants under stress conditions [117]. Such effect was proven for microbial plant biostimulants [118,119], organic plant biostimulants [120], and inorganic plant biostimulants [121,122]. However, there is another aspect related to photosynthesis, which was not investigated enough in relation to plant strengthening/plant biostimulant effects. Boosting reactive oxygen species (ROS) production was constantly demonstrated after the application of various types of plant biostimulants [123,124,125,126]. ROS are involved in the response of plants to stress. The plants treated with plant biostimulants demonstrated an increased tolerance to imbalance determined by the increased ROS production [117,124,127,128,129]. Despite the fact that chloroplasts are well known as a source of ROS production [130], the research related to plant biostimulants mechanism of action has not considered chloroplasts involvement yet. It was demonstrated that chloroplasts are mediators of plant response to abiotic stress. For example, plant biostimulant Trichoderma strain increased the chloroplasts number and size in Passiflora caerulea leaves [119]. One explanation for this chloroplasts proliferation after plant biostimulant treatment could be in relationship with such mechanism of action, related to balanced ROS production by chloroplasts.
Other direct plant strengthening effects are in relation to soluble silicon species release from SNNMs. These will be further discussed, after a presentation of the present knowledge of the role of silicon in plant physiology.

Release of Soluble Silicon Species

In the last decades, an overwhelming body of evidences proved that Si is a limiting factor for crop production, particularly in soils that have a low soluble Si pool and for known Si-accumulating plants such as grass/cereals [131]. There are evidences suggesting that Si is essential, also, for non-grass species angiosperms [132]. Recently, it was hypothesized that silicon is essential for an efficient legume–rhizobia interaction and symbiotic nitrogen fixation [133,134]. Despite all of these evidences of silicon as limiting factor in cultivated plant productivity, silicon is still not considered an essential element/nutrient in plant, because it does not fulfill the plant nutrient criteria [135,136]. Rather, the soluble silicon effects on plants are characteristic for plant strengtheners/plant biostimulants [137]. Soluble silicon species promote plant health, improve plant resistance to biotic and abiotic stress [138,139,140], increase nutrient uptake and nutrient use efficiency [141], reduce heavy metals toxicity [142,143]. However, in order to accommodate the evidences related to the contribution of soluble silicon to plant yield, with the classical Liebig barrel and the nutrients included in it, silicon is for now considered only “beneficial rather than essential plant nutrient” [144].
Silicon has both morpho-structural and physiological/biochemical functions in plants [145]. Deposition of soluble silicon as silica layer beneath the cuticle generates a physical barrier for plant pathogens [146], phloem feeding insects [147], leaf eating larvae [148], and herbivores like locusts and small rodents [149]. The biochemical mechanisms of silicon action are not known yet, but there are evidences which suggest a regulatory function in plants. Soluble Si alleviate water stress (Sacala, 2009), nutrient imbalance (Ma and Yamaji, 2008) and lodging (Kashiwagi et al., 2008), due to activation of plant defense against abiotic stress. Silicon protects plants against saline stress by reducing the oxidative stress [150], chloride [151], and sodium uptake [152], and by enhancing potassium transport [153]. Similar effects, of reduced oxidative stress and reduced uptake of non-nutrient metal ions from soil solution, were demonstrated in relation with protective effects of soluble Si against heavy metals [142]. For the reduced uptake of heavy metals from soil are responsible also mechanisms of co-deposition of metals and Si, both externally, in the rhizosphere, and internal, inside plant roots [154]. A meta-analysis on soluble silicon alleviation of abiotic stress on several Angiosperm families revealed a similar mechanism, which involves significant reduction in markers of oxidative stress, such as peroxylipid (determined with reactive based on malondialdehyde, MDA) and H2O2 [139].
The importance of soluble Si in plant physiology results, also, from its role on simultaneous and non-antagonistic activation of the different pathways related to defense system [155]. Plant systemic defense against biotic and abiotic stress is regulated by several pathways: of salicylic acid (SA), of jasmonic acid (JA) and of abscisic acid (ABA) [156,157,158]. In general, SA is associated with resistance to biotrophic pathogens and sucking/phloem feeding insects, and JA is associated with resistance to the necrotrophic pathogens and cutting and chewing insects/herbivores and ABA is related to abiotic stress. The SA and JA pathways are antagonistic, generating a balancing between resistance to biotrophic pathogens/phloem feeding insects and necrotrophic pathogens/cutting and chewing herbivores. Various types of abiotic stress (extreme temperatures, solar radiation, and chemical pro-oxidant agents) interfere with SA/JA/ABA pathways, including through modulation of the level of reactive oxygen [159] and nitrogen species/nitric oxide [160]. All of these interactions could determine an increased plant susceptibility to biotic stress factors controlled by other pathway than the activated one [156,157]. Soluble Si balances these cross-talking pathways related to plant defense and prime broad-spectrum resistance to biotic stress [155]. A flow of soluble silicon through cytoplasm and further deposition on cell wall/plant extracellular matrix seem to be essential for silicon priming in plants [161]. Deposition of silicon into plant cell wall is mainly done as amorphous silica, which interferes with further biorefinery processes [162].
The soluble Si species up-taken by plants from the soil solution is mono-silicic acid, H4SiO4 [163], through an active transport system [146]. The mono-silicic acid concentration in soil ranges from 0.1 mM to 0.6 mM [163], which is less than 10–60 folds its saturation point [164]. The soluble Si pool in soil results mainly from the recycled Si accumulated in plants (phytogenic Si), SiO2xnH2O, an amorphous, hydrated, and highly porous material, produced by silicic acid molecules mutual polycondensation [131]. Chemical weathering of silicate minerals from parental rock does not replenish soluble soil Si pool, despite the fact that silicon is the second mineral in earth crust [165], but rather determines soil desilication [144]. The moderate mobile H4SiO4 is immobilized due to the reaction with immobile Al and Fe ions resulted from weathered parental rock and formation of secondary clays [166]. Therefore, the main source of soluble silicon in the soil is considered the bio/phyto silica–amorphous silica/opal SiO2xnH2O, deposited in plant cell wall.
Release of soluble Si from phytogenic Si is done by microorganisms responsible for plant residues decomposition [167]. Despite the fact that Si solubilizing microorganisms from phytogenic Si could be very useful plant biostimulants (accelerating soluble Si pool replenishing) there are practically no studies into this direction. It was reported that arbuscular mycorrhizal fungi (AMF) collected from saline sites accumulate Si and transfer it to host plants [168], but this is in relation with an enhanced uptake of soluble Si (like other nutrients) by AMF, and it is not related to an accelerated soluble Si release into soil.
There are practically no studies related to phytogenic Si solubilization by microorganisms. In aquatic systems biogenic Si dissolution is promoted by microbial consortia [169], by degradation of the organic matter wherein biogenic Si is embedded. A similar mechanism is most likely to be responsible for phytogenic Si solubilization in soil environment. However, besides the enzymes responsible for lignocellulose degradation, microbial metabolites, which enhance silicon/H4SiO4 dissolution from amorphous phytogenic Si, should be also involved. Such microbial metabolites have not been identified yet, but it is known that H4SiO4 equilibrium in solution is influenced by alkaline cations, organic acids, and polyamines [164]. Among the environmental friendly additives used to prevent silica fouling in water pipes, catechuic acid (3, 4-dihydroxybenzoic acid), gallic acid (3, 4, 5-trihydroxybenzoic acid), dopamine, citric acids, and amino acids were the most effective [170]. Putrescine and their homologues [171], spermidine and spermine [172], and other long chain biogenic polyamines [164] influence silicon species equilibrium in unsaturated solutions. Such substances could be produced by several plant beneficial microorganisms.
Among these metabolites, several are directly related to the effects of plant biostimulants. Catechuic acid derivatives are well known as one of the main category of siderophores responsible for plant growth promotion effects of rhizobacteria [173,174]. Gallic acid accumulates in wheat treated with salt tolerant rhizobacteria [175]. Rhizobacteria producing polyamines (Pas) stimulate plant growth–Azospirillum producing cadaverine [176], Streptomyces producing putrescine [177], Bacillus producing spermidine [178]. Therefore, Si solubilizing microorganisms could represent an effective category of microbial plant biostimulants. However, until now there is no systematic investigation focused on the effects of SNNMs applications as soil conditioners on Si solubilizing microorganisms.
Soluble silicon species are formed mainly from diatomaceous earth. Its structure is formed mainly by amorphous silica, SiO2xnH2O and is similar to that of phytogenic silica. Zeolites release soluble silicon species mainly by weathering. The flow of silicon through plant tissues supports the formation of amorphous silica–plant opal, SiO2xnH2O. Silicon deposition, generating apoplastic obstruction [136] was hypothesized to be the main mechanism of action which protects plants against biotic and abiotic stress—Figure 3.
Other hypothesized mechanisms recently reviewed [122,135] refer also to the transport of soluble silicon species through plant tissues and polycondensation after concentration into the aerial parts due to transpiration.
SNNMs supply plants with soluble silicon. Application of 600 kg/ha of diatomaceous earth, in combination with standard fertilization practice promotes rice growth and increases yield [19]. A commercial preparation of diatomaceous earth, Agrisilica® (AgriPower, Sydney, Australia), which is formed from Melosira granulate frustules, with 26% silica, was demonstrated to increase the yield of melon when applied in dose of 600 and 800 kg/ha to the coarse soil from Northeastern Brazil [95]. The same commercial product determined an increase of sugar beet yield, up to 40%, in Morocco [179], and proved to be an efficient source for sugarcane in sandy soil in Brazil [180]. Applied at 150 kg/ha, diatomaceous earth increased the potato tuber yield by 38.7% [181]. A commercial preparation of diatomaceous earth (Perma-Guard, Inc., Kamas, UT, USA) was used to compensate the water stress in potted ornamentals, black-eyed Susan, Rudbeckia hirta, dahlia, Dahlia Cav. × hybrida and daisy, Gerbera jamesonii. Si-rich mineral zeolite protects barley plants grown in hydroponics against cadmium stress [21].
Application of SNNMs as source of soluble silicon species could compensate the decrease of phytogenic Si inputs into soil, impacted by anthropogenic biomass removal [182,183]. Additional studies are necessary for a better exploitation of this potential SNNMs application.

5. Conclusions and Further Perspectives

Evidences regarding siliceous natural nanomaterials as biorationals for integrated farming systems were presented. However, there are gaps in knowledge that limit their large scale utilization. Figure 4 illustrates such gaps related to SNNMs effects on (micro)organisms associated to microbiocenosis delimitated by plant organs, in relation to their main effects.
Similar to other biorationals from the category of basic substances with low risk, SNNMs efficacy as plant protectants and plant health strengtheners is rather low. Complementary active ingredients should be used to enhance the effects of SNNMs on treated plants. For SNNMs applied as protectants of stored seeds such strategy, of using complementary biorationals/low risk substances, proved to be highly effective.
Natural zeolites are excellent soil improvers, especially in poor soil. However, their effects are not limited to the improvement of chemical and physical characteristics. Natural zeolites seem to influence also the recruitment and promotion of beneficial rhizosphere microorganisms, but there is a limited number of studies and information. Recently, it was reported that the application of natural green tuff stimulates the development of several phylotypes belonging to Bacillales [184]. Further studies are necessary to understand the mechanisms behind such effects on beneficial microorganisms. Three-dimensional (3D) SNNMs porous structures, especially of diatomaceous earth, could provide shelter for bacteria against grazing protozoa. Reversible sorption and ion exchange capacity could modulate bioavailability of bioactive molecules, such as antibiotics, quorum sensing signals or siderophores, and respectively, of essential or potential toxic elements.
SNNMs foliar application is still on its infancy. The combination with foliar fertilizer should benefit from the excellent ion-exchange capabilities of zeolites. To the best of our knowledge, SNNMs were not used as carrier for foliar fertilizer until now. As foliar application, diatomaceous earth could be exploited better as anti-transpirant and leaf protector by cleaning the fossilized frustules to their initial state of transparency. The frustules of diatoms are transparent “house” for photosynthetic organisms, protecting them against damaging UV radiation [185] and stimulating photosynthesis [186]. The abrasiveness of SNNMs applied on leaves could be used to promote the release of volatile signals and predators recruitment.
Particle film formation is an agricultural technology which was demonstrated to protect plants against both biotic [187,188] and abiotic stress [108]. Recently, it was demonstrated that micronized chabazitic zeolites, applied together with microorganisms, present superior particle forming ability and enhanced efficacy in controlling tomato diseases [189]. Diatomaceous earth synergizes the effects of Metarhizium flavoviride against western flower thrips, Frankliniella occidentalis, an invasive pest [190]. Therefore, the potential for synergy between SNNMs and phyllosphere plant beneficial microorganisms, in connection to particle film formation technology, seems to be significant and requires more attention.
Diatomaceous earth are not only grain protectant, but are also bioactive carriers for seed coating. Applied together with vermicompost and soy flours, diatomaceous earth promotes seedling growth of a cover crop mixture grass-legumes, perennial ryegrass, Lolium perenne, and red clover, Trifolium pretense [191]. Further studies regarding the effects on seed viability, seed priming, and on microbial plant biostimulants applicable as seed inoculant could generate new solutions for sustainable farming.
The combination of SNNMs with microbial plant biostimulants has significant potential to be synergic for plant health strengthening effects. The microbial plant biostimulants should promote the release of soluble silicon species. Soluble silicon should enhance the microbial plant biostimulants effects related to nutrient use efficiency, enhanced plant tolerance to stress and crop quality.
Natural zeolites and diatomaceous earth have complementary features—e.g., high ion-exchange capacity and, respectively, the ability to release soluble silicon. Their optimal combination could lead to additive/synergic effects, which should promote their use as biorationals.

Author Contributions

Conceptualization, F.O.; writing—review and editing, D.C.-A., C.L., and F.O.; project administration, F.O. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by Romanian Ministry of Agriculture and Rural Development, project “Research on the biological activity of some nanomaterial-based products on major pest and pathogens of fruit trees and assessment of the ecotoxicological impact of these on useful entomofauna–ADER 7.3.9.” The APC was funded by project ADER 7.3.9.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Mumpton, F.A. La roca magica: Uses of natural zeolites in agriculture and industry. Proc. Natl. Acad. Sci. USA 1999, 96, 3463–3470. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  2. Ghobara, M.M.; Mohamed, A. Diatomite in Use: Nature, Modifications, Commercial Applications and Prospective Trends; Scrivener Publishing Llc: Beverly, CA, USA, 2019; pp. 471–509. [Google Scholar]
  3. Ivkovic, S.; Deutsch, U.; Silberbach, A.; Walraph, E.; Mannel, M. Dietary supplementation with the tribomechanically activated zeolite clinoptilolite in immunodeficiency: Effects on the immune system. Adv. Ther. 2004, 21, 135–147. [Google Scholar] [CrossRef] [PubMed]
  4. Kraljević Pavelić, S.; Simović Medica, J.; Gumbarević, D.; Filošević, A.; Pržulj, N.; Pavelić, K. Critical Review on Zeolite Clinoptilolite Safety and Medical Applications in vivo. Front. Pharmacol. 2018, 9. [Google Scholar] [CrossRef] [PubMed]
  5. Sadowska, A.; Świderski, F. Sources, Bioavailability, and Safety of Silicon Derived from Foods and Other Sources Added for Nutritional Purposes in Food Supplements and Functional Foods. Appl. Sci. 2020, 10, 6255. [Google Scholar] [CrossRef]
  6. Additives, E.P.O. Scientific Opinion on the safety and efficacy of clinoptilolite of sedimentary origin for all animal species. Efsa J. 2013, 11, 3039. [Google Scholar]
  7. Olteanu, M.; Saracila, M.; Ropota, M.; Turcu, R.P.; Dragotoiu, D.; Marin, M.P.; Pogurschi, E.N. Volcanic tuff, potential source of minerals in dairy cows feeding. Agro Life Sci. J 2019, 8, 206–213. [Google Scholar]
  8. Boudergue, C.; Burel, C.; Dragacci, S.; Favrot, M.C.; Fremy, J.M.; Massimi, C.; Prigent, P.; Debongnie, P.; Pussemier, L.; Boudra, H. Review of mycotoxin-detoxifying agents used as feed additives: Mode of action, efficacy and feed/food safety. Efsa Support. Publ. 2009, 6, 22E. [Google Scholar] [CrossRef]
  9. Vila-Donat, P.; Marín, S.; Sanchis, V.; Ramos, A. A review of the mycotoxin adsorbing agents, with an emphasis on their multi-binding capacity, for animal feed decontamination. Food Chem. Toxicol. 2018, 114, 246–259. [Google Scholar] [CrossRef] [Green Version]
  10. Lupu, C.; Delian, E.; CHIRA, L.; Chira, A. New insights into the multiple protective functions of diatomaceous earth during storage of agricultural products. Sci. Pap. Ser. A-Agron. 2018, 61, 487–496. [Google Scholar]
  11. Dos Anjos, F.R.; Ledoux, D.R.; Rottinghaus, G.E.; Chimonyo, M. Efficacy of Mozambican bentonite and diatomaceous earth in reducing the toxic effects of aflatoxins in chicks. World Mycotoxin J. 2016, 9, 63–72. [Google Scholar] [CrossRef]
  12. Martinovic, S.; Vlahovic, M.; Boljanac, T.; Pavlovic, L. Preparation of filter aids based on diatomites. Int. J. Miner. Process. 2006, 80, 255–260. [Google Scholar] [CrossRef]
  13. Braun, F.; Hildebrand, N.; Wilkinson, S.; Back, W.; Krottenthaler, M.; Becker, T. Large-scale study on beer filtration with combined filter aid additions to cellulose fibres. J. Inst. Brew. 2011, 117, 314–328. [Google Scholar] [CrossRef]
  14. Gómez, J.; Gil, M.L.A.; de la Rosa-Fox, N.; Alguacil, M. Diatomite releases silica during spirit filtration. Food Chem. 2014, 159, 381–387. [Google Scholar] [CrossRef] [PubMed]
  15. Feldmann, F.; Carstensen, C. Efficacy and risks of ”biorationals“. J. Plant Dis. Prot. 2018, 125, 517–521. [Google Scholar] [CrossRef]
  16. Matyjaszczyk, E. “Biorationals” in integrated pest management strategies. J. Plant Dis. Prot. 2018, 125, 523–527. [Google Scholar] [CrossRef] [Green Version]
  17. Commision, E. Regulation (EC) No 1107/2009. Available online: https://eur-lex.europa.eu/legal-content/EN/TXT/HTML/?uri=CELEX:32009R1107&from=EN (accessed on 10 October 2020).
  18. Anastassiadou, M.; Arena, M.; Auteri, D.; Brancato, A.; Bura, L.; Carrasco Cabrera, L.; Chaideftou, E.; Chiusolo, A.; Marques, D.C. Peer review of the pesticide risk assessment of the active substance kieselgur (diatomaceous earth). Efsa J. 2020, 18, e06054. [Google Scholar]
  19. Sandhya, K.; Prakash, N.B.; Meunier, J.D. Diatomaceous earth as source of silicon on the growth and yield of rice in contrasted soils of Southern India. J. Soil Sci. Plant Nutr. 2018, 18, 344–360. [Google Scholar] [CrossRef] [Green Version]
  20. Riotte, J.; Sandhya, K.; Prakash, N.B.; Audry, S.; Zambardi, T.; Chmeleff, J.; Buvaneshwari, S.; Meunier, J.D. Origin of silica in rice plants and contribution of diatom Earth fertilization: Insights from isotopic Si mass balance in a paddy field. Plant Soil 2018, 423, 481–501. [Google Scholar] [CrossRef]
  21. Balakhnina, T.I.; Bulak, P.; Matichenkov, V.V.; Kosobryukhov, A.A.; Wlodarczyk, T.M. The influence of Si-rich mineral zeolite on the growth processes and adaptive potential of barley plants under cadmium stress. Plant Growth Regul. 2015, 75, 557–565. [Google Scholar] [CrossRef]
  22. Ramesh, K.; Biswas, A.K.; Patra, A.K. Zeolitic farming. Indian J. Agron. 2015, 60, 185–191. [Google Scholar]
  23. Li, D.Y.; Joo, Y.K.; Christians, N.E.; Minner, D.D. Inorganic soil amendment effects on sand-based sports turf media. Crop Sci. 2000, 40, 1121–1125. [Google Scholar] [CrossRef]
  24. Pratt, C.; Kingston, K.; Laycock, B.; Levett, I.; Pratt, S. Geo-Agriculture: Reviewing Opportunities through Which the Geosphere Can Help Address Emerging Crop Production Challenges. Agronomy 2020, 10, 971. [Google Scholar] [CrossRef]
  25. Korunić, Z.; Liška, A.; Lucić, P.; Hamel, D.; Rozman, V. Evaluation of diatomaceous earth formulations enhanced with natural products against stored product insects. J. Stored Prod. Res. 2020, 86, 101565. [Google Scholar] [CrossRef]
  26. Rumbos, C.I.; Sakka, M.; Berillis, P.; Athanassiou, C.G. Insecticidal potential of zeolite formulations against three stored-grain insects, particle size effect, adherence to kernels and influence on test weight of grains. J. Stored Prod. Res. 2016, 68, 93–101. [Google Scholar] [CrossRef]
  27. Mortazavi, H.; Toprak, U.; Emekci, M.; Bagci, F.; Ferizli, A.G. Persistence of diatomaceous earth, SilicoSec® against three stored grain beetles. J. Stored Prod. Res. 2020, 89, 101724. [Google Scholar] [CrossRef]
  28. Fallik, E. Physical control of mycotoxigenic fungi. In Mycotoxins in Fruits and Vegetables; Elsevier: Amsterdam, The Netherlands, 2008; pp. 297–310. [Google Scholar]
  29. Chulze, S. Strategies to reduce mycotoxin levels in maize during storage: A review. Food Addit. Contam. 2010, 27, 651–657. [Google Scholar] [CrossRef]
  30. El-Wakeil, N.E.; Saleh, S.A. Effects of neem and diatomaceous earth against Myzus persicae and associated predators in addition to indirect effects on artichoke growth and yield parameters. Arch. Phytopathol. Plant Prot. 2009, 42, 1132–1143. [Google Scholar] [CrossRef]
  31. Ulrichs, C.; Mewis, I.; Schnitzler, W. Efficacy of neem and diatomaceous earth against cowpea aphids and their deleterious effect on predating Coccinelidae. J. Appl. Entomol. 2001, 125, 571–575. [Google Scholar] [CrossRef]
  32. De Smedt, C.; Van Damme, V.; De Clercq, P.; Spanoghe, P. Insecticide effect of zeolites on the tomato leafminer Tuta absoluta (Lepidoptera: Gelechiidae). Insects 2016, 7, 72. [Google Scholar] [CrossRef] [Green Version]
  33. Leahy, J.; Mendelsohn, M.; Kough, J.; Jones, R.; Berckes, N. Biopesticide oversight and registration at the US Environmental Protection Agency. In Biopesticides: State of the Art and Future Opportunities; ACS Publications: Washington, DC, USA, 2014; pp. 3–18. [Google Scholar]
  34. Tőkés, G.; Ripka, G. Regulation and use of biological control agents in Hungary. Eppo Bull. 2016, 46, 263–269. [Google Scholar] [CrossRef]
  35. Caradonia, F.; Battaglia, V.; Righi, L.; Pascali, G.; La Torre, A. Plant Biostimulant Regulatory Framework: Prospects in Europe and Current Situation at International Level. J. Plant Growth Regul. 2019, 38, 438–448. [Google Scholar] [CrossRef]
  36. La Torre, A.; Battaglia, V.; Caradonia, F. An overview of the current plant biostimulant legislations in different European Member States. J. Sci. Food Agric. 2016, 96, 727–734. [Google Scholar] [CrossRef] [PubMed]
  37. Torre, L.; Battaglia, V.; Caradonia, F. Legal aspects of the use of plant strengtheners (biostimulants) in Europe. Bulg. J. Agric. Sci 2013, 19, 1183–1189. [Google Scholar]
  38. Król, M. Natural vs. Synthetic Zeolites. Crystals 2020, 10, 622. [Google Scholar] [CrossRef]
  39. Nakhli, S.A.A.; Delkash, M.; Bakhshayesh, B.E.; Kazemian, H. Application of Zeolites for Sustainable Agriculture: A Review on Water and Nutrient Retention. Water Air Soil Pollut. 2017, 228, 34. [Google Scholar] [CrossRef]
  40. Eroglu, N.; Emekci, M.; Athanassiou, C.G. Applications of natural zeolites on agriculture and food production. J. Sci. Food Agric. 2017, 97, 3487–3499. [Google Scholar] [CrossRef]
  41. Panwar, V.; Dutta, T. Diatom biogenic silica as a felicitous platform for biochemical engineering: Expanding frontiers. ACS Appl. Bio Mater. 2019, 2, 2295–2316. [Google Scholar] [CrossRef]
  42. Spinde, K.; Pachis, K.; Antonakaki, I.; Paasch, S.; Brunner, E.; Demadis, K.D. Influence of polyamines and related macromolecules on silicic acid polycondensation: Relevance to “Soluble Silicon Pools”? Chem. Mater. 2011, 23, 4676–4687. [Google Scholar] [CrossRef]
  43. Lechner, C.C.; Becker, C.F.W. Silaffins in Silica Biomineralization and Biomimetic Silica Precipitation. Mar. Drugs 2015, 13, 5297–5333. [Google Scholar] [CrossRef] [Green Version]
  44. Gautier, C.; Livage, J.; Coradin, T.; Lopez, P.J. Sol–gel encapsulation extends diatom viability and reveals their silica dissolution capability. Chem. Commun. 2006, 44, 4611–4613. [Google Scholar] [CrossRef]
  45. Medarevic, D.P.; Losic, D.; Ibric, S.R. Diatoms—Nature materials with great potential for bioapplications. Hem. Ind. 2016, 70, 613–627. [Google Scholar] [CrossRef] [Green Version]
  46. Korunic, Z. Diatomaceous earths, a group of natural insecticides. J. Stored Prod. Res. 1998, 34, 87–97. [Google Scholar] [CrossRef]
  47. McCoy, E.L. Commercial Amendments for Sand-based Root Zones: Review and Interpretation. HortTechnology 2013, 23, 803–813. [Google Scholar] [CrossRef]
  48. De Smedt, C.; Steppe, K.; Spanoghe, P. Beneficial effects of zeolites on plant photosynthesis. Adv. Mater. Sci. 2017, 2, 1–11. [Google Scholar] [CrossRef] [Green Version]
  49. Liška, A.; Rozman, V.; Korunić, Z.; Halamić, J.; Galović, I.; Lucić, P.; Baličević, R. The potential of Croatian diatomaceous earths as grain protectant against three stored-product insects. Integr. Prot. Stored Prod. Iobc-Wprs Bull. 2015, 111, 107–113. [Google Scholar]
  50. Vayias, B.; Athanassiou, C. Factors affecting the insecticidal efficacy of the diatomaceous earth formulation SilicoSec against adults and larvae of the confused flour beetle, Tribolium confusum DuVal (Coleoptera: Tenebrionidae). Crop Prot. 2004, 23, 565–573. [Google Scholar] [CrossRef]
  51. Athanassiou, C.G.; Kavallieratos, N.G.; Tsaganou, F.C.; Vayias, B.J.; Dimizas, C.B.; Buchelos, C.T. Effect of grain type on the insecticidal efficacy of SilicoSec against Sitophilus oryzae (L.) (Coleoptera: Curculionidae). Crop Prot. 2003, 22, 1141–1147. [Google Scholar] [CrossRef]
  52. Athanassiou, C.G.; Kavallieratos, N.G.; Tsakiri, J.B.; Xyrafidis, S.N.; Vayias, B.J. Effect of Temperature and Humidity on Insecticidal Effect of SilicoSec Against Ephestia kuehniella (Lepidoptera: Pyralidae) Larvae. J. Econ. Entomol. 2006, 99, 1520–1524. [Google Scholar] [CrossRef]
  53. Korunic, Z.; Fields, P. Diatomaceous Earth Insecticidal Composition. U.S. Patent 5773017, 6 June 1998. [Google Scholar]
  54. Arnaud, L.; Tran Thi Lan, H.; Brostaux, Y.; Haubruge, E. Efficacy of diatomaceous earth formulations admixed with grain against populations of Tribolium castaneum. J. Stored Prod. Res. 2005, 41, 121–130. [Google Scholar] [CrossRef] [Green Version]
  55. Athanassiou, C.G.; Kavallieratos, N.G. Insecticidal effect and adherence of PyriSec® in different grain commodities. Crop Prot. 2005, 24, 703–710. [Google Scholar] [CrossRef]
  56. Athanassiou, C.G.; Kavallieratos, N.G.; Chiriloaie, A.; Vassilakos, T.N.; Fatu, V.; Drosu, S.; Ciobanu, M.; Dudoiu, R. Insecticidal efficacy of natural diatomaceous earth deposits from Greece and Romania against four stored grain beetles: The effect of temperature and relative humidity. Bull. Insectol. 2016, 69, 25–34. [Google Scholar]
  57. Aldryhim, Y.N. Efficacy of the amorphous silica dust, Dryacide, against Tribolium confusum Duv. and Sitophilus granarius (L.) (Coleoptera: Tenebrionidae and Curculionidae). J. Stored Prod. Res. 1990, 26, 207–210. [Google Scholar] [CrossRef]
  58. Athanassiou, C.G.; Kavallieratos, N.G.; Economou, L.P.; Dimizas, C.B.; Vayias, B.J.; Tomanović, S.; Milutinović, M. Persistence and Efficacy of Three Diatomaceous Earth Formulations Against Sitophilus oryzae (Coleoptera: Curculionidae) on Wheat and Barley. J. Econ. Entomol. 2005, 98, 1404–1412. [Google Scholar] [CrossRef] [PubMed]
  59. Korunić, Z. Overview of undesirable effects of using diatomaceous earths for direct mixing with grains. Pestic. I Fitomedicina 2016, 31, 9–18. [Google Scholar] [CrossRef]
  60. Perisic, V.; Perisic, V.; Hadnadev, M.; Dekic, V.; Dapcevic-Hadnadev, T.; Vukovic, S.; Vukajlovic, F. Impact of diatomaceous earth application on the rheological properties of wheat, triticale and rye flour dough. J. Stored Prod. Res. 2019, 82, 91–97. [Google Scholar] [CrossRef]
  61. Kljajić, P.; Andrić, G.; Adamović, M.; Bodroža-Solarov, M.; Marković, M.; Perić, I. Laboratory assessment of insecticidal effectiveness of natural zeolite and diatomaceous earth formulations against three stored-product beetle pests. J. Stored Prod. Res. 2010, 46, 1–6. [Google Scholar] [CrossRef]
  62. Kavallieratos, N.G.; Athanassiou, C.G.; Boukouvala, M.C.; Rumbos, C.I. Acaricidal effect of three zeolite formulations on different life stages of Tyrophagus putrescentiae (Schrank) and Acarus siro L. (Sarcoptiformes: Acaridae). J. Stored Prod. Res. 2018, 78, 39–44. [Google Scholar] [CrossRef]
  63. Floros, G.D.; Kokkari, A.I.; Kouloussis, N.A.; Kantiranis, N.A.; Damos, P.; Filippidis, A.A.; Koveos, D.S. Evaluation of the Natural Zeolite Lethal Effects on Adults of the Bean Weevil Under Different Temperatures and Relative Humidity Regimes. J. Econ. Entomol. 2017, 111, 482–490. [Google Scholar] [CrossRef]
  64. Eroglu, N.; Sakka, M.K.; Emekci, M.; Athanassiou, C.G. Effects of zeolite formulations on the mortality and progeny production of Sitophilus oryzae and Oryzaephilus surinamensis at different temperature and relative humidity levels. J. Stored Prod. Res. 2019, 81, 40–45. [Google Scholar] [CrossRef]
  65. Bohinc, T.; Horvat, A.; Andrić, G.; Golić, M.P.; Kljajić, P.; Trdan, S. Natural versus synthetic zeolites for controlling the maize weevil (Sitophilus zeamais)–like Messi versus Ronaldo? J. Stored Prod. Res. 2020, 88, 101639. [Google Scholar] [CrossRef]
  66. Paponja, I.; Rozman, V.; Liška, A. Natural Formulation Based on Diatomaceous Earth and Botanicals against Stored Product Insects. Insects 2020, 11, 613. [Google Scholar] [CrossRef] [PubMed]
  67. Athanassiou, C.G.; Korunic, Z. Evaluation of two new diatomaceous earth formulations, enhanced with abamectin and bitterbarkomycin, against four stored-grain beetle species. J. Stored Prod. Res. 2007, 43, 468–473. [Google Scholar] [CrossRef]
  68. Gad, H.A.; Al-Anany, M.S.; Abdelgaleil, S.A.M. Enhancement the efficacy of spinosad for the control Sitophilus oryzae by combined application with diatomaceous earth and Trichoderma harzianum. J. Stored Prod. Res. 2020, 88, 101663. [Google Scholar] [CrossRef]
  69. Gad, H.A.; Al-Anany, M.S.M.; mohamed Sameer, W.; Al-Anany, F.S.M. Control of Acanthoscelides obtectus with Trichoderma harzianum applied alone or in combination with diatomaceous earth on a stored common bean. Plant Prot. Sci. 2020, 56, 107–115. [Google Scholar]
  70. Wakil, W.; Riasat, T.; Ghazanfar, M.U.; Kwon, Y.J.; Shaheen, F.A. Aptness of Beauveria bassiana and enhanced diatomaceous earth (DEBBM) for control of Rhyzopertha dominica F. Entomol. Res. 2011, 41, 233–241. [Google Scholar] [CrossRef]
  71. Akbar, W.; Lord, J.C.; Nechols, J.R.; Howard, R.W. Diatomaceous Earth Increases the Efficacy of Beauveria bassiana Against Tribolium castaneum Larvae and Increases Conidia Attachment. J. Econ. Entomol. 2004, 97, 273–280. [Google Scholar] [CrossRef]
  72. Yang, F.-L.; Liang, G.-W.; Xu, Y.-J.; Lu, Y.-Y.; Zeng, L. Diatomaceous earth enhances the toxicity of garlic, Allium sativum, essential oil against stored-product pests. J. Stored Prod. Res. 2010, 46, 118–123. [Google Scholar] [CrossRef]
  73. Mohale, S.; Allotey, J.; Siame, B. Control of Tribolium confusum J. du Val by diatomaceous earth (Protect It™) on stored groundnut (Arachis hypogaea) and aspergillus flavus link spore dispersal. Afr. J. Food Agric. Nutr. Dev. 2010, 10, 2678–2694. [Google Scholar] [CrossRef]
  74. Di Gregorio, M.C.; Neeff, D.V.d.; Jager, A.V.; Corassin, C.H.; Carão, Á.C.d.P.; Albuquerque, R.d.; Azevedo, A.C.d.; Oliveira, C.A.F. Mineral adsorbents for prevention of mycotoxins in animal feeds. Toxin Rev. 2014, 33, 125–135. [Google Scholar] [CrossRef]
  75. Wielogórska, E.; MacDonald, S.; Elliott, C. A review of the efficacy of mycotoxin detoxifying agents used in feed in light of changing global environment and legislation. World Mycotoxin J. 2016, 9, 419–433. [Google Scholar] [CrossRef]
  76. Khaled, W.; Ben Fekih, I.; Chaieb, I.; Souissi, R.; Harbaoui, I.; Boukhris-Bouhachem, S. Insecticidal activity assessment of Thymus capitatus essential oils in combination with natural abrasives against Myzus persicae. Tunis. J. Plant Prot. 2017, 12, 49–59. [Google Scholar]
  77. Kilpinen, O.; Steenberg, T. Inert dusts and their effects on the poultry red mite (Dermanyssus gallinae). In Control of Poultry Mites (Dermanyssus); Springer: Berlin, Germany, 2009; pp. 51–62. [Google Scholar]
  78. Ulrichs, C.; Krause, F.; Rocksch, T.; Goswami, A.; Mewis, I. Electrostatic application of inert silica dust based insecticides onto plant surfaces. Commun. Agric. Appl. Biol. Sci. 2006, 71, 171–178. [Google Scholar] [PubMed]
  79. Wakil, W.; Ghazanfar, M.U.; Kwon, Y.J.; Ullah, E.; Islam, S.; Ali, K. Testing Paecilomyces lilacinus, diatomaceous earth and Azadirachta indica alone and in combination against cotton aphid (Aphis gossypii Glover)(Insecta: Homoptera: Aphididae). Afr. J. Biotechnol. 2012, 11, 821–828. [Google Scholar]
  80. Singh, B.; Singh, V. Laboratory and Field Studies Demonstrating the Insecticidal Potential of Diatomaceous Earth against Wheat Aphids in Rice-wheat Cropping System of Punjab (India). Cereal Res. Commun. 2016, 44, 435–443. [Google Scholar] [CrossRef] [Green Version]
  81. De Smedt, C.; Someus, E.; Spanoghe, P. Potential and actual uses of zeolites in crop protection. Pest Manag. Sci. 2015, 71, 1355–1367. [Google Scholar] [CrossRef]
  82. Speiser, B.; Tamm, L. Regulation of plant protection in organic farming. In Regulation of Biological Control Agents; Springer: Berlin, Germany, 2011; pp. 113–125. [Google Scholar]
  83. Ozbahce, A.; Tari, A.F.; Gönülal, E.; Simsekli, N.; Padem, H. The effect of zeolite applications on yield components and nutrient uptake of common bean under water stress. Arch. Agron. Soil Sci. 2015, 61, 615–626. [Google Scholar] [CrossRef]
  84. Zheng, J.; Chen, T.; Wu, Q.; Yu, J.; Chen, W.; Chen, Y.; Siddique, K.H.M.; Meng, W.; Chi, D.; Xia, G. Effect of zeolite application on phenology, grain yield and grain quality in rice under water stress. Agric. Water Manag. 2018, 206, 241–251. [Google Scholar] [CrossRef]
  85. Jankauskiene, J.; Brazaityte, A.; Kairiene, V.V.; Zalatorius, V. Effects of peat and peat-zeolite substrates on quality, growth indices of cucumber seedlings and crop productivity. Acta Sci. Pol.-Hortorum Cultus 2019, 18, 161–170. [Google Scholar] [CrossRef]
  86. Ramesh, K.; Reddy, D.D. Zeolites and their potential uses in agriculture. In Advances in Agronomy; Elsevier: Amsterdam, The Netherlands, 2011; Volume 113, pp. 219–241. [Google Scholar]
  87. Nur Aainaa, H.; Haruna Ahmed, O.; Ab Majid, N.M. Effects of clinoptilolite zeolite on phosphorus dynamics and yield of Zea Mays L. cultivated on an acid soil. PLoS ONE 2018, 13, e0204401. [Google Scholar] [CrossRef]
  88. Baghbani-Arani, A.; Modarres-Sanavy, S.A.M.; Mashhadi-Akbar-Boojar, M.; Mokhtassi-Bidgoli, A. Towards improving the agronomic performance, chlorophyll fluorescence parameters and pigments in fenugreek using zeolite and vermicompost under deficit water stress. Ind. Crop. Prod. 2017, 109, 346–357. [Google Scholar] [CrossRef]
  89. Hazrati, S.; Tahmasebi-Sarvestani, Z.; Mokhtassi-Bidgoli, A.; Modarres-Sanavy, S.A.M.; Mohammadi, H.; Nicola, S. Effects of zeolite and water stress on growth, yield and chemical compositions of Aloe vera L. Agric. Water Manag. 2017, 181, 66–72. [Google Scholar] [CrossRef]
  90. Noori, M.; Zendehdel, M.; Ahmadi, A. Using natural zeolite for the improvement of soil salinity and crop yield. Toxicol. Environ. Chem. 2006, 88, 77–84. [Google Scholar] [CrossRef]
  91. Bybordi, A.; Saadat, S.; Zargaripour, P. The effect of zeolite, selenium and silicon on qualitative and quantitative traits of onion grown under salinity conditions. Arch. Agron. Soil Sci. 2018, 64, 520–530. [Google Scholar] [CrossRef]
  92. Saeed, Z.; Naveed, M.; Imran, M.; Bashir, M.A.; Sattar, A.; Mustafa, A.; Hussain, A.; Xu, M. Combined use of Enterobacter sp. MN17 and zeolite reverts the adverse effects of cadmium on growth, physiology and antioxidant activity of Brassica napus. PLoS ONE 2019, 14, e0213016. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  93. Farouk, S.; Al-Amri, S.M. Ameliorative roles of melatonin and/or zeolite on chromium-induced leaf senescence in marjoram plants by activating antioxidant defense, osmolyte accumulation, and ultrastructural modification. Ind. Crop. Prod. 2019, 142, 111823. [Google Scholar] [CrossRef]
  94. Shahbaz, A.K.; Adnan Ramzani, P.M.; Saeed, R.; Turan, V.; Iqbal, M.; Lewińska, K.; Abbas, F.; Saqib, M.; Tauqeer, H.M.; Iqbal, M.; et al. Effects of biochar and zeolite soil amendments with foliar proline spray on nickel immobilization, nutritional quality and nickel concentrations in wheat. Ecotoxicol. Environ. Safe. 2019, 173, 182–191. [Google Scholar] [CrossRef]
  95. do Nascimento, C.W.A.; de Souza Nunes, G.H.; Preston, H.A.F.; da Silva, F.B.V.; Preston, W.; Loureiro, F.L.C. Influence of Silicon Fertilization on Nutrient Accumulation, Yield and Fruit Quality of Melon Grown in Northeastern Brazil. Silicon 2020, 12, 937–943. [Google Scholar] [CrossRef]
  96. Alsar, Z.; Duskinova, B.; Insepov, Z. New Sorption Properties of Diatomaceous Earth for Water Desalination and Reducing Salt Stress of Plants. Eurasian Chem.-Technol. J. 2020, 22, 89–97. [Google Scholar] [CrossRef]
  97. Bello, O.S.; Adegoke, K.A.; Oyewole, R.O. Insights into the Adsorption of Heavy Metals from Wastewater using Diatomaceous Earth. Sep. Sci. Technol. 2014, 49, 1787–1806. [Google Scholar] [CrossRef]
  98. Sosa, G.L.; Fernández Morantes, C.; Flores, F.M.; Torres Sánchez, R.M.; Zalts, A.; Ramirez, S.A. Characterization of diatomaceous earth modified by organic ligands for enhanced zinc adsorption. J. Environ. Chem. Eng. 2019, 7, 103197. [Google Scholar] [CrossRef]
  99. Miretzky, P.; Muñoz, C.; Cantoral-Uriza, E. Cd2+ adsorption on alkaline-pretreated diatomaceous earth: Equilibrium and thermodynamic studies. Environ. Chem. Lett. 2011, 9, 55–63. [Google Scholar] [CrossRef]
  100. Salih, S.S.; Ghosh, T.K. Highly efficient competitive removal of Pb(II) and Ni(II) by chitosan/diatomaceous earth composite. J. Environ. Chem. Eng. 2018, 6, 435–443. [Google Scholar] [CrossRef]
  101. du Jardin, P. Plant biostimulants: Definition, concept, main categories and regulation. Sci. Hortic. 2015, 196, 3–14. [Google Scholar] [CrossRef] [Green Version]
  102. Ciarkowska, K.; Sołek-Podwika, K.; Filipek-Mazur, B.; Tabak, M. Comparative effects of lignite-derived humic acids and FYM on soil properties and vegetable yield. Geoderma 2017, 303, 85–92. [Google Scholar] [CrossRef]
  103. Li, H.; Shi, W.-Y.; Shao, H.-B.; Shao, M.-A. The remediation of the lead-polluted garden soil by natural zeolite. J. Hazard. Mater. 2009, 169, 1106–1111. [Google Scholar] [CrossRef] [PubMed]
  104. Kaya, C.; Şenbayram, M.; Akram, N.A.; Ashraf, M.; Alyemeni, M.N.; Ahmad, P. Sulfur-enriched leonardite and humic acid soil amendments enhance tolerance to drought and phosphorus deficiency stress in maize (Zea mays L.). Sci. Rep. 2020, 10, 1–13. [Google Scholar] [CrossRef] [Green Version]
  105. Yu, Y.; Wan, Y.; Wang, Q.; Li, H. Effect of humic acid-based amendments with foliar application of and Se on Cd accumulation in tobacco. Ecotoxicol. Environ. Safe. 2017, 138, 286–291. [Google Scholar] [CrossRef]
  106. Kumar, S.; Srivastava, R.; Koh, J. Utilization of zeolites as CO2 capturing agents: Advances and future perspectives. J. Co2 Util. 2020, 41, 101251. [Google Scholar] [CrossRef]
  107. Tang, X.; Houzé de l’Aulnoit, S.; Buelow, M.T.; Slack, J.; Singer, B.C.; Destaillats, H. Performance of a CO2 sorbent for indoor air cleaning applications: Effects of environmental conditions, sorbent aging, and adsorption of co-occurring formaldehyde. Indoor Air 2020. [Google Scholar] [CrossRef]
  108. Mphande, W.; Kettlewell, P.S.; Grove, I.G.; Farrell, A.D. The potential of antitranspirants in drought management of arable crops: A review. Agric. Water Manag. 2020, 236, 18. [Google Scholar] [CrossRef]
  109. Brito, C.; Dinis, L.T.; Luzio, A.; Silva, E.; Goncalves, A.; Meijon, M.; Escandon, M.; Arrobas, M.; Rodrigues, M.A.; Moutinho-Pereira, J.; et al. Kaolin and salicylic acid alleviate summer stress in rainfed olive orchards by modulation of distinct physiological and biochemical responses. Sci. Hortic. 2019, 246, 201–211. [Google Scholar] [CrossRef] [Green Version]
  110. Gullo, G.; Dattola, A.; Vonella, V.; Zappia, R. Effects of two reflective materials on gas exchange, yield, and fruit quality of sweet orange tree Citrus sinensis (L.) Osb. Eur. J. Agron. 2020, 118, 9. [Google Scholar] [CrossRef]
  111. Jifon, J.L.; Syvertsen, J.P. Kaolin particle film applications can increase photosynthesis and water use efficiency of ‘Ruby red’ grapefruit leaves. J. Am. Soc. Hortic. Sci. 2003, 128, 107–112. [Google Scholar] [CrossRef] [Green Version]
  112. Glenn, D.M.; Cooley, N.; Walker, R.; Clingeleffer, P.; Shellie, K. Impact of Kaolin Particle Film and Water Deficit on Wine Grape Water Use Efficiency and Plant Water Relations. Hortscience 2010, 45, 1178–1187. [Google Scholar] [CrossRef]
  113. Mucha-Pelzer, T.; Mewis, I.; Ulrichs, C. Response of glucosinolate and flavonoid contents and composition of Brassica rapa ssp. chinensis (L.) Hanelt to silica formulations used as insecticides. J. Agric. Food Chem. 2010, 58, 12473–12480. [Google Scholar] [CrossRef]
  114. Garrido, A.; Serodio, J.; De Vos, R.; Conde, A.; Cunha, A. Influence of Foliar Kaolin Application and Irrigation on Photosynthetic Activity of Grape Berries. Agronomy 2019, 9, 18. [Google Scholar] [CrossRef] [Green Version]
  115. Frioni, T.; Saracino, S.; Squeri, C.; Tombesi, S.; Palliotti, A.; Sabbatini, P.; Magnanini, E.; Poni, S. Understanding kaolin effects on grapevine leaf and whole-canopy physiology during water stress and re-watering. J. Plant Physiol. 2019, 242, 12. [Google Scholar] [CrossRef]
  116. Brito, C.; Dinis, L.T.; Moutinho-Pereira, J.; Correia, C. Kaolin, an emerging tool to alleviate the effects of abiotic stresses on crop performance. Sci. Hortic. 2019, 250, 310–316. [Google Scholar] [CrossRef]
  117. Bulgari, R.; Franzoni, G.; Ferrante, A. Biostimulants Application in Horticultural Crops under Abiotic Stress Conditions. Agronomy 2019, 9, 30. [Google Scholar] [CrossRef] [Green Version]
  118. Oljira, A.M.; Hussain, T.; Waghmode, T.R.; Zhao, H.; Sun, H.; Liu, X.; Wang, X.; Liu, B. Trichoderma Enhances Net Photosynthesis, Water Use Efficiency, and Growth of Wheat (Triticum aestivum L.) under Salt Stress. Microorganisms 2020, 8, 1565. [Google Scholar] [CrossRef]
  119. Şesan, T.E.; Oancea, A.O.; Ştefan, L.M.; Mănoiu, V.S.; Ghiurea, M.; Răut, I.; Constantinescu-Aruxandei, D.; Toma, A.; Savin, S.; Bira, A.F. Effects of Foliar Treatment with a Trichoderma Plant Biostimulant Consortium on Passiflora caerulea L. Yield and Quality. Microorganisms 2020, 8, 123. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  120. Santaniello, A.; Scartazza, A.; Gresta, F.; Loreti, E.; Biasone, A.; Di Tommaso, D.; Piaggesi, A.; Perata, P. Ascophyllum nodosum seaweed extract alleviates drought stress in Arabidopsis by affecting photosynthetic performance and related gene expression. Front. Plant Sci. 2017, 8, 1362. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  121. Dima, S.-O.; Neamțu, C.; Desliu-Avram, M.; Ghiurea, M.; Capra, L.; Radu, E.; Stoica, R.; Faraon, V.-A.; Zamfiropol-Cristea, V.; Constantinescu-Aruxandei, D. Plant Biostimulant Effects of Baker’s Yeast Vinasse and Selenium on Tomatoes through Foliar Fertilization. Agronomy 2020, 10, 133. [Google Scholar] [CrossRef] [Green Version]
  122. Gaur, S.; Kumar, J.; Kumar, D.; Chauhan, D.K.; Prasad, S.M.; Srivastava, P.K. Fascinating impact of silicon and silicon transporters in plants: A review. Ecotoxicol. Environ. Safe. 2020, 202, 12. [Google Scholar] [CrossRef]
  123. Pichyangkura, R.; Chadchawan, S. Biostimulant activity of chitosan in horticulture. Sci. Hortic. 2015, 196, 49–65. [Google Scholar] [CrossRef]
  124. Paul, K.; Sorrentino, M.; Lucini, L.; Rouphael, Y.; Cardarelli, M.; Bonini, P.; Moreno, M.B.M.; Reynaud, H.; Canaguier, R.; Trtilek, M.; et al. A Combined Phenotypic and Metabolomic Approach for Elucidating the Biostimulant Action of a Plant-Derived Protein Hydrolysate on Tomato Grown Under Limited Water Availability. Front. Plant Sci. 2019, 10, 18. [Google Scholar] [CrossRef]
  125. Ye, Y.; Medina-Velo, I.A.; Cota-Ruiz, K.; Moreno-Olivas, F.; Gardea-Torresdey, J.L. Can abiotic stresses in plants be alleviated by manganese nanoparticles or compounds? Ecotoxicol. Environ. Safe. 2019, 184, 109671. [Google Scholar] [CrossRef]
  126. Roomi, S.; Masi, A.; Conselvan, G.B.; Trevisan, S.; Quaggiotti, S.; Pivato, M.; Arrigoni, G.; Yasmin, T.; Carletti, P. Protein Profiling of Arabidopsis Roots Treated With Humic Substances: Insights Into the Metabolic and Interactome Networks. Front. Plant Sci. 2018, 9, 19. [Google Scholar] [CrossRef] [Green Version]
  127. Hidangmayum, A.; Dwivedi, P.; Katiyar, D.; Hemantaranjan, A. Application of chitosan on plant responses with special reference to abiotic stress. Physiol. Mol. Biol. Plants 2019, 25, 313–326. [Google Scholar] [CrossRef]
  128. Shukla, P.S.; Mantin, E.G.; Adil, M.; Bajpai, S.; Critchley, A.T.; Prithiviraj, B. Ascophyllum nodosum-Based Biostimulants: Sustainable Applications in Agriculture for the Stimulation of Plant Growth, Stress Tolerance, and Disease Management. Front. Plant Sci. 2019, 10, 22. [Google Scholar] [CrossRef] [Green Version]
  129. Kerchev, P.; van der Meer, T.; Sujeeth, N.; Verlee, A.; Stevens, C.V.; Van Breusegem, F.; Gechev, T. Molecular priming as an approach to induce tolerance against abiotic and oxidative stresses in crop plants. Biotechnol. Adv. 2020, 40, 107503. [Google Scholar] [CrossRef] [PubMed]
  130. Dietz, K.J.; Turkan, I.; Krieger-Liszkay, A. Redox- and Reactive Oxygen Species-Dependent Signaling into and out of the Photosynthesizing Chloroplast. Plant Physiol. 2016, 171, 1541–1550. [Google Scholar] [CrossRef] [PubMed]
  131. Guntzer, F.; Keller, C.; Meunier, J.D. Benefits of plant silicon for crops: A review. Agron. Sustain. Dev. 2012, 32, 201–213. [Google Scholar] [CrossRef] [Green Version]
  132. Katz, O. Beyond grasses: The potential benefits of studying silicon accumulation in non-grass species. Front. Plant Sci. 2014, 5, 3. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  133. Putra, R.; Powell, J.R.; Hartley, S.E.; Johnson, S.N. Is it time to include legumes in plant silicon research? Funct. Ecol. 2020, 34, 1142–1157. [Google Scholar] [CrossRef]
  134. Johnson, S.N.; Ryalls, J.M.; Gherlenda, A.N.; Frew, A.; Hartley, S.E. Benefits from below: Silicon supplementation maintains legume productivity under predicted climate change scenarios. Front. Plant Sci. 2018, 9, 202. [Google Scholar] [CrossRef] [Green Version]
  135. Mandlik, R.; Thakral, V.; Raturi, G.; Shinde, S.; Nikolić, M.; Tripathi, D.K.; Sonah, H.; Deshmukh, R. Significance of silicon uptake, transport, and deposition in plants. J. Exp. Bot. 2020. [Google Scholar] [CrossRef]
  136. Coskun, D.; Deshmukh, R.; Sonah, H.; Menzies, J.G.; Reynolds, O.; Ma, J.F.; Kronzucker, H.J.; Bélanger, R.R. The controversies of silicon’s role in plant biology. New Phytol. 2019, 221, 67–85. [Google Scholar] [CrossRef]
  137. Savvas, D.; Ntatsi, G. Biostimulant activity of silicon in horticulture. Sci. Hortic. 2015, 196, 66–81. [Google Scholar] [CrossRef]
  138. Ma, J.F. Role of silicon in enhancing the resistance of plants to biotic and abiotic stresses. Soil Sci. Plant Nutr. 2004, 50, 11–18. [Google Scholar] [CrossRef]
  139. Cooke, J.; Leishman, M.R. Consistent alleviation of abiotic stress with silicon addition: A meta-analysis. Funct. Ecol. 2016, 30, 1340–1357. [Google Scholar] [CrossRef]
  140. Etesami, H.; Jeong, B.R. Silicon (Si): Review and future prospects on the action mechanisms in alleviating biotic and abiotic stresses in plants. Ecotoxicol. Environ. Safe. 2018, 147, 881–896. [Google Scholar] [CrossRef] [PubMed]
  141. Neu, S.; Schaller, J.; Dudel, E.G. Silicon availability modifies nutrient use efficiency and content, C:N:P stoichiometry, and productivity of winter wheat (Triticum aestivum L.). Sci. Rep. 2017, 7, 8. [Google Scholar] [CrossRef] [PubMed]
  142. Liang, Y.C.; Wong, J.W.C.; Wei, L. Silicon-mediated enhancement of cadmium tolerance in maize (Zea mays L.) grown in cadmium contaminated soil. Chemosphere 2005, 58, 475–483. [Google Scholar] [CrossRef] [PubMed]
  143. Bhat, J.A.; Shivaraj, S.M.; Singh, P.; Navadagi, D.B.; Tripathi, D.K.; Dash, P.K.; Solanke, A.U.; Sonah, H.; Deshmukh, R. Role of Silicon in Mitigation of Heavy Metal Stresses in Crop Plants. Plants-Basel 2019, 8, 20. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  144. Haynes, R.J. A contemporary overview of silicon availability in agricultural soils. J. Plant Nutr. Soil Sci. 2014, 177, 831–844. [Google Scholar] [CrossRef]
  145. Ma, J.F.; Yamaji, N. Functions and transport of silicon in plants. Cell. Mol. Life Sci. 2008, 65, 3049–3057. [Google Scholar] [CrossRef]
  146. Ma, J.F.; Yamaji, N. Silicon uptake and accumulation in higher plants. Trends Plant Sci. 2006, 11, 392–397. [Google Scholar] [CrossRef]
  147. Costa, R.R.; Moraes, J.C.; DaCosta, R.R. Feeding behaviour of the greenbug Schizaphis graminum on wheat plants treated with imidacloprid and/or silicon. J. Appl. Entomol. 2011, 135, 115–120. [Google Scholar] [CrossRef]
  148. Reynolds, O.L.; Keeping, M.G.; Meyer, J.H. Silicon-augmented resistance of plants to herbivorous insects: A review. Ann. Appl. Biol. 2009, 155, 171–186. [Google Scholar] [CrossRef]
  149. Massey, F.P.; Ennos, A.R.; Hartley, S.E. Herbivore specific induction of silica-based plant defences. Oecologia 2007, 152, 677–683. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  150. Muneer, S.; Park, Y.G.; Manivannan, A.; Soundararajan, P.; Jeong, B.R. Physiological and Proteomic Analysis in Chloroplasts of Solanum lycopersicum L. under Silicon Efficiency and Salinity Stress. Int. J. Mol. Sci. 2014, 15, 21803–21824. [Google Scholar] [CrossRef] [PubMed]
  151. Shi, Y.; Wang, Y.C.; Flowers, T.J.; Gong, H.J. Silicon decreases chloride transport in rice (Oryza sativa L.) in saline conditions. J. Plant Physiol. 2013, 170, 847–853. [Google Scholar] [CrossRef] [PubMed]
  152. Yeo, A.R.; Flowers, S.A.; Rao, G.; Welfare, K.; Senanayake, N.; Flowers, T.J. Silicon reduces sodium uptake in rice (Oryza sativa L.) in saline conditions and this is accounted for by a reduction in the transpirational bypass flow. Plant Cell Environ. 1999, 22, 559–565. [Google Scholar] [CrossRef]
  153. Tahir, M.A.; Rahmatullah; Aziz, T.; Ashraf, M.; Kanwal, S.; Maqsood, M.A. Beneficial effects of silicon in wheat (Triticum aestivum L.) under salinity stress. Pak. J. Bot. 2006, 38, 1715–1722. [Google Scholar]
  154. Liang, Y.C.; Sun, W.C.; Zhu, Y.G.; Christie, P. Mechanisms of silicon-mediated alleviation of abiotic stresses in higher plants: A review. Environ. Pollut. 2007, 147, 422–428. [Google Scholar] [CrossRef] [Green Version]
  155. Van Bockhaven, J.; De Vleesschauwer, D.; Hofte, M. Towards establishing broad-spectrum disease resistance in plants: Silicon leads the way. J. Exp. Bot. 2013, 64, 1281–1293. [Google Scholar] [CrossRef]
  156. Thaler, J.S.; Humphrey, P.T.; Whiteman, N.K. Evolution of jasmonate and salicylate signal crosstalk. Trends Plant Sci. 2012, 17, 260–270. [Google Scholar] [CrossRef]
  157. Robert-Seilaniantz, A.; Grant, M.; Jones, J.D.G. Hormone Crosstalk in Plant Disease and Defense: More Than Just JASMONATE-SALICYLATE Antagonism. In Annual Review of Phytopathology, Vol 49; VanAlfen, N.K., Bruening, G., Leach, J.E., Eds.; Annual Reviews: Palo Alto, CA, USA, 2011; Volume 49, pp. 317–343. [Google Scholar]
  158. Hauser, F.; Waadt, R.; Schroeder, J.I. Evolution of Abscisic Acid Synthesis and Signaling Mechanisms. Curr. Biol. 2011, 21, R346–R355. [Google Scholar] [CrossRef] [Green Version]
  159. Baxter, A.; Mittler, R.; Suzuki, N. ROS as key players in plant stress signalling. J. Exp. Bot. 2014, 65, 1229–1240. [Google Scholar] [CrossRef]
  160. Gross, F.; Durner, J.; Gaupels, F. Nitric oxide, antioxidants and prooxidants in plant defence responses. Front. Plant Sci. 2013, 4, 15. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  161. Guerriero, G.; Hausman, J.-F.; Legay, S. Silicon and the plant extracellular matrix. Front. Plant Sci. 2016, 7. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  162. Le, D.M.; Sørensen, H.R.; Knudsen, N.O.; Meyer, A.S. Implications of silica on biorefineries – interactions with organic material and mineral elements in grasses. Biofuelsbioprod. Biorefining 2015, 9, 109–121. [Google Scholar] [CrossRef]
  163. Epstein, E. Silicon. Annu. Rev. Plant Physiol. Plant Molec. Biol. 1999, 50, 641–664. [Google Scholar] [CrossRef]
  164. Patwardhan, S.V.; Tilburey, G.E.; Perry, C.C. Interactions of Amines with Silicon Species in Undersaturated Solutions Leads to Dissolution and/or Precipitation of Silica. Langmuir 2011, 27, 15135–15145. [Google Scholar] [CrossRef] [PubMed]
  165. Wedepohl, K.H. The composition of the continental-crust. Geochim. Cosmochim. Acta 1995, 59, 1217–1232. [Google Scholar] [CrossRef]
  166. Sommer, M.; Kaczorek, D.; Kuzyakov, Y.; Breuer, J. Silicon pools and fluxes in soils and landscapes—A review. J. Plant Nutr. Soil Sci. -Z. Fur Pflanzenernahr. Und Bodenkd. 2006, 169, 310–329. [Google Scholar] [CrossRef]
  167. Joergensen, R.G.; Scholle, G.A.; Wolters, V. Dynamics of mineral components in the forest floor of an acidic beech (Fagus sylvatica L.) forest. Eur. J. Soil Biol. 2009, 45, 285–289. [Google Scholar] [CrossRef]
  168. Hammer, E.C.; Nasr, H.; Pallon, J.; Olsson, P.A.; Wallander, H. Elemental composition of arbuscular mycorrhizal fungi at high salinity. Mycorrhiza 2011, 21, 117–129. [Google Scholar] [CrossRef]
  169. Bidle, K.D.; Azam, F. Accelerated dissolution of diatom silica by marine bacterial assemblages. Nature 1999, 397, 508–512. [Google Scholar] [CrossRef]
  170. Demadis, K.D.; Mavredaki, E.; Somara, M. Additive-Driven Dissolution Enhancement of Colloidal Silica. 2. Environmentally Friendly Additives and Natural Products. Ind. Eng. Chem. Res. 2011, 50, 13866–13876. [Google Scholar] [CrossRef]
  171. Belton, D.; Patwardhan, S.V.; Perry, C.C. Putrescine homologues control silica morphogenesis by electrostatic interactions and the hydrophobic effect. Chem. Commun. 2005, 3475–3477. [Google Scholar] [CrossRef] [PubMed]
  172. Belton, D.J.; Patwardhan, S.V.; Perry, C.C. Spermine, spermidine and their analogues generate tailored silicas. J. Mater. Chem. 2005, 15, 4629–4638. [Google Scholar] [CrossRef]
  173. Temirov, Y.V.; Esikova, T.Z.; Kashparov, I.A.; Balashova, T.A.; Vinokurov, L.M.; Alakhov, Y.B. A catecholic siderophore produced by the thermoresistant Bacillus licheniformis VK21 strain. Russ. J. Bioorgan. Chem. 2003, 29, 542–549. [Google Scholar] [CrossRef]
  174. Venturi, V.; Zennaro, F.; Degrassi, G.; Okeke, B.C.; Bruschi, C.V. Genetics of ferulic acid bioconversion to protocatechuic acid in plant-growth-promoting Pseudomonas putida WCS358. Microbiology 1998, 144, 965–973. [Google Scholar] [CrossRef] [Green Version]
  175. Tiwari, S.; Singh, P.; Tiwari, R.; Meena, K.K.; Yandigeri, M.; Singh, D.P.; Arora, D.K. Salt-tolerant rhizobacteria-mediated induced tolerance in wheat (Triticum aestivum) and chemical diversity in rhizosphere enhance plant growth. Biol. Fertil. Soils 2011, 47, 907–916. [Google Scholar] [CrossRef]
  176. Cassán, F.; Maiale, S.; Masciarelli, O.; Vidal, A.; Luna, V.; Ruiz, O. Cadaverine production by Azospirillum brasilense and its possible role in plant growth promotion and osmotic stress mitigation. Eur. J. Soil Biol. 2009, 45, 12–19. [Google Scholar] [CrossRef]
  177. Nassar, A.H.; El-Tarabily, K.A.; Sivasithamparam, K. Growth promotion of bean (Phaseolus vulgaris L.) by a polyamine-producing isolate of Streptomyces griseoluteus. Plant Growth Regul. 2003, 40, 97–106. [Google Scholar] [CrossRef]
  178. Xie, S.S.; Wu, H.J.; Zang, H.Y.; Wu, L.M.; Zhu, Q.Q.; Gao, X.W. Plant Growth Promotion by Spermidine-Producing Bacillus subtilis OKB105. Mol. Plant-Microbe Interact. 2014, 27, 655–663. [Google Scholar] [CrossRef] [Green Version]
  179. Prentice, P. Efficacy of silica in increasing fields in Marocco. In Proceedings of the 7th International Conference on Silicon in Agriculture, Bengaluru, India, 24–28 October 2017; pp. 24–28. [Google Scholar]
  180. Encina Oliva, K.M.; Araújo do Nascimento, C.W.; Vieira da Silva, F.B.; Muniz Araújo, P.R.; Almeida de Oliveira, E.C.; Feitosa, M.M.; Vieira Lima, L.H. Biomass and concentration of nutrients and silicon in sugarcane grown on soil fertilized with diatomite. Braz. J. Agric. Sci./Rev. Bras. De Ciências Agrárias 2020, 15, 1–7. [Google Scholar]
  181. Kadalli, G.; Rudresha, B.; Prakash, N. Effect of diatomite as a silicon source on growth, yield and quality of potato. In Proceedings of the 7th International Conference on Silicon in Agriculture, Bengaluru, India, 24–28 October 2017; pp. 24–28. [Google Scholar]
  182. Barão, L.; Teixeira, R.; Vandevenne, F.; Ronchi, B.; Unzué-Belmonte, D.; Struyf, E. Silicon Mobilization in Soils: The Broader Impact of Land Use. Silicon 2019, 1, 1–10. [Google Scholar] [CrossRef]
  183. Carey, J.C.; Fulweiler, R.W. Human appropriation of biogenic silicon–the increasing role of agriculture. Funct. Ecol. 2016, 30, 1331–1339. [Google Scholar] [CrossRef] [Green Version]
  184. Kuroda, K.; Kurashita, H.; Arata, T.; Miyata, A.; Kawazoe, M.; Nobu, M.K.; Narihiro, T.; Ohike, T.; Hatamoto, M.; Maki, S.; et al. Influence of Green Tuff Fertilizer Application on Soil Microorganisms, Plant Growth, and Soil Chemical Parameters in Green Onion (Allium fistulosum L.) Cultivation. Agronomy 2020, 10, 929. [Google Scholar] [CrossRef]
  185. Aguirre, L.E.; Ouyang, L.; Elfwing, A.; Hedblom, M.; Wulff, A.; Inganäs, O. Diatom frustules protect DNA from ultraviolet light. Sci. Rep. 2018, 8, 1–6. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  186. Goessling, J.W.; Su, Y.; Cartaxana, P.; Maibohm, C.; Rickelt, L.F.; Trampe, E.C.; Walby, S.L.; Wangpraseurt, D.; Wu, X.; Ellegaard, M. Structure-based optics of centric diatom frustules: Modulation of the in vivo light field for efficient diatom photosynthesis. New Phytol. 2018, 219, 122–134. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  187. Glenn, D.; Puterka, G.; Vanderzwet, T.; Byers, R.; Feldhake, C. Hydrophobic particle films: A new paradigm for suppression of arthropod pests and plant diseases. J. Econ. Entomol. 1999, 92, 759–771. [Google Scholar] [CrossRef] [Green Version]
  188. Glenn, D.M.; Puterka, G.J. Particle films: A new technology for agriculture. Hortic. Rev. 2005, 31, 1–44. [Google Scholar]
  189. Domenico, P. Particle films: Chabazitic zeolites with added microorganisms in the protection and growth of tomato plants (Lycopersicon esculentum L.). Gsc Adv. Res. Rev. 2020, 4, 1–8. [Google Scholar] [CrossRef]
  190. Ge, W.; Du, G.; Zhang, L.; Li, Z.; Xiao, G.; Chen, B. The Time–Concentration–Mortality Responses of Western Flower Thrips, Frankliniella occidentalis, to the Synergistic Interaction of Entomopathogenic Fungus Metarhizium flavoviride, Insecticides, and Diatomaceous Earth. Insects 2020, 11, 93. [Google Scholar] [CrossRef] [Green Version]
  191. Qiu, Y.; Amirkhani, M.; Mayton, H.; Chen, Z.; Taylor, A.G. Biostimulant Seed Coating Treatments to Improve Cover Crop Germination and Seedling Growth. Agronomy 2020, 10, 154. [Google Scholar] [CrossRef] [Green Version]
Agronomy 10 01791 g001 550
Figure 1. The common features of siliceous natural nanomaterials which are determinant for their application as plant protectant, plant biostimulants, and soil improvers.
Figure 1. The common features of siliceous natural nanomaterials which are determinant for their application as plant protectant, plant biostimulants, and soil improvers.
Agronomy 10 01791 g001
Agronomy 10 01791 g002 550
Figure 2. The relationship between organic fertilizers/soil improvers and the organic plant biostimulants and the similarities between their effects on plants and those exerted by the soil improvers based on siliceous natural nanomaterials.
Figure 2. The relationship between organic fertilizers/soil improvers and the organic plant biostimulants and the similarities between their effects on plants and those exerted by the soil improvers based on siliceous natural nanomaterials.
Agronomy 10 01791 g002
Agronomy 10 01791 g003 550
Figure 3. Siliceous natural nanomaterials as soluble silicon sources for plants. Diatomaceous earth, formed mainly by amorphous silica, is similar to phytogenic silica and releases silicic acid by hydrolysis. Zeolites form silicic acid mainly by weathering. In the root silicon block potential toxic element uptake. In soil, the moderate mobile H4SiO4 is precipitated with immobile Al and Fe ions and generates clays. The apoplastic and symplastic soluble silicon flow sustain the silica deposition, after concentration into aerial parts. This process balances reactive oxygen species enhances plant tolerance to abiotic stress and blocks the action of pest and pathogen effectors.
Figure 3. Siliceous natural nanomaterials as soluble silicon sources for plants. Diatomaceous earth, formed mainly by amorphous silica, is similar to phytogenic silica and releases silicic acid by hydrolysis. Zeolites form silicic acid mainly by weathering. In the root silicon block potential toxic element uptake. In soil, the moderate mobile H4SiO4 is precipitated with immobile Al and Fe ions and generates clays. The apoplastic and symplastic soluble silicon flow sustain the silica deposition, after concentration into aerial parts. This process balances reactive oxygen species enhances plant tolerance to abiotic stress and blocks the action of pest and pathogen effectors.
Agronomy 10 01791 g003
Agronomy 10 01791 g004 550
Figure 4. The main effects of siliceous natural nanomaterials and the gaps in knowledge related to their effects on (micro)organisms associated to microbiocenosis delimitated by plant organs. The gaps are shown in black boxes.
Figure 4. The main effects of siliceous natural nanomaterials and the gaps in knowledge related to their effects on (micro)organisms associated to microbiocenosis delimitated by plant organs. The gaps are shown in black boxes.
Agronomy 10 01791 g004
Table
Table 1. Example of several commercial products based on diatomaceous earth.
Table 1. Example of several commercial products based on diatomaceous earth.
Commercial NameType of Diatomaceous Earth (DE)Others (Active) IngredientsDose (mg/kg)CommodityTested Insect SpeciesMortalityRef.
Celatom®
MN-51		Fresh water DE,
dimension 15 µm, 83.7% SiO2, less than 1% crystalline SiO2		none500wheat grainsSitophilus oryzae100%, after 14 days, 30 °C, 70% RH 1[49]
Tribolium castaneum100%, after 14 days, 30 °C, 70% RH 1
Rhyzopertha dominica100%, after 14 days, 30 °C, 70% RH 1
SilicoSec®Fresh water DE, dimension 8-12 µm, 92% SiO2
less than 1% crystalline SiO2		none1500Wheat flourT. castaneum100%, 32 °C, 55% RH 1[50]
1500Barley grainS. oryzae1005, after 7 days[51]
1500Maize grain>65%, after 14 days
800Wheat grainEphestia kuehniella>85%, after 14 days, 32 °C
>65%, after 14 days, 75% RH 1		[52]
900Wheat
Barley		T. castaneum>65%, after 21 days[52]
S. oryzae100%, after 21 days, 30 °C,
55% RH 1
R. dominica90%, after 21 days, 30 °C,
55% RH 1
Protect-It®Marine DE, median dimension 5.4 µm, 83.7% SiO2, less than 0.9% crystalline SiO2Silica aerogel 10%300Wheat grainT. castaneum100%, after 1 month, field test-variable temperature, 55% RH[53]
>400WheatT. castaneum100%, after 14 days, 30 °C, 65% RH 1[54]
PyriSec®Fresh water DE, dimension 8-12 µm, ~90% SiO2
less than 1% crystalline SiO2 (SilicoSec®, 95.7%)		1.2%
natural pyrethrum (25%), 3.1% piperonyl butoxide		1500peeled barleyR. dominica84.2%, 26 °C, 55% RH 1[55]
wheat, whole barley, oats, rye, triticale, rice, maize>95%, 26 °C, 55% RH 1
300wheat
barley		Oryzaephilus surinamensis100% after
7 days		[56]
900wheat
barley		T. castaneum100% after
21 days
900Wheat
barley		S. oryzae,
R. dominica		100% and
90%, 14 days
30 °C, 55% RH
DryacideTMFreshwater DE; 90% amorphous SiO2; mean particle size: 13–15 mmnone400wheatS. oryzae>95%, after 7 days, 30 °C,[57]
600T. castaneum>90%, after 14 days, 30 °C, 65% RH 1[54]
Insecto®Marine DE, median dimension 8.2 μm, 87% amorphous SiO210% food-grade bait400wheatS. oryzae96%, after 14 days, 26 °C, 57%[58]
600T. castaneum90%, after 14 days, 30 °C, 65% RH 1[54]
Perma GuardTMFreshwater DE; median dimension 93% SiO2none400wheatS. oryzae77%, after 14 days, 26 °C, 57%[58]
1000wheatT. castaneum100%, after 14 days, 30 °C, 65% RH 1[54]
1 RH—relative humidity.
Table
Table 2. Enhanced siliceous natural nanomaterials (SNNMs) efficacy as stored commodities by complementary bioactive ingredients.
Table 2. Enhanced siliceous natural nanomaterials (SNNMs) efficacy as stored commodities by complementary bioactive ingredients.
Type of SNNMsComplementary Active IngredientsDose (mg/kg)CommodityTested Insect SpeciesMortalityRef.
Diatomaceous earth (SilicoSec®
48% wt/wt)		Silica gel (24% wt/wt),
bay leaves powder (20% wt/wt), corn oil (3% wt/wt), lavender Lavandula x intermedia essential oil (2% wt/wt), dried yeast up to 100%		600wheat grainT. castaneum100%, 14 days, 28 °C, 60% RH 1[66]
S. oryzae100%, 14 days, 28 °C, 60% RH 1
R. dominica100%, 4 days, 28 °C, 60% RH 1
600barley grainT. castaneum>95%, 14 days, 28 °C, 60% RH 1
S. oryzae>95%, 14 day, 28 °C, 60% RH 1
R. dominica100%, 14 days, 28 °C, 60% RH 1
Diatomaceous earth (Celatom® MN-51)Amorphous silica gel (20%), lavandin EO, Torula yeast powder400wheat grainsS. oryzae100%, after 2 days, 28 °C, 65% RH 1[25]
Diatomaceous earth (Celatom® MN-51) Amorphous silica gel (3%), pyrethrin,
flax oil, lavandin essential oil (EO), and Torula yeast powder		125wheat grainsS. oryzae100%, after 2 days, 28 °C, 65% RH 1[25]
125R. dominica81%, after 2 days, 28 °C, 65% RH 1
100T. castaneum83%, after 6 days, 28 °C, 65% RH 1
Fresh water DE 89% amorphous SiO2, 4.0%, dimension 10 μm, crystalline silica 0.1%.Abamectin, 0.25%75wheat grainS. oryzae100%, 14 days, 30 °C, 70% RH 1[67]
150R. dominica>95%, 14 days, 30 °C, 70% RH 1
125T. castaneum100%, 14 days, 30 °C, 70% RH 1
75Cryptolestes ferrugineus100%, 14 days, 30 °C, 70% RH 1
Fresh water DE 89% amorphous SiO2, 4.0%, dimension 10 μm, crystalline silica 0.1%.Bitter bark omycin, 0.05%125wheat grainS. oryzae100%, 14 days, 30 °C, 70% RH 1[67]
75R. dominica>95%, 14 days, 30 °C, 70% RH 1
150T. castaneum100%, 14 days, 30 °C, 70% RH 1
125C. ferrugineus100%, 14 days, 30 °C, 70% RH 1
Egyptian diatomaceous earth, 46.37% SiO2Spinosad (98%), 0.5 mg/kg100wheat grainsS. oryzae100%, after 14 days, 28 °C, 65% RH 1[68]
Egyptian diatomaceous earth, 46.37% SiO2Trichoderma harzianum (Egyptian strain)800common beansAcanthoscelides obtectus>93%, after 7 days, 24 °C, 60% RH 1[69]
DEBBM, mixture of Canadian diatomaceous earth, freshwater DE
89% SiO2 and bitter barkomycin		Bitter barkomycin, 0.05%
Beauveria bassiana
6.69 × 1010 conidia		30wheat grainsR. dominica>90%, 15 days, 25 °C, 55% RH 1[70]
Marine DE, median dimension 5.4 µm, 83.7% SiO2, (Protect-It®)Beauveria bassiana. 2700 mg/kg190wheat grainsT. castaneum larvae>90%, 8 days, 26 °C, 75% RH 1[71]
Chinese diatomaceous earth, 93% SiO2Garlic essential oil (purity ≥ 90%), 20 mg/kg250rice grainT. castaneum100%, 7 days, 27 °C, 70% RH 1[72]
1 RH—relative humidity.
Table
Table 3. Effects of SNNMs applied as soil improvers.
Table 3. Effects of SNNMs applied as soil improvers.
Type of SNNMsCropType of Soil/Growth Substrate-StressSNMM Dose Main EffectRef.
Zeolites (clinoptilite)Corn, Zea maysTypic Paleudults, fine sandy clay loam280–350 kg/haImproved phosphorus dynamic and uptake [87]
ZeolitesRice,
Oryza sativa L.		Clay loam-
Drought stress		15 t/haImproved head rice rate; decreased chalk rice rate and chalkiness.[84]
ZeolitesFenugreek,
Trigonella foenum-graecum		Semi-arid area -
Drought stress		9 t/haReduced effects of draught;
Improved biological and seed yield		[88]
ZeolitesAloe vera L. (syn. Aloe barbadensis Miller) Drought stress4 and 8 g/kgReduced drought stress effects; improved plant growth and yield[89]
Zeolites (clinoptilolite)Radish,
Raphanus sativus		Growing substrate, Greenhouse experiment–Salinity stress0.06 kg/m2Reduced salt uptake by plant; increased crop yield and quality[90]
ZeolitesOnion,
Allium cepa L		Silt loam soil-Salinity stress4 and 8 t/ haDecreased number of small onion bulbs[91]
ZeolitesRapeseed, Brassica napusSoil-Cadmium (Cd)10 g/kgReduced Cd uptake by plant;
Improved plant physiology		[92]
ZeolitesMarjoram, Origanum majorana L.Chromium-contaminated soil5 g/kgAlleviation of (Cr-induced) leaf senescence[93]
ZeolitesWheat, Triticum aestivum L.Nickel (Ni)-contaminated soil100 g/kgReduced Ni uptake by plant;
Improved plant physiology 		[94]
Diatomaceous earth
(Melosira granulata)		Melon, Cucumis meloCoarse texture, low nutrient and Si content200, 400, 600, and 800 kg/ha Increased nutrient uptake and nutrient use efficiency; increased yield and quality of fruits[95]
Diatomaceous earth (biogenic silica, smectite, kaolinite and quartz), AgriPower Pvt. Ltd., AustraliaRice,
Oryza sativa L., var. JGL 1798		Acidic, Neutral and alkaline soil–drought (and salinity) stress150, 300, and 600 kg/haImproved water and nutrient-use efficiency; reduced stress effects; higher grain yield under stressed conditions; Si-uptake depending on soil type[19]
Deionized diatomaceous earth (Zalpak area)Wheat, Triticum aestivum L.Growth substrate with known mineral composition–salinity stress1 and 10 g/kgImproved plant growth and yield compared with control, both with and without salinity stress [96]
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Share and Cite

MDPI and ACS Style

Constantinescu-Aruxandei, D.; Lupu, C.; Oancea, F. Siliceous Natural Nanomaterials as Biorationals—Plant Protectants and Plant Health Strengtheners. Agronomy 2020, 10, 1791. https://doi.org/10.3390/agronomy10111791

AMA Style

Constantinescu-Aruxandei D, Lupu C, Oancea F. Siliceous Natural Nanomaterials as Biorationals—Plant Protectants and Plant Health Strengtheners. Agronomy. 2020; 10(11):1791. https://doi.org/10.3390/agronomy10111791

Chicago/Turabian Style

Constantinescu-Aruxandei, Diana, Carmen Lupu, and Florin Oancea. 2020. "Siliceous Natural Nanomaterials as Biorationals—Plant Protectants and Plant Health Strengtheners" Agronomy 10, no. 11: 1791. https://doi.org/10.3390/agronomy10111791

APA Style

Constantinescu-Aruxandei, D., Lupu, C., & Oancea, F. (2020). Siliceous Natural Nanomaterials as Biorationals—Plant Protectants and Plant Health Strengtheners. Agronomy, 10(11), 1791. https://doi.org/10.3390/agronomy10111791

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop