3.1. Mineral Content, PH and Salt Concentration
Separation of meat from the inner part of the abdomen generates post-production waste in the form of chitin shell, exoskeleton, tail and head, which, depending on the species [
27], accounts for 40–50% [
11,
28], 45–55% [
29], or up to 56% [
30,
31] of the animal. This study showed high content of N, P, K, Ca and Mg in the shrimp biowaste used for substrate preparation (
Table 1). This is concurrent with the findings of other authors [
32,
33] claiming high content of macronutrients in shrimp processing waste. These minerals form the main components of the crustacean shells [
29]. The content of individual minerals in shells depends on the crustacean species and fishing season [
34], and also on the processing method [
35]. The shrimp biowaste we used in our experiment featured high amounts of salt (
Table 1). Żurawik [
36] reported its lower salinity level of 28.2 g NaCl∙dm
−3 in a similar study. The discrepancy was probably due to different fishing time and different crustacean species. The shrimp biowaste has alkaline pH (
Table 1). This is in accordance with the publications of Evers and Carroll [
37] and Rao and Stevens [
31], who determined pH range between 7.4 and 8.0.
Supplementation of the substrate with shrimp biowaste at a dose of 5% to 15% increased the substrate salinity in the beginning of
Miscanthus sinensis and
Miscanthus × giganteus cultivation from 1.85 to 6.79 g kg
−1 (
Table 2). This was consistent with the findings of Żurawik [
36], who investigated substrate supplementation with shrimp biowaste in the cultivation of
Freesia hybrida. Dufault and Korkmaz [
38] and Dufault et al. [
39] also confirmed that sea bed sediments generated during crustacean processing and involving food debris, shells and excrements enhance the substrate salinity. Substrate supplementation with shrimp biowaste elevated its pH but differences between doses of 5% to 15% were insignificant and pH reached 7.56 and 7.64, respectively (
Table 2). Both pH and salinity decreased considerably during the growing season in the first and second year of the study (
Table 3), which according to Kotuby-Amacher et al. [
40] may affect plant growth and development.
3.2. Plant Growth and Flowering
The available literature lacks information on the use of dried waste resulting from shrimp processing as a substrate component in the cultivation of horticultural and agricultural plants. The only published study focused on the application of shrimp biowaste in the cultivation of
Freesia hybrida [
36]. However, as the species is highly sensitive to salt, the substrate was washed twice with tap water (I—1 dm
3 water per 1 dm
3 of the substrate, II—0.5 dm
3 water per 1 dm
3 of the substrate) before beginning the experiment. Matuszak and Brzóstowicz [
41] claimed that plant response to excess substrate salinity depends on the species, developmental stage, type of salt, and environmental conditions.
Our study showed different tolerance of
Miscanthus species to substrate salinity caused by supplementation of shrimp biowaste. Our findings confirmed those reported by Chen et al. [
42], who reported on considerable differences in
Miscanthus genus species tolerance to salt. Stavridou [
43] indicated that
Miscanthus ×
giganteus was more tolerant to salinity than
Miscanthus sinensis. The presented study corroborated this claim. In the first year,
Miscanthus sinensis plants exposed to any dose of shrimp biowaste showed lower height, and developed smaller number of shoots and narrower leaves than the controls (
Table 4). In
Miscanthus ×
giganteus the reduction in height, number of shoots and leaf width was only visible at 10% and 15% of shrimp biowaste dose. Żurawik [
36] described a similar pattern for
Freesia hybrida. Deterioration of the plant quality at higher doses of the biowaste that greatly increased the substrate salinity, was most probably due to their reduced water uptake capacity [
44], and consequently disruption of water and nutritional balance [
45]. At the end of the growing season, the differences in the compared vegetative traits diminished.
Miscanthus ×
giganteus plants exposed to 5% shrimp biowaste were higher, developed more shoots and wider leaves than control plants and those treated with 10% and 15% biowaste. This was concurrent with the findings of Mzabri et al. [
46], who reported that contrary to high concentrations of NaCl, its small amounts positively affect growth and development of
Crocus sativus.
Irrespective of the species, plants response to the presence of shrimp biowaste was stronger in the first than in the second year (
Table 4 and
Table 5). Kotuby-Amacher et al. [
40] also concluded that plants were more sensitive to high salinity at a seedling stage immediately after planting even though no leaf damage was found.
In the second year, the investigated species responded to the applied doses of shrimp biowaste in a different way. Increasing doses of the biowaste reduced growth of
Miscanthus sinensis (
Table 5). Substrate supplementation with low doses of bottom sediments from shrimp aquaculture and a controlled-release mineral fertilizer (Osmocote 14-6-12) enhanced rose yield in the cultivation of
Brassica oleracea var.
botrytis italica, while increasing doses caused excessive substrate salinity that limited the yield [
35]. Evaluation a month after the first emergence showed a greater number of shoots in control variant and that with 5% biowaste and smaller in 10% and 15% variants. Consecutive measurements confirmed the most abundant shoot development in plants exposed to 5% shrimp biowaste. The same patterns occurred in the experiments with
Freesia hybrida [
36]. A month after the first emergence, control plants and those growing in the substrate with the lowest dose of biowaste developed the widest leaves. Further measurements demonstrated the greatest leaf width in plants treated with the highest dose of the biowaste. We found no significant differences in
Miscanthus ×
giganteus height a month after the first emergences but during flowering and at the end of the growing season the plants treated with any dose of the biowaste were higher than the control ones. Despite high sensitivity of
Capsicum annuum to salinity, Dufault and Korkmaz [
38] obtained the greatest and highest quality yield at moderate doses of a sediment and a mineral fertilizer. Irrespective of the biowaste concentration, at the end of the growing season
Miscanthus ×
giganteus plants developed more shoots and wider leaves than control plants. The differences between the studied species were most likely due to their different sensitivity to substrate salinity, as claimed by Kotuby-Amacher et al. [
40].
A transition from vegetative to generative stage, i.e., to flowering, is one of the crucial stages of development [
47]. Regardless of the biowaste dose,
Miscanthus sinensis plants developed their inflorescences on average by 12.6 days earlier than
Miscanthus ×
giganteus ones (
Figure 1). Nuñez and Yamada [
48] ascribed this discrepancy to genetic variability of the species. Delayed flowering results in prolonged vegetative stage and increased biomass yield in C4 plants [
49]. Plant response to increasing doses of shrimp biowaste depended on the cultivated species.
Miscanthus sinensis plants began flowering on average after 136.8 days of cultivation. Addition of shrimp waste delayed their flowering in a dose dependent manner. At the highest biowaste concentration, flowering began on average by 45.5 days later than in control. Żurawik [
36] also demonstrated a delay in the commencement of generative stage with increasing substrate salinity with shrimp biowaste. A contrary situation occurred in
Miscanthus ×
giganteus. Supplementation with shrimp biowaste at 5%, 10% and 15% accelerated flowering by 2.9, 3.4 and 7.9 days, respectively. The impact of shrimp biowaste on the course of flowering was species dependent (Figure.1). Żurawik [
36] claimed the inflorescence formation time may also depend on a cultivar.
Miscanthus sinensis responded to the presence of shrimp biowaste by prolonging the stage of inflorescence formation. In the variants treated with 5% and 10% of the biowaste this stage was longer by 17.8 and 10 days, respectively. At the highest biowaste dose the plants did not complete this developmental stage during the experiment. In
Miscanthus ×
giganteus plants exposed to shrimp biowaste at 5% and 10% inflorescence formation lasted by 7.3 and 1.5 days longer, and at 15% by 12.3 days longer. According to Veatch-Blohm et al. [
50], increasing substrate salinity reduced flower duration of
Narcissus ‘Dutch Master’ and ‘Ice Follies’ by 40% to 70%.
Ornamental value of
Miscanthus species depended on the dose of shrimp biowaste (
Table 6). In
Miscanthus sinensis the most beneficial dose was 5%. Plants growing in such a substrate developed longer inflorescence shoots, greater number of lateral branching and the greatest number of inflorescence shoots as compared with control. Increasing the dose up to 15% deteriorated the ornamental value. Żurawik [
36] described identical relationships for
Freesia hybrida. In
Miscanthus ×
giganteus the most beneficial was the highest dose of biowaste, i.e., 15%. In comparison with control, plants from this variant developed a larger number of inflorescence lateral branches and inflorescence shoots of larger diameter. Irrespective of the dose and increasing substrate salinity, plants growing in the presence of shrimp biowaste produced more inflorescence shoots than the control ones. Veatch-Blohm et al. [
50] demonstrated that substrate salinity had no effects on the number of developed flowers of
Narcissus ‘Dutch Master’ and ‘Ice Follies’.
3.3. Leaf Greenness Index and Nitrogen Index
In the first year of the study, the addition of any dose of shrimp biowaste enhanced green coloration of
Miscanthus ×
giganteus leaves both during flowering and at the end of the growing season (
Table 7). A similar trend occurred in
Freesia hybrida exposed to shrimp biowaste doses increasing from 2.5% to 15% [
36]. Leaf greenness improvement confirmed the view of Pilarski [
51] that plants exposed to stress increase their chlorophyll content. According to Olszewska [
52], this is due to the reduction of cell size and thickening of leaf tissues that result in enhanced concentration of small-and high-molecular compounds. In
Miscanthus sinensis increased greenness index was only visible at 5% biowaste dose. At this concentration both species showed also higher nitrogen index at all developmental stages. Majkowska-Gadomska et al. [
53] reported that green coloration intensity depended on measurement date. In
Miscanthus sinensis it was lower at the end of the growing season than during flowering. Contrary to that, Olszewska [
54] observed growing greenness index in
Festuca pratensis and
Phleum pratense at consecutive measurement dates. We confirmed this observation in
Miscanthus ×
giganteus. At the end of the growing season, all variants cultivated in the presence of shrimp biowaste showed more intense green coloration of the leaves than during flowering. Regardless of the biowaste dose, greenness index was higher in
Miscanthus ×
giganteus than in
Miscanthus sinensis leaves. Tolerant species respond to salinity by maintaining or increasing their chlorophyll content [
55].
In the second year of the study, the experimental plants showed higher nitrogen index and greenness index at all measurement dates than the control ones (
Table 8). Podsiadło and Jaroszewska [
56] claimed that the rise in both parameters indicated an improvement in plant nutritional status. Both in
Miscanthus sinensis and
Miscanthus ×
giganteus nitrogen index was the highest in plants grown in the presence of 15% of the biowaste. The leaves of
Miscanthus sinensis showed the most intense green coloration in plants growing in the substrate supplemented with 10% and 15% of shrimp biowaste at full bloom and at the end of the growing season. The control plants featured the lowest leaf greenness index of all variants. In
Miscanthus ×
giganteus leaf greenness increased along with growing dose of shrimp biowaste. Żurawik [
36] also claimed that
Freesia hybrida plants exposed to any dose of shrimp biowaste had significantly higher greenness index at the end of the growing season than the control plants. However, this was only true for
Miscanthus plants growing in the presence of 5% biowaste as compared with
Freesia hybrida exposed to 15% biowaste. Kulik et al. [
57] reported decreasing values of this parameter at consecutive measurements and the same tendency occurred in our study.