The Determination of Woody Biomass Resources and Their Energy Potential from Hazelnut Tree Cultivation

Abstract

The aim of this study was to estimate the shoot weight of four selected hazelnut cultivars and to see if the morphological characteristics of the cultivar and the age of the shoots affect their quality when used as fuel. This study shows that the cultivar ‘Olga’ generated the highest amounts of woody biomass (6507 t·ha⁻¹), while ‘Olbrzymi z Halle’ generated the lowest (3843 t·ha⁻¹). ‘Olbrzymi z Halle’ had the highest calorific values (HHVs) (18.08 MJ·t·ha⁻¹ for annual shoots and 18.03 MJ·kg⁻¹ for perennial shoots) and ‘Olga’ had the lowest calorific values (16.64 MJ·kg⁻¹ for annual shoots and 16.39 MJ·kg⁻¹ for perennial shoots). The age of the shoots had a minimal effect on the chemical and energy parameters. Emissions were the highest for ‘Olbrzymi z Halle’ (CO: 57.74 MJ·kg⁻¹ for perennial shoots, CO₂: 1414.05 MJ·kg⁻¹) and lowest for ‘Olga’ (CO: 50.57 MJ·kg⁻¹, CO₂: 1238.46 MJ·kg⁻¹). The cultivar ‘Olbrzymi z Halle’, which generated the least amount of biomass compared to the other cultivars, stands out for its high energy value due to its low moisture and ash contents and its high carbon and hydrogen contents, making it attractive for the purposes of biofuel production and supporting sustainable agriculture. The practical implications of the research findings include the selection of suitable varieties for biofuel production, the management of biomass moisture content, and the optimisation of combustion techniques to reduce emissions. The potential for using hazelnut shoots as a biofuel highlights the importance of sustainable agriculture and renewable energy production. The results provide valuable information that can support decisions regarding the cultivation and use of hazelnut shoots for biofuel production while minimising negative environmental impacts.

1. Introduction

Energy is one of the essential resources that determines economic, social, and political development, not only for countries but also for individual regions [1,2]. The cyclical nature of energy crises highlights a need to diversify energy sources, and achieving energy parity is difficult, particularly for countries relying heavily on traditional fossil fuels [3,4]. Biomass, as a renewable energy source (RES), can help bridge this gap while reducing greenhouse gas emissions. It is distinguished by its carbon neutrality, CO₂ sequestration capacity, energy storage capability, and higher energy density. In addition, it uses of residuals and has the potential for baseload generation, providing steady and consistent energy supply [5]. Due to their abundance and a lack of competition with the food industry, there is growing interest in the use of agricultural residues from different types of biomass [6]. This is particularly important as the solutions proposed by the European Commission at the UN COP25 climate summit in Madrid intend for the EU to become a zero-carbon economy by 2050, thus achieving climate neutrality [7,8,9]. Orchard residues offer an untapped opportunity for sustainable energy generation, and the agricultural sector is a good scenario for implementation due to the abundanceof the fruit and vegetable industry [10].

The common hazel is generally associated with another name, hazelnut;it is colloquially referred to as such, which refers to the fruit we all know—the nuts—which contain tasty and nutritious seeds. Also known as Corylus avellana, it is a perennial plant of temperate climates [11], tending to form a multi-stemmed, spreading shrub [12]. Hazel bushes can live from 70 to 80 to even 100 years, making them long-lived plants ideal for long-term use in a variety of applications, including biofuel production. Biomass production is therefore anongoing process, allowing for a constant supply for local industrial and energy chains. Of course, from an economic point of view, the most important use of hazelnuts is their industrial production. The main part of production focuses on harvesting the edible part of the nut, the kernel. The vegetative habit of the bush is often altered during orchard establishment and management. Depending on grower preferences, we can find shrubs with a single stem and an open Vshape, which facilitates mechanical harvesting and allows for greater sunlight penetration in the shrub rows [12]. In contrast, shrubs can be in the form of a multi-trunked shrub, which allows for the gradual renewal of the plant by eliminating old shoots and replacing them with new, woody offshoots [13]. Pruning hazel is one of the basic operations carried out during the cultivation of this shrub. Carried out once a year, pruning not only allows for the maintenanceof the proper appearance of the shrub and a regular and abundant yield [14] but also the thorough inspection and detectionof possible diseases or the presence of pests [13,15]. One of the typical responses of the plant to pruning is an increase in the rate of nut setting, which affects the productivity of the orchard.

There are three main types of pruning: formative, conservative, and rejuvenation pruning. The systematic pruning of shrubs produces large amounts of woody biomass consisting of shoots and branches of varying diameters. From one bush, a few to several kilograms of woody biomass can be obtained, which is an ecological, renewable, and versatile material. This makes hazelnut an excellent source of biomass with good heating properties, so it is obvious to use this raw material for energy production [16,17]. The extraction of branches for heating is neither a new nor an exploratory technology. Unfortunately, the most common practice still used in this process is to push the residues out of the inter-rows and dispose of them by burning, which allows the area to be quickly cleaned up before the new growing season. The problem is not the mass of the shoots obtained from cutting the orchard but their volume. The available technology allows baling, shredding, and using the residue to produce briquettes and pellets [11], which are easier to store and transport. It is estimated that 1.5 tonnes of woody biomass from orchard cutting can replace a tonne of coal. The amount of biomass harvested depends, among other things, on the age of the orchard, the variety of wood used, the number of plantings, environmental conditions [18,19], and the way the orchard is managed, i.e., whether the orchard is traditional or intensive [20].

The aim of the study was to estimate the shoot weight of four selected hazelnut varieties and to see whether the morphological characteristics of the variety and the age of the shoots affect their quality as fuel. The research included performing proximate and ultimate analyses, determining the heat of combustion and the calorific value. An assessment of emission factors, i.e., CO, CO₂, SO₂, NO_x, and dust, was also carried out to rate the environmental impact of potential bio-waste during combustion. The analysis of the flue gas composition was performed based on stoichiometric calculations.

2. Materials and Methods

This study aimed to estimate the amount of waste biomass obtained from the annual pruning of hazelnut bushes for 4 hazelnut cultivars, i.e., ‘Kataloński’, ‘Olbrzymi z Halle’, ‘Olga’, and ‘Webba Cenny’ and to check the influence of cultivar characteristics on shoot energy parameters.

Estimating biomass after pruning is a complicated task due to the different ways in which pruning is organised. In order to determine the amount of biomass harvested, it is necessary to refer to a specific number of plants; therefore, direct measurements in the field are necessary. Field research was conducted under temperate climate conditions, at a private horticultural farm located in the Sandomierska Upland (50°49′20.5″ N, 21°44′35.0″ E, Zawichost municipality, Świętokrzyskie province). The experimental material consisted of ungrafted hazel shrubs growing on their own roots of four cultivars: ‘Kataloński’, ‘Olbrzymi z Halle’, ‘Olga’, and ‘Webba Cenny’. The shrubs were planted in the spring of 2002 in a row cropping system, at a spacing of 6 × 2.5 m, i.e., 666 units per hectare, on loess soils (bonitation classes II and IIab). Plants were managed in a multi-row open vase form according to the natural bushy habit of the species.

Shoots for analysis were taken in February/March 2024 before the start of the hazel growing season. The study began with a random selection of shrubs (three trials for each cultivar), which were then subjected to a pruning treatment. The resulting shoot mass for each trial was segregated into annual and perennial shoots. Each sample was bundled and the biometric measurement of the harvested woody biomass for each cultivar was then carried out, allowing the mean value for the parameters studied to be determined. Immediately after the qualitative analysis, size tests were performed. The samples were weighed with an accuracy of 0.01 kg, and their weight was determined on a WLC RADWAG precision balance, which allowed the average weight of waste woody biomass to be estimated for each variety. From the material obtained, a representative sample was prepared for laboratory tests for each variety.

The analysis investigated the parameters of the biomass obtained per bush and per unit area of 1 ha.

The energy and emission parameters of the tested materials were also assessed. Detailed test procedures are shown in

Table 1. A summary of the methods and apparatuses used for the energy and carbon analysis of the raw materials studied.

	Parameter	Standard
Proximate Analysis	Higher Heating Value (HHV; MJ·kg−1)	EN-ISO 1928:2022; Equipment LECO AC 600 [21]
	Lower Heating Value (LHV; MJ·kg−1)
	Ash (A; %)	EN-ISO 18122-01; Equipment LECO TGA 701 [22]
	Volatile matter (V; %)	EN-ISO 18123-01; Equipment LECO TGA 701 [23]
	Moisture (M; %)	EN-ISO 18134-3; Equipment LECO TGA 701 [24]
	Fixed carbon (FC; %)	FC = 100-V-A-M [25]
Ultimate Analysis Emission factors calculated according to studies	Carbon (C;%)	EN-ISO 16948:2015-07, Equipment LECO CHNS 628 [26]
	Hydrogen (H;%)
	Nitrogen (N; %)
	Sulphur (S; %)	EN-ISO 16994:2016-10; Equipment LECO CHNS 628 [27]
	Oxygen (O; %)	O = 100-A-H-C-S-N [28]
Emission Factors Exhaust gas composition was calculated according to [29]	Carbon monoxide Emission factor (Ec) of chemically pure coal (CO; kg·Mg−1)	$CO={\displaystyle \frac{28}{12}}·E_c·\left(C\mathrm{CO}\right)$, CO—carbon monoxide emission factor (kg·kg−1), ${\displaystyle \frac{28}{12}}$—molar mass ratio of carbon monoxide and carbon, Ec—emission factor of chemically pure coal (kg∙kg−1), C/CO—part of the carbon emitted as CO (for biomass 0.06).
	Carbon dioxide emission factor (CO2; kg·Mg−1)	${CO}_2={\displaystyle \frac{44}{12}}·\left(E_c-{\displaystyle \frac{12}{28}}·CO-{\displaystyle \frac{12}{16}}·E_{{CH}_4}-{\displaystyle \frac{26.4}{31.4}}·E_{NMVOC}\right),$ CO2—carbon dioxide emission factor (kg∙kg−1), - molar mass ratio of carbon dioxide and pure coal, - molar mass ratio of carbon dioxide and carbon monoxide, - molar mass ratio of carbon and methane, ECH4—methane emission factor, ENMVOC—emission index of non-methane VOCs (for biomass 0.009).
	Sulphur dioxide emission factor (SO2; kg·Mg−1)	${SO}_2={\displaystyle \frac{2S}{100}}·\left(1-r\right),$ SO2–sulphur dioxide emission factor (kg∙kg−1), 2—molar mass ratio of SO2 and sulphur, S—sulphur content in fuel (%), r—coefficient determining the part of total sulphur retained in the ash.
	Emission factor was calculated from (NOX; kg·Mg−1)	${NO}_x={\displaystyle \frac{46}{14}}·E_c·N/C·\left(N_{{NO}_x}/N\right)$, NOx—NOx emission factor (kg∙kg−1),—molar mass ratio of nitrogen dioxide to nitrogen. The molar mass of nitrogen dioxide is considered due to the fact that nitrogen oxide in the air oxidises very soon to nitrogen dioxide, N/C—nitrogen-to-carbon ratio in biomass, NOx/N—part of nitrogen emitted as NOx (for biomass 0.122).
Exhaust gas composition [30,31]	Theoretical oxygen demand (VO2; Nm3·kg−1)	$V_{O_2}={\displaystyle \frac{22.41}{100}}·\left({\displaystyle \frac{C}{12}}+{\displaystyle \frac{H}{4}}+{\displaystyle \frac{S-O}{32}}\right)$, C-biomass carbon content (%), H-biomass hydrogen content (%), S-biomass sulphur content (%), O-biomass oxygen content).
	The stoichiometric volume of dry air required to burn 1 kg of biomass (VOa; Nm3·kg−)	$V_{O_a}={\displaystyle \frac{V_{O_2}}{0.21}},$ Since the oxygen content in the air is 21%, which participates in the combustion process in the boiler, the stoichiometric volume of dry air required to burn 1 kg of biomass
	Carbon dioxide content of the combustion products (VCO2; Nm3·kg−1)	$V_{{CO}_2}={\displaystyle \frac{22.41}{12}}$$· {\displaystyle \frac{C}{100}},$
	Content of sulphur dioxide (VSO2; Nm3·kg−1)	$V_{{SO}_2}={\displaystyle \frac{22.41}{32}}$$· {\displaystyle \frac{S}{100}}$,
	Water vapour content of the exhaust gas (VH2O; Nm3·kg−1)	$V_{H_{2}O}^H={\displaystyle \frac{22.41}{100}}·\left({\displaystyle \frac{H}{2}}+{\displaystyle \frac{M}{18}}\right)$, is the component of water vapour volume from the hydrogen combustion process $(V_{H_{2}O}^H$$; {\mathrm{Nm}}^3{\mathrm{H}}_2\mathrm{O}·\mathrm{kg}{-}^1\mathrm{fuel}) V_{H_{2}O}^a=1.61·x·V_{oa}$ and the volume of moisture contained in the combustion air $(V_{H_{2}O}^a$$; {\mathrm{Nm}}^3{\mathrm{H}}_2\mathrm{O}·\mathrm{kg}{-}^1\mathrm{fuel}) V_{H2O}$ $=V_{H2O}^H$ $+V_{H2O}^a$; M-fuel moisture content (%), -air absolute humidity (kg H2O·kg−1 dry air).
	The theoretical nitrogen content in the exhaust gas ($V_{N2}$; Nm3·kg−1)	$V_{N2}={\displaystyle \frac{22.41}{28}}·{\displaystyle \frac{N}{100}}+0.79·V_{oa}$, Considering that the nitrogen in the exhaust comes from the fuel composition and the combustion air, and the nitrogen content in the air is 79%.
	The total stoichiometric volume of dry exhaust gas ($V_{gu};$Nm3·kg−1)	$V_{gu}=V_{CO2}+V_{SO2}+V_{N2}$
	The total volume of exhaust gases ($V_{ga}$; Nm3·kg−1)	$V_{ga}=V_{gu}+V_{H2O}$ Assuming that biomass combustion is carried out under stoichiometric conditions, i.e., using the minimum amount of air required for combustion (λ = 1), a minimum exhaust gas volume will be obtained.

.

3. Results and Discussion

The study analysed the diversity of hazelnut varieties in terms of the yield of waste biomass in the form of shoots obtained during the annual bush pruning and their energy properties.

The multiple possible uses of hazelnut could lead to alternative productions that are not exclusively related to nutritional purposes. All this makes the by-products of hazelnut cultivation an interesting energy feedstock. This would avoid significant economic losses and reduce the cost of disposing of waste biomass. In addition, it would contribute to the sustainability of agroecosystems by reducing the amount of waste generated and greenhouse gases produced by the burning of residues, which often takes place directly in the fields [32].

Figure 1 shows the average amount of woody biomass generated by pruning the hazel orchard for selected varieties per unit area of 1 ha (t·ha⁻¹). Based on the measurements, it was shown that the shrubs of the cultivar ‘Olga’ generated the largest amount of woody biomass (6507.00 t·ha⁻¹), while ‘Olbrzymi z Halle’ generated the smallest amount (3843.00 t·ha⁻¹) among all the evaluated cultivars. The mass of woody biomass from ‘Kataloński’ and ‘Webba Cenny’ shrubs was similar and amounted to (4436.00 t·ha⁻¹ and 4289.00 t·ha⁻¹), respectively.

Table 2. Shoot quality analysis for four hazelnut cultivars for one bush.

Parameter	Average Number of Shoots (pcs.) for 1 Bush		Average Shoot Diameter (mm) at 50 cm Height on 1 Bush		Average Shoot Weight (kg·bush−1)
Age of shoots	one	many	one	many	one	many
‘Kataloński’	19.00 ± 7.94 A *	10.67 ± 1.15 A	12.91 ± 0.51 A	22.70 ± 3.03 A	1.78 ± 0.38 A	4.88 ± 1.38 A
‘Olbrzymi z Halle’	12.00 ± 1.73 A	8.67 ± 1.53 A	12.90 ± 1.68 A	20.77 ± 1.86 A	1.33 ± 0.66 A	4.44 ± 2.03 A
‘Olga’	10.33 ± 4.51 A	11.67 ± 1.15 A	12.20 ± 1.93 A	22.63 ± 8.06 A	1.33 ± 0.00 A	6.44 ± 2.52 A
‘Webba Cenny’	12.67 ± 0.57 A	10.00 ± 3.00 A	13.93 ± 2.98 A	20.90 ± 0.88A	1.78 ± 0.77 A	4.66 ± 0.66 A
p-value	0.8512	0.5632	0.2489	0.3697	0.5789	0.6328

* Significant difference Ameans that different letters in the column indicate significant differences at α = 0.05.

shows the results of the qualitative analysis of woody biomass for four hazelnut cultivars: ‘Kataloński’, ‘Olbrzymi z Halle’, ‘Olga’, and ‘WebbaCenny’. The analysis included parameters such as the number and diameter of shoots at a height of 50 cm and the average weight of one shoot of the bush divided into annual and perennial shoots for each of the categories mentioned.

The results indicate that the differences between varieties are not statistically significant. All analysed varieties have similar biometric properties in the context of waste biomass productivity, which means that varietal characteristics do not have a major impact on these parameters, and the choice of variety can be made on the basis of criteria other than the studied shoot biomass traits. In the average shoot number category, the values for the number of annual shoots range from 10.33 (‘Olga’) to 19.00 pcs. (‘Kataloński’). For perennial shoots, the numbers range from 8.67 (‘Olbrzymi z Halle’) to 11.67 units (‘Olga’). In the category of shoot diameter at 50 cm height, the highest values for annual shoots were recorded for the cultivar ‘Webba Cenny’ (13.93 mm) and the lowest for the cultivar ‘Olga’ (12.20 mm). Acampora et al. (2021) [33] demonstrated that the diameter of the pruned branches was 1.60 cm (range 1.44 to 22.00 cm). In the category of mean weight of uniplanted shoots, the highest values were obtained for the cultivar ‘Kataloński’ (1.78 t·ha⁻¹) and ‘Webba Cenny’ (1.78 t·ha⁻¹), and the lowest for the cultivar ‘Olga’ (1.33 t·ha⁻¹) and ‘Olbrzymi z Halle’ (1.33 t·ha⁻¹). In comparison, Di Giacinto et. al. [20] showed that the amount of biomass obtained from pruning is directly related to the age of the plants, their number per hectare, and the method of pruning. The average amount of biomass obtained in the study for a 15-year-old orchardin 2012 was1422 kg·ha⁻¹ and 3.80 kg/shrub, while in 2014, itwas 1354.00 kg·ha⁻¹ and 3.20 kg/shrub [20]. In contrast, the average amount of pruned biomass per plant obtained by Acampora et al. [33] was 4.17 kg fresh weight (ranging from 3.60 to 5.50 kg), corresponding to 1.67 t ha⁻¹ per year (0.90 t dry weight ha⁻¹ per year). In comparison, the apple tree, which dominates Polish orchards, produces about 3.50 Mg of woody biomass per ha from annual cutting [34,35].

The cluster analysis presented in the dendrogram (Figure 2) classifies hazelnut cultivars in terms of the amount of woody biomass generated. The dendrogram distinguishes two main clusters, which allows for an understanding of the differences in biomass productivity between varieties.

The division of varieties into two main clusters provides information on the potential use of different hazelnut varieties depending on specific production and energy needs. A dendrogram (Figure 2) illustrates the variation in woody biomass in selected areas. The varieties ‘Olbrzymi z Halle’ and ‘Olga’ show a higher amount of biomass generation, which can be beneficial in the context of energy applications. In contrast, ‘Webba Cenny’ and ‘Kataloński’ show a lower amount of biomass, which is important for waste management in intensively managed growing areas. With this information, it is possible to better plan and manage biomass resources in a way that maximises their energy potential and minimises waste costs.

Table 3. Proximate and ultimate analysis of woody biomass in relation to the variety used in hazel cultivation and the age of the shoots.

Parameter	Age of Shoots	Hazelnut Variety				p-Value
		‘Kataloński’	‘Olbrzymi z Halle’	‘Olga’	‘Webba Cenny’
LHV (MJ·kg−1)	One	15.43 ± 0.09 BCa *	16.85 ± 0.09 Aa	15.26 ± 0.05 Ca	15.61 ± 0.04 Ba	<0.0001
	Many	15.97 ± 0.09 BCa	17.44 ± 0.09 Aa	15.79 ± 0.05 Ca	16.16 ± 0.04 Ba	<0.0001
	p-value	0.2589	0.1369	0.7532	0.1598
HHV (MJ·kg−1)	One	16.79 ± 0.09 Ac	18.08 ± 0.09 Aa	16.64 ± 0.05 Ac	17.00 ± 0.04 Ab	<0.0001
	Many	16.83 ± 0.5 Ac	18.03 ± 0.04 Aa	16.39 ± 0.03 Ac	16.98 ± 0.06 Ab	<0.0004
	p-value	0.4893	0.7369	0.8361	0.1774
M (%)	One	16.76 ± 0.10 Ca	13.5 ± 0.06 Aa	18.04 ± 0.27 Da	17.48 ± 0.07 Ba	<0.0001
	Many	17.35 ± 0.10 Ca	13.97 ± 0.06 Aa	18.67 ± 0.28 Da	18.09 ± 0.07 Ba	<0.0001
	p-value	0.3190	0.1687	0.9280	0.1969
V (%)	One	64.99 ± 0.35 Ca	68.22 ± 0.34 Aa	64.93 ± 0.36 Ca	66.13 ± 0.39 Ba	<0.0001
	Many	67.26 ± 0.36 Ca	70.61 ± 0.35 Aa	67.20 ± 0.37 Ca	68.44 ± 0.40 Ba	<0.0001
	p-value	0.2770	0.1465	0.8059	0.1710
A (%)	One	2.40 ± 0.08 Aa	1.49 ± 0.05 BCa	1.77 ± 0.24 Ba	1.26 ± 0.06 Ca	<0.0001
	Many	2.48 ± 0.08 Aa	1.54 ± 0.051 BCa	1.83 ± 0.25 Ba	1.30 ± 0.06 Ca	<0.0001
	p-value	0.3075	0.1626	0.8946	0.1898
FC (%)	One	15.85 ± 0.41 Ba	16.78 ± 0.25 Aa	15.26 ± 0.41 Ba	15.12 ± 0.29 Ba	0.0014
	Many	16.40 ± 0.42 Ba	17.37 ± 0.26 Aa	15.79 ± 0.42 Ba	15.65 ± 0.30 Ba	0.0019
	p-value	0.2718	0.1437	0.7909	0.1678
C (%)	One	42.28 ± 0.5 Ba	45.29 ± 0.03 Aa	41.05 ± 0.22 Ca	42.76 ± 0.23 Ba	<0.0001
	Many	43.76 ± 0.52 Ba	46.88 ± 0.03 Aa	42.48 ± 0.23 Ca	44.26 ± 0.24 Ba	<0.0001
	p-value	0.3017	0.1596	0.8779	0.1862
H (%)	One	7.78 ± 0.15 Aa	7.1 ± 0.35 ABa	7.63 ± 0.22 ABa	7.09 ± 0.28 Ba	<0.0001
	Many	8.05 ± 0.15 Aa	7.35 ± 0.36 ABa	7.89 ± 0.23ABa	7.34 ± 0.29 Ba	<0.0001
	p-value	0.2822	0.1492	0.8210	0.1742
N (%)	One	0.95 ± 0.02 ABa	0.96 ± 0.01 Aa	0.87 ± 0.03 Ba	0.72 ± 0.05 Ca	<0.0001
	Many	0.98 ± 0.02 ABa	0.99 ± 0.01 Aa	0.90 ± 0.03 Ba	0.74 ± 0.05 Ca	<0.0001
	p-value	0.3132	0.1656	0.9113	0.1933
S (%)	One	0.05 ± 0 Aa	0.04 ± 0.01 Aa	0.05 ± 0 Aa	0.05 ± 0.02 Aa	0.5463
	Many	0.051 ± 0 Aa	0.04 ± 0.01 Aa	0.05 ± 0 Aa	0.05 ± 0.02 Aa	0.6874
	p-value	0.2900	0.1533	0.8436	0.1790
O (%)	One	46.54 ± 0.55 Ba	45.12 ± 0.34 Ca	48.62 ± 0.65 Aa	48.12 ± 0.13 Aa	<0.0001
	Many	48.17 ± 0.57 Ba	46.68 ± 0.35 Ca	50.32 ± 0.67 Aa	49.80 ± 0.13 Aa	<0.0001
	p-value	0.3219	0.1702	0.9364	0.1987
H/C	One	1.84 ± 0.04 Aa	1.57 ± 0.08 Ba	1.86 ± 0.04 Aa	1.66 ± 0.07 Ba	0.0009
	Many	1.90 ± 0.04 Aa	1.62 ± 0.08 Ba	1.92 ± 0.0414 Aa	1.71 ± 0.07 Ba	0.0007
	p-value	0.2977	0.1574	0.8662	0.1838
N/C	One	0.02 ± 0.001 Aa	0.02 ± 0.00 Aa	0.02 ± 0.001 Aa	0.02 ± 0.001 Ba	<0.0001
	Many	0.02 ± 0.001 Aa	0.021 ± 0.00 Aa	0.02 ± 0.001 Aa	0.02 ± 0.001 Ba	<0.0001
	p-value	0.3305	0.1748	0.9615	0.2040
O/C	One	0.83 ± 0.02 Ba	0.75 ± 0.01 Ca	0.88 ± 0.02 Aa	0.84 ± 0.01 Ba	<0.0001
	Many	0.85 ± 0.02 Ba	0.77 ± 0.01 Ca	0.92 ± 0.02 Aa	0.87 ± 0.01 Ba	<0.0001
	p-value	0.2680	0.1417	0.7796	0.1654

* Significant difference a, b and c means that different letters in the column, and A, B, and C means that different letters in the row indicate significant differences at α = 0.05.

shows the results of a comparative technical and elemental analysis of woody biomass according to the variety used in hazel cultivation and the age of the shoots. The parameters analysed include the lower heat of combustion (LHV), higher heat of combustion (HHV), moisture content (M), volatile compound content (V), ash content (A), fixed carbon content (FC), and elemental composition of carbon (C), hydrogen (H), nitrogen (N), sulphur (S), and oxygen (O). In addition, the analysis includes ratios, i.e., hydrogen to carbon (H/C), nitrogen to carbon (N/C), and oxygen to carbon (O/C).

The results of the proximateand ultimate analysis of shoot biomass of the four hazel cultivars showed no statistically significant differences between shoot ages. These differences are small, indicating a relatively similar level of content of the studied parameters in the biomass of the cultivars, irrespective of the age of the shoots.In contrast, significant relationships between the studied parameters were observed for the effect of varietal traits, with the exception of sulphur content.

For annual shoots, LHV values range from 15.26 MJ·kg⁻¹ for ‘Olga’ to 16.85 MJ·kg⁻¹ for ‘Olbrzymi z Halle’, while for perennial shoots the values range from 15.79 to 17.44 MJ·kg⁻¹ for the same cultivars. The results show small differences in the biomass energy potential between the cultivars, which are 1.59 MJ·kg⁻¹ for annual shoots and 1.65 MJ·kg⁻¹ for perennial shoots, respectively. Their low level is indicative of the relatively similar biomass energy potential of the cultivars, irrespective of the age of the shoots.

In contrast, for annual and perennial shoots, the highest HHV was recorded for ‘Olbrzymi z Halle’ (18.08 MJ·kg⁻¹, 18.03 MJ·kg⁻¹) and the lowest for the cultivar ‘Olga’ (16.64 MJ·kg⁻¹, 16.39 MJ·kg⁻¹). The high HHV for ‘Olbrzymi z Halle’ suggests a higher energy yield, making this variety more attractive for biomass energy production. Lower HHVs for ‘Olga’ may imply lower energy suitability, but may be beneficial in other contexts, i.e., waste management. In comparison, Stolarski et. al. [36] showed higher calorific values for lignocellulosic biomass samples of fruit trees, i.e., peach tree HHV 20.10 MJ·kg⁻¹, LHV 18.80 MJ·kg⁻¹; pear HHV 19.20 MJ·kg⁻¹, LHV 17.80 MJ·kg⁻¹; apple HHV 19.20 MJ·kg⁻¹, LHV 17.90 MJ·kg⁻¹; hazelnut HHV 19.60 MJ·kg⁻¹, LHV 18.20 MJ·kg⁻¹; and plum HHV 19.60 MJ·kg⁻¹, LHV 18.20 MJ·kg⁻¹. The difference between the results of the present study and those of Stolarski et al. [36] for hazelnut was for LHV 1.35 MJ·kg⁻¹and for HHV 1.52 MJ·kg⁻¹. In contrast, Zambon [37] reported an HHV value of 19.02 MJ·kg⁻¹ and an LHV value of 16.71 MJ·kg⁻¹ for pruned hazelnut. In contrast, Cavalaglio et al. [10] obtained values of 16.3 MJ·kg⁻¹ and 17.56 MJ·kg⁻¹ for LHV and HHV, respectively. Comparing the energy value with other types of biomass from hazelnut production and processing, it can be shown that the tested shoots have a lower LHV in relation to hazelnut shells [38] and hazelnut tree pellets [33] (only higher values of 17.44 MJ·kg⁻¹ were obtained for perennial shoots of the cultivar ‘Olbrzymi z Halle’) and a lower HHV in relation to hazelnut tree leaves, hazelnut shells and hazelnut, and alder chips [39].

The moisture content, a key parameter influencing combustion quality, shows little difference, with evidence of relatively similar biomass moisture levels for both cultivars, regardless of the shoot age. For annual shoots, the moisture content (M) values range from 13.5% for ‘Olbrzymi z Halle’ to 18.04% for ‘Olga’. For perennial shoots, on the other hand, the values range from 13.97% for ‘Olbrzymi z Halle’ to 18.67% for ‘Olga’. The results show differences in the biomass moisture content between cultivars, which are 4.54% for annual shoots and 4.70% for perennial shoots, respectively. Cavalaglio et al. [10] obtained much lower values for this parameter of 10.39% in their study. The differences between the results of the present study and those of Cavalaglio et al. [10] depending on shoot age are for the highest value 7.65% for annual shoots and 8.28% for perennial shoots. And for the lowest value, the differences are 3.11% for annual shoots and 3.58% for perennial shoots. Compared with other types of biomass from hazelnut cultivation like hazelnut husk, Mladenovic et al. [38] obtained12.84% for this parameter.

In the case of volatile compounds (V) for annual shoots, their values range from 64.93% for the cultivar ‘Olga’ to 68.22% for the cultivar ‘Olbrzymi z Halle’. For perennial shoots, the values range from 67.20% to 70.61% for the same cultivars. The results show differences in the volatile matter content of biomass between the cultivars, which are 3.29% for annual shoots and 3.41% for perennial shoots, respectively. However, these differences are small, indicating relatively similar levels of biomass volatile matter content of both cultivars, regardless of the shoot age. Cavalaglio et al. [10] obtained higher results of 77.4% for the parameter studied.

For annual shoots, the ash content (A) varies from 1.26% for ‘Webba Cenny’ to 2.40% for ‘Kataloński’. As for the perennial shoots, the values range from 1.30 to 2.48% for the same varieties. The results show differences in ash content in the biomass between varieties, which are 1.14% for annual shoots and 1.18% for perennial shoots, respectively. These differences are small, indicating a relatively similar level of ash content in the biomass of the cultivars, regardless of the shoot age. Stolarski et al. [36] report the following values for ash content regardless of the shoot age and cultivar for peach tree 2.0%, pear tree 3.8%, apple tree 1.9%, hazelnut 2.5%, and plum tree 1.5%. In contrast, Di Giacinto [20] obtained much higher ash values for the hazelnut tree in his study, which amounted to 6.57%, while Cavalaglio et al. [10] obtained 2.59%.

The fixed carbon (FC) values for annual shoots vary from 15.12% for the cultivar ‘Webba Cenny’ to 16.78% for the cultivar ‘Olbrzymi z Halle’. For perennial shoots, the values vary from 15.65% for the cultivar ‘Webba Cenny’ to 17.37% for the cultivar ‘Olbrzymi z Halle’. The results indicate that the solid carbon content of the biomass is quite similar between the cultivars for both annual and perennial shoots. The small differences of 1.66% and 1.72% suggest that the age of the shoots does not significantly affect the solid carbon content of the biomass of both cultivars.

The carbon (C) content for annual shoots ranges from 41.05% for ‘Olga’ to 45.29% for ‘Olbrzymi z Halle’. For perennial shoots, the values range from 42.48% for ‘Olga’ to 46.88% for ‘Olbrzymi z Halle’. The small differences of 4.24% and 4.40%, respectively, suggest that shoot age has a minimal effect on the biomass carbon content of both cultivars.

For annual shoots, the hydrogen (H) content ranges from 7.09% for ‘Webba Cenny’ to 7.78% for ‘Kataloński’. For perennial shoots, the values range from 7.34% for ‘Webba Cenny’ to 8.05% for ‘Kataloński’. The differences of 0.69% and 0.71%, respectively, suggest that the age of the shoots does not significantly affect the hydrogen content of the biomass of both cultivars.

For annual shoots, the nitrogen (N) content ranges from 0.72% for ‘Webba Cenny’ to 0.96% for ‘Olbrzymi z Halle’. For perennial shoots, the values range from 0.74% for ‘Webba Cenny’ to 0.99% for ‘Olbrzymi z Halle’. These results show that the nitrogen content of the biomass is similar between varieties for both annual and perennial shoots. Differences of 0.24% and 0.25%, respectively, suggest that shoot age has a minimal effect on the biomass nitrogen content of both cultivars.

Stolarski et al. [36] reported the following higher percentages: peach C—51.10%, H—6.30%, N—0.90%; pear C—49.00%, H—6.30%, N—0.80%; apple C—48.60%, H—6.20%, N—0.50%; hazel C—49.80%, H—6.40%, N—0.80%; plum C—49.50%, H—6.30%, and N—0.60%. On the other hand, Bilandzija (2012) [40] reported C—46.46%, H—6.57%, and N—0.78%, while Di Giacinto [20] obtained similar values of C—48.70%, H—6.17% and N—1.09%.Cavalaglio et al. [10] showed the following values for hazelnut: C—43.80%, H—6.1%, and N-0–16.00%.

The sulphur (S) content for annual shoots varies from 0.04% for ‘Olbrzymi z Halle’ to 0.05% for ‘Kataloński’, ‘Olga’, and ‘Webba Cenny’ varieties. And for perennial shoots, the values are 0.04% for the cultivars ‘Olbrzymi z Halle’ and ‘Kataloński’ and 0.05% for the cultivars ‘Olga’ and ‘Webba Cenny’. These results show that the sulphur content of the biomass is almost identical between the varieties regardless of the age of the shoots. Differences of 0.01% suggest that shoot age does not significantly affect the biomass sulphur content of both cultivars.

In contrast, the oxygen (O) content for annual shoots ranges from 45.12% for ‘Olbrzymi z Halle’ to 48.62% for ‘Olga’. For perennial shoots, the values range from 46.68% for the cultivar ‘Olbrzymi z Halle’ to 50.32% for the cultivar ‘Olga’. These results show that the oxygen content of the biomass varies between cultivars within a similar range for both annual and perennial shoots. The differences of 3.50% and 3.64%, respectively, suggest that shoot age has a minimal effect on the oxygen content of the biomass of both cultivars.

The hydrogen-to-carbon (H/C) ratio for annual shoots ranges from 1.57% for ‘Olbrzymi z Halle’ to 1.86% for ‘Olga’. For perennial shoots, the values range from 1.62% for the cultivar ‘Olbrzymi z Halle’ to 1.92% for the cultivar ‘Olga’. These results show that the ratio of hydrogen to carbon in the biomass is similar between cultivars, regardless of the age of the shoots. Differences of 0.29 and 0.30%, respectively, suggest that shoot age has a minimal effect on the hydrogen/carbon ratio in the biomass of both cultivars.

For the nitrogen-to-carbon (N/C) ratio in the biomass, the results show that it is almost identical (with the single exception of ‘Olbrzymi z Halle’ 0.021%) between cultivars regardless of the shoot age. The age of the shoots has a negligible effect on the nitrogen-to-carbon ratio in the biomass.

Figure 3 shows the results of the principal component correlation analysis carried out on hazelnut shoots, irrespective of the age of the shoots and hazel variety indicate the existence of four main clusters of physico-chemical parameters. Each of these clusters reflects specific patterns of correlations between the parameters studied, allowing a better understanding of the properties of the shoots.

The first cluster includes parameters related to the energy potential of the shoots, such as the LHV (lower heating value), HHV (higher heating value), carbon content (C), and volatility (V). The strong correlation between LHV and HHV suggests that higher carbon content and volatility lead to higher calorific value, which is crucial for assessing biomass quality as a fuel. The second cluster focuses on parameters, i.e., the moisture content (M), sulphur content (S), oxygen (O), and oxygen-to-carbon ratio (O/C). High moisture content can reduce combustion efficiency, while the presence of sulphur is important from an emissions point of view. Oxygen content and O/C ratio affect oxidation and reactivity processes during combustion, which can be important for combustion and emissions control. The third cluster includes parameters related to hydrogen content, i.e., hydrogen/carbon ratio (H/C), hydrogen content (H), and ash content (A). The hydrogen content influences the calorific value of the shoots, while the ash content is important for assessing the environmental impact and the combustion equipment, due to the possible formation of ash residues. The fourth cluster focuses on parameters, i.e., thenitrogen-to-carbon ratio (N/C), nitrogen content (N), and fixed carbon content (FC). These parameters are key to understanding combustion characteristics, especially in the context of potential nitrogen oxides (NOx) emissions. The fixed carbon content indicates the potential of the biomass for sustained combustion and its energy efficiency. The analysis identifies the key characteristics of hazelnut shoots that have a significant impact on their energy value and potential environmental impact. Understanding these correlations enables better use of biomass in the context of energy production and minimisation of negative environmental impacts.

Table 4. Emission parameters for woody biomass depending on the variety used in hazel cultivation and the age of the shoots.

Parameter	Age of Shoots	Hazelnut Variety				p-Value
		‘Kataloński’	‘Olbrzymi z Halle’	‘Olga’	‘Webba Cenny’
CO (kg·Mg−1)	One	52.09 ± 0.62 Ba *	55.79 ± 0.04 Aa	50.57 ± 0.27 Ca	52.67 ± 0.29 Ba	<0.0001
	Many	53.91 ± 0.64 Ba	57.74 ± 0.04 Aa	52.34 ± 0.28 Ca	54.51 ± 0.30 Ba	<0.0001
	p-value	0.3359	0.4598	0.3315	0.4897
CO2 (kg·Mg−1)	One	1275.51 ± 15.15 Ba	1366.23 ± 0.97 Aa	1238.46 ± 6.55 Ca	1289.89 ± 7.08 Ba	<0.0001
	Many	1320.15 ± 15.68 Ba	1414.05 ± 1.00 Aa	1281.81 ± 6.78 Ca	1335.04 ± 7.33 Ba	<0.0001
	p-value	0.3859	0.5282	0.3808	0.5626
Nox (kg·Mg−1)	One	3.37 ± 0.06 ABa	3.4 ± 0.05 Aa	3.08 ± 0.1 Ba	2.54 ± 0.19 Ca	<0.0001
	Many	3.49 ± 0.06 ABa	3.52 ± 0.05 Aa	3.19 ± 0.10 Ba	2.63 ± 0.19 Ca	<0.0001
	p-value	0.4139	0.5665	0.4084	0.6034
SO2 (kg·Mg−1)	One	0.09 ± 0.01 Aa	0.08 ± 0.01 Aa	0.11 ± 0.01 Aa	0.11 ± 0.04 Aa	0.5463
	Many	0.09 ± 0.01 Aa	0.09 ± 0.01 Aa	0.11 ± 0.01 Aa	0.11 ± 0.04 Aa	0.5578
	p-value	0.3728	0.5104	0.3680	0.5436
Dust (kg·Mg−1)	One	3.03 ± 0.1 Aa	1.88 ± 0.07 BCa	2.24 ± 0.3 Ba	1.6 ± 0.08 Ca	<0.0001
	Many	3.14 ± 0.10 Aa	1.95 ± 0.07 BCa	2.32 ± 0.31 Ba	1.66 ± 0.08 Ca	<0.0001
	p-value	0.3477	0.4759	0.3431	0.5068

* Significant difference a means that different letters in the column, and A, B, C means that different letters in the row indicate significant differences at α = 0.05.

shows the results of the emissions analyses for woody biomass for the four hazel cultivars and as a function of the shoot age (annual vs. perennial). Parameters analysed include carbon monoxide (CO), carbon dioxide (CO₂), oxides of nitrogen (NO_x), sulphur dioxide (SO₂), and dust emissions expressed in kg·Mg⁻¹.

The analyses of pollutant emission parameters for woody biomass of four hazel cultivars showed no statistically significant differences between annual and perennial shoots for the parameters analysed. This means that pollutant emissions are relatively stable as shoots age, regardless of cultivar. In contrast, significant relationships between the parameters studied were observed for the effect of cultivar morphological characteristics, with the exception of sulphur dioxide emissions (SO₂). These differences indicate a significant influence of cultivar on biomass combustion processes, which can affect emissions such as CO, CO₂, NO_x, and dust.

For annual shoots, carbon monoxide (CO) emissions range from 50.57 kg·Mg⁻¹ for ‘Olga’ to 55.79 kg·Mg⁻¹ for ‘Olbrzymi z Halle’. Similar results were obtained for perennial shoots, where values range from 52.34 kg·Mg⁻¹ for ‘Olga’ to 57.74 kg·Mg⁻¹ for ‘Olbrzymi z Halle’. The largest variations between cultivars were observed in the annual shoot category (5.22 kg·Mg⁻¹) and between shoot ages for ‘Olga’ (1.77 kg·Mg⁻¹).

Carbon dioxide emissions (CO₂) for annual shoots range from 1238.46 kg·Mg⁻¹ for cultivar ‘Olga’ to 1366.23 kg·Mg⁻¹ for ‘Olbrzymi z Halle’. For perennial shoots, the values range from 1281.81 kg·Mg⁻¹ for ‘Olga’ to 1414.05 kg·Mg⁻¹ for ‘Olbrzymi z Halle’. The largest variations between cultivars occurred in the annual shoot category (127.77 kg·Mg⁻¹) and between the annual and perennial categories for ‘Olga’ (47.82 kg·Mg⁻¹).

The analysis of nitrogen oxides (NO_x) shows that for annual shoots the emissions range from 2.54 kg·Mg⁻¹ for ‘Webb Cenny’ to 3.37 kg·Mg⁻¹ for ‘Kataloński’. For perennial shoots, the values range from 2.23 kg·Mg⁻¹ for ‘Webba Cenny’ to 3.49 kg·Mg⁻¹ for ‘Kataloński’. The greatest variation between varieties was observed in the annual shoot category (1.27 kg·Mg⁻¹), and between the annual and perennial categories for ‘Webba Cenny’ (0.13 kg·Mg⁻¹).

For sulphur dioxide (V_SO2), on the other hand, the emission for annual shoots ranges from 0.08 kg-Mg⁻¹ for the cultivar ‘Olbrzymi z Halle’ to 0.11 kg·Mg⁻¹ for the cultivars ‘Olga’ and ‘Webba Cenny’. In the case of perennial shoots, the values range from 0.09 kg·Mg⁻¹ for the cultivars ‘Kataloński’ and ‘Olbrzymi z Halle’ to 0.11 kg·Mg⁻¹ for the cultivars ‘Olga’ and ‘Webba Cenny’. There is little variation between varieties and shoot age.

In contrast, dust emissions for annual shoots range from 1.60 kg·Mg⁻¹ for ‘Webba Cenny’ to 3.03 kg·Mg⁻¹ for ‘Kataloński’. A similar relationship was observed for perennial shoots where the values range from 1.66 kg·Mg⁻¹ for ‘Webba Cenny’ to 3.14 kg·Mg⁻¹ for ‘Kataloński’. The largest variations between varieties occurred in the annual shoot category (1.43 kg·Mg⁻¹) and between the annual and perennial categories for ‘Kataloński’ (0.11 kg·Mg⁻¹).

The differences in emissions are more pronounced between cultivars than between shoot ages. The largest variations between varieties occurred for carbon dioxide emissions (CO₂) in the annual shoot category, while the smallest differences were recorded for sulphur dioxide emissions (SO₂) in the same category. Thecomparisons between age categories showed that the largest differences were in dust emissions for the ‘Kataloński’ cultivar and the smallest for sulphur dioxide (SO₂) for the same cultivar.

Figure 4 shows two dendrograms that analyse the four hazelnut varieties in terms of their calorific value, HHV (Figure 4a,) and proximal and terminal analysis parameters (Figure 4b).

By comparing the two dendrograms (Figure 4a,b), it can be seen that the chemical composition of the biomass has a key influence on its calorific value. The varieties with higher carbon and hydrogen content and lower moisture and ash content (‘Olbrzymi z Halle’ and ‘Olga’) have a higher energy value. The varieties with a higher moisture and ash content (‘Webba Cenny’ and ‘Kataloński’) have a lower energy value. These relationships should be taken into account when selecting varieties for woody biomass energy production. In addition, understanding these relationships has practical implications for hazelnut crop management. The cultivars with a higher energy value may be more profitable for biomass production for energy purposes, which may influence farmers’ decisions on which varieties to grow.

The analytical results presented in

Table 5. Composition of woody biomass exhaust depending on the variety used in hazel cultivation and the age of the shoots.

Parameter	Age of Shoots	Hazelnut Variety				p-Value
		‘Kataloński’	‘Olbrzymi z Halle’	‘Olga’	‘Webba Cenny’
VoO2 (Nm3·kg−1)	One	0.89 ± 0.02 Aba *	0.93 ± 0.02 Aa	0.85 ± 0.02 Ba	0.86 ± 0.01 Ba	0.0033
	Many	0.93 ± 0.02 ABa	0.96 ± 0.02 Aa	0.88 ± 0.02 Ba	0.89 ± 0.01 Ba	0.0029
	p-value	0.5239	0.5189	0.4996	0.6123
Voa (Nm3·kg−1)	One	4.28 ± 0.07 ABa	4.42 ± 0.10 Aa	4.07 ± 0.09 Ba	4.09 ± 0.06 Ba	0.0033
	Many	4.43 ± 0.08 ABa	4.57 ± 0.11 Aa	4.21 ± 0.10 Ba	4.23 ± 0.06 Ba	0.0029
	p-value	0.5606	0.5552	0.5346	0.6552
VCO2 (Nm3·kg−1)	One	0.79 ± 0.01 Ba	0.85 ± 0.00 Aa	0.77 ± 0.00 Ca	0.79 ± 0.00 Ba	<0.0001
	Many	0.82 ± 0.01 Ba	0.87 ± 0.00 Aa	0.79 ± 0.00 Ca	0.83 ± 0.00 Ba	<0.0001
	p-value	0.5815	0.5760	0.5546	0.6797
VSO2 (Nm3·kg−1)	One	0.0003 ± 0.00 Aa	0.0003 ± 0.00 Aa	0.0004 ± 0.00 Aa	0.0004 ± 0.00 Aa	0.5463
	Many	0.0003 ± 0.00 Aa	0.0003 ± 0.00 Aa	0.0004 ± 0.00Aa	0.0004 ± 0.00 Aa	0.5498
	p-value	0.6503	0.6163	0.5934	0.7272
VH2O (Nm3·kg−1)	One	1.08 ± 0.02 Aa	0.96 ± 0.04 Ba	1.08 ± 0.02 Aa	1.01 ± 0.03 ABa	0.0024
	Many	1.12 ± 0.01 Aa	0.99 ± 0.04 Ba	1.12 ± 0.03 Aa	1.05 ± 0.03 ABa	0.0029
	p-value	0.6455	0.6393	0.6156	0.7544
VN2 (Nm3·kg−1)	One	4.15 ± 0.05 Aa	4.26 ± 0.08 Aa	3.91 ± 0.09 Ba	3.81 ± 0.04 Ba	<0.0001
	Many	4.29 ± 0.05 Aa	4.41 ± 0.08 Aa	4.05 ± 0.09 Ba	3.94 ± 0.04 Ba	<0.0001
	p-value	0.8523	0.8111	0.7398	0.6379
Vgu (Nm3·kg−1)	One	4.94 ± 0.06 Aa	5.11 ± 0.08 Aa	4.68 ± 0.09 Ba	4.61 ± 0.03 Ba	<0.0001
	Many	5.10 ± 0.06 Aa	5.29 ± 0.08 Aa	4.84 ± 0.09 Ba	4.77 ± 0.04 Ba	<0.0001
	p-value	0.6077	0.6019	0.5795	0.7103
Vga (Nm3·kg−1)	One	6.71 ± 0.08 Aa	6.78 ± 0.13 Aa	6.41 ± 0.13 Ba	6.28 ± 0.07 Ba	0.0013
	Many	6.94 ± 0.08 Aa	7.02 ± 0.14 Aa	6.64 ± 0.14 Ba	6.45 ± 0.07 Ba	0.0019
	p-value	0.7050	0.6681	0.6433	0.7884

* Significant difference a, b means that different letters in the column, and A, B, C means that different letters in the row indicate significant differences at α = 0.05.

show the composition of woody biomass exhaust depending on the variety used in hazelnut cultivation and the age of the shoots. The analysis includes eight key parameters related to the combustion process: V_O2, V_oa, V_CO2, V_SO2, V_H2O, V_N2, V_gu, and V_g, expressed in normal cubic metres per kilogram (Nm³·kg⁻¹). Statistically significant differences were shown in most parameters between cultivars and shoot age, with the exception of V_SO2 emissions, which showed no significant differences.

For annual shoots, the V_O2 emission ranges from 0.85 Nm³·kg⁻¹ for the cultivar ‘Olga’ to 0.93 Nm³·kg⁻¹ for ‘Olbrzymi z Halle’. Similar results were obtained for perennial shoots, where values range from 0.88 Nm³·kg⁻¹ to 0.96 Nm³·kg⁻¹ for the same cultivars. The largest variations between cultivars were observed in the annual shoot category (0.08 Nm³·kg⁻¹) and between shoot ages for the cultivar ‘Olbrzymi z Halle’ (0.03 Nm³·kg⁻¹).

For V_Oa, emissions for annual shoots range from 4.07 Nm³·kg⁻¹ for cultivar ‘Olga’ to 4.42 Nm³·kg⁻¹ for ‘Olbrzymi z Halle’. For perennial shoots, the values range from 4.21 Nm³·kg⁻¹ to 4.57 Nm³·kg⁻¹ for the same varieties. The largest variations between cultivars occurred in the annual shoot category (0.35 Nm³·kg⁻¹) and between the annual and perennial categories for ‘Olbrzymi z Halle’ (0.15 Nm³·kg⁻¹).

The V_CO2 analysis shows that for annual shoots, the emissions range from 0.77 Nm³·kg⁻¹ for ‘Olga’ to 0.85 Nm³·kg⁻¹ for ‘Olbrzymi z Halle’. For perennial shoots, the values range from 0.79 Nm³·kg⁻¹ for ‘Olga’ to 0.82 Nm³·kg⁻¹ for ‘Kataloński’. The largest variation between cultivars was observed in the annual shoot category (0.08 Nm³·kg⁻¹), and between the annual and perennial categories for ‘Kataloński’ (Nm³·kg⁻¹).

For sulphur dioxide (V_SO2), the emissions for annual and perennial shoots show the same relationships, where the values are 0.0003 Nm³·kg⁻¹ for the cultivars ‘Kataloński’ and ‘Olbrzymi z Halle’ and 0.0004 Nm³·kg⁻¹ for ‘Olga’ and ‘Webba Cenny’. The fluctuations between cultivars and shoot age are small and not statistically significant.

V_H2O emissions for annual shoots range from 0.96 Nm³·kg⁻¹ for the cultivar ‘Olbrzymi z Halle’ to 1.08 Nm³·kg⁻¹ for ‘Kataloński’ and ‘Olga’. For perennial shoots, the values range from 0.99 Nm³·kg⁻¹ for ‘Olbrzymi z Halle’ to 1.12 Nm³·kg⁻¹ for ‘Kataloński’ and ‘Olga’. The largest variation between cultivars occurred in the annual shoot category (0.12 Nm³·kg⁻¹) and between the annual and perennial categories for the cultivar ‘Kataloński’ (0.04 Nm³·kg⁻¹).

The V_N2 emissions for annual shoots range from 3.81 Nm³·kg⁻¹ for the cultivar ‘WebbaCenny’ to 4.26 Nm³·kg⁻¹ for ‘Olbrzymi z Halle’. For perennial shoots, the values range from 3.94 Nm³·kg⁻¹ for the cultivar ‘Webba Cenny’ to 4.41 Nm³·kg⁻¹ for ‘Olbrzymi z Halle’. The largest fluctuations between varieties occurred in the annual shoot category (0.45 Nm³·kg⁻¹) and between the annual and perennial categories for ‘Olbrzymi z Halle’ (0.15 Nm³·kg⁻¹).

V_gu emissions for annual shoots range from 4.61 Nm³·kg⁻¹ for ‘Webba Cenny’ to 5.11 Nm³·kg⁻¹ for ‘Olbrzymi z Halle’. For perennial shoots, the values range from 4.77 Nm³·kg⁻¹ for the cultivar ‘Webba Cenny’ to 5.29 Nm³·kg⁻¹ for ‘Olbrzymi z Halle’. The largest variations between varieties occurred in the annual shoot category (0.50 Nm³·kg⁻¹), and between the annual and perennial categories for ‘Olbrzymi z Halle’ (0.18 Nm³·kg⁻¹).

The V_ga emission for annual shoots ranges from 6.28 Nm³·kg⁻¹ for the cultivar ‘Webba Cenny’ to 6.78 Nm³·kg⁻¹ for ‘Olbrzymi z Halle’. For perennial shoots, the values range from 6.45 Nm³·kg⁻¹ for the cultivar ‘Webba Cenny’ to 7.02 Nm³·kg⁻¹ for ‘Olbrzymi z Halle’. The largest variation between varieties occurred in the annual shoot category (0.50 Nm³·kg⁻¹) and between the annual and perennial categories for ‘Olbrzymi z Halle’ (0.24 Nm³·kg⁻¹).

The differences in emissions are more pronounced between varieties than between shoot ages (annual vs. perennial). The largest variations between varieties occurred for V_O2 emissions in the one-year shoot category, while the smallest differences were recorded for VSO₂ emissions in the same category. On the other hand, comparisons between age categories showed that the largest differences were in the V_O2 emission for the cultivar ‘Olbrzymi z Halle’ and the smallest for the V_SO2 emission for all cultivars. Statistically significant differences were shown in most parameters between cultivars and shoot age, with the exception of V_SO2 emission, which showed no significant differences.

In summary, hazelnut is an excellent example of a functional food due to its taste and nutritional and health-promoting qualities, providing a valuable raw material not only in the kitchen. Less well known, but equally important, is the use of the waste biomass generated during its production. Of course, from an economic point of view, the most important use of hazelnuts is the industrial production of hazelnuts. The main part of production focuses on obtaining the edible part of the nut, the kernel. Nevertheless, the uncertainty of production, due to climatic conditions or disease, can be an excellent incentive for crop diversification. One area of diversification is the use of the waste material generated during nut production—not only the shoots, but also the leaves, woody skins, or pericarp pith—to produce biofuels. This type of practice is already in use in some regions, where agricultural waste is processed through processes such as pyrolysis or fermentation, transforming it into bioenergy. Such a model not only helps producers better compensate for economic losses, but also contributes to sustainable development, more efficient waste management and the development of local entrepreneurship. Importantly, this model does not compromise the safety of food production, as it uses by-products that would otherwise be waste. Thus, the development of alternative uses for by-products, including as biofuels, is not only possible but desirable. Of course, there may be some challenges in implementing such solutions, such as the cost of the technology and the need for further research, but the environmental and economic benefits outweigh the potential difficulties [41,42,43].

4. Conclusions

The results showed that the cultivar ‘Olga’ generated the highest amounts of woody biomass (6507.00 t·ha⁻¹), while the cultivar ‘Olbrzymi z Halle’ generated the lowest amount (3843.00 t·ha⁻¹). The cultivars ‘Kataloński’ and ‘Webba Cenny’ had similar results of 4436.00 t·ha⁻¹ and 4289.00 t·ha⁻¹, respectively. The highest heating values (HHV) were recorded for ‘Olbrzymi z Halle’ (18.08 MJ·kg⁻¹ for annual shoots and 18.03 MJ·kg⁻¹ for perennial shoots), while the lowest calorific values were recorded for ‘Olga’ (16.64 MJ·kg⁻¹ for annual shoots and 16.39 MJ·kg⁻¹ for perennial shoots).

The age of the shoots had minimal effect on the chemical and energy parameters, meaning that both younger and older shoots could be effectively used for energy production. The study showed significant correlations between the tested cultivars in terms of emissions. The highest CO emissions were recorded for the cultivar ‘Olbrzymi z Halle’ (57.74 MJ·kg⁻¹ for perennial shoots) and the lowest for ‘Olga’ (50.57 MJ·kg⁻¹ for annual shoots). CO₂ emissions were highest for ‘Olbrzymi z Halle’ (1414.05 MJ·kg⁻¹ for perennial shoots) and lowest for ‘Olga’ (1238.46 MJ·kg⁻¹ for one-year shoots). NO_x emissions were highest for ‘Kataloński’ (3.52 MJ·kg⁻¹ for perennial shoots) and lowest for ‘Webba Cenny’ (2.54 MJ·kg⁻¹ for one-year shoots).

The hazelnut variety ‘Olbrzymi z Halle’ is distinguished by its highest calorific values, which makes it attractive for biofuel production. Although it does not generate the greatest amount of woody biomass (t·ha⁻¹), its low moisture and ash content increases its energy value and combustion efficiency. The high carbon and hydrogen content of ‘Olbrzymi z Halle’ biomass translates into a higher energy value, and its moderate emissions make it more environmentally friendly. This makes ‘Olbrzymi z Halle’ recommended for biomass energy production, supporting sustainable agriculture and renewable energy production.

The practical implications of the research results include the selection of suitable varieties for biofuel production, management of biomass moisture content, and optimisation of combustion techniques to reduce emissions. The research results can support decisions on the cultivation and use of hazelnut in biofuel production. The high HHV for ‘Olbrzymi z Halle’ suggests a higher energy yield, making this variety attractive for biomass energy production. The varieties with higher carbon and hydrogen content and lower moisture and ash content have a higher energy value. The potential to use hazelnut shoots as biofuel highlights the importance of sustainable agriculture and renewable energy production.