Biochar: A Surrogate Approach to Modulating Soil Chemical Properties and Germination Parameters of Barley Plants Grown under Multi-Stress Conditions

doi:10.21203/rs.3.rs-3216525/v1

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Biochar: A Surrogate Approach to Modulating Soil Chemical Properties and Germination Parameters of Barley Plants Grown under Multi-Stress Conditions

https://doi.org/10.21203/rs.3.rs-3216525/v1

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Background

Owing to its unique features, biochar (BC) is an excellent surrogate approach to improve the chemical properties of soil with undesirable characteristics.

Methods.

Under multiple abiotic stresses (ECe = 10.8 vs. 10.7 dS.m⁻¹; CaCO₃ = 19.1 vs. 18.8%; soil pH = 8.15 vs. 8.13) during two growing seasons (2020/2021 and 2021/2022), an experimental pot study was conducted to investigate the potential effects of palm tree frond biochar (PTF-BC) applied at three rates (0.0, 28.0, and 56.0 g.pot⁻¹, labeled as BC₀, BC₁, and BC₂) generated under three pyrolysis temperatures (350, 500, and 700 °C, labeled as PT₃₅₀, PT₅₀₀, and PT₇₀₀). The experiment was set up according to a split-plot structure in a randomized complete block design; the pyrolysis temperatures were set as the main plot and BC addition rates were set as sub-main plots.

Results.

The results indicate that PT₇₀₀ and BC₂ had the most impact on soil chemical properties, except soil pH, which was positively affected by PT₃₅₀ and BC₁. Regarding the germination parameters, the data reveal that PT₃₅₀ and P₇₀₀ were the superior treatments, while BC₂ led to noteworthy elevations of all studied germination parameters, except germination rate (GR), in both seasons. The heat map illustrating the studied soil chemical properties fluctuates between positive and negative.

Conclusion.

In short, the application of BC has profound desirable effects on soil physio-chemical properties relying on PTs.

Earth and environmental sciences/Environmental sciences

Earth and environmental sciences/Solid earth sciences

Palm-tree-frond-derived biochar

soil chemical properties

emergency barley parameters

Egypt is among the developing countries that depend on agriculture, which is considered to be the backbone of the national economy. In recent decades, the agricultural sector has faced some challenges that are impeding sustainable agricultural development. The most important of these obstacles is the widening gap between production and consumption resulting from extreme population growth (Awad et al. 2022), coinciding with limited arable land. The cultivated area in Egypt does not exceed 4% of the total area of 1,000,000 km², thus 96% of the total area is still desert land (Al-Soghir et al. 2022). In addition, there is obvious deterioration in a large part of the arable land as a result of inappropriate agricultural practices, the most important of which are salinity and calcification, which are considered major constraints to achieving the goal of sustainable agriculture (Awad and Sweed, 2020). Soil salinity has been become a major progressive environmental constraint, threatening soil quality and productivity (Yu et al. 2010), since the total area of saline soils exceeds 831 million ha and is increasing at an annual rate of 4 × 10⁴ ha globally (Saad El-Dien and Galal, 2017; Sun et al. 2018). The negative influences of salinity include nutritional imbalance and decreased osmotic stress, causing water deficit and reduce nutrient uptake (Agbna et al. 2017). At the same time, the influence of soil calcification is no less severe than that of salinity due to the undesirable effects on plant growth, including high soil pH, which causes low availability of nutrients, particularly phosphorus and micronutrients, as well as low cation exchange capacity (CEC) and soil organic matter (Aboukila et al. 2018; Wahba et al. (2019). Additional factors include the presence of impermeable layers, which hinders plant root growth, and the horizontal and vertical movement of water within the soil layers.

One of the suggested solutions to modify undesirable soil characteristics is to apply soil amendments. In the past few years, the recycling of plant-based waste to produce soil amendments, referred to as biochar (BC), has gained attention. Several studies have described BC as a stable carbonaceous organic compound produced by the pyrolysis of raw materials under conditions of limited or no oxygen (Dissanayake et al. 2020; Foong et al. 2020; Xu et al. 2021). In Egypt, especially in upper Egypt, the date palm (Phoenix dactylifera) is one of the oldest cultivated trees and the main crop. According to statistics issued by the Egyptian Economic Affairs Sector in 2018, the number of date palms was estimated at approximately 14,093,265 fruitful trees cultivated on about 47,175 ha, producing 1,563,687 metric tons. Date palm tree residue is estimated to be about 211,398,975 tons annually, with an average of 50 kg tree^− 1 of green waste (Jouiad et al. 2015). In the past, disposal of such residue was carried out by burning it in an open field, which caused increased emissions of greenhouse gases (GHGs) such as carbon dioxide (CO₂), nitrous oxide (N₂O), and methane (CH₄), which, in turn, negatively affected the environment (Singh et al. 2016; Boateng et al. 2017 and Wei et al. 2019). The presence of residual fronds is a serious problem for farmers in Egypt; thus, converting such residue to BC and applying it as a low cost and environmentally friendly material for soil amendment is an optimal solution (Yuan et al. 2019; Wu et al. 2019; Rehman et al. 2021; Malyan et al. 2021 and Haider et al. 2022).

Several studies in the literature show that BC has a multifunctional role in improving soil chemical and physical properties (Chen et al. 2019; Khan et al. 2019; Diatta et al. 2020; Mohawesh et al. 2021). In a study by Thomas and Gale (2015), they reported that the addition of biochar increased cation exchange capacity (CEC), nutrient availability, and organic carbon (OC) content, consequently improving plant growth (Sahin et al. 2017). Despite the extensive work on the impact of BC on soil properties, the available information about its effects in mitigating abiotic stresses is still somewhat scarce. However, studies by Akhtar et al. (2015a) indicated that BC is a good potential solution for salt-affected soil, because it significantly decreases salt stress, but its application increases salinity tolerance. Very recent studies mentioned that water potential, stomata conductance, and K uptake increased in BC-treated plants; moreover, BC addition reduced Na⁺ uptake and the Na⁺/K⁺ ratio in bean, potato, and quinoa plants and increased SOD, POD, and CAT activity (Ibrahim et al. 2020; Parkash and Singh, 2020; Yang et al. 2020b). Similar findings were reported by numerous researchers; She et al. (2018), and Huang et al. (2019) showed that BC incorporated into saline soil improved the availability and uptake of nutrients by wheat, bean, and quinoa plants. Moreover, BC mixed into saline soil enhanced seedling germination (Ibrahim et al. 2021). These improvement effects were attributed to BC increasing the leaf relative water content (RWC) and water use efficiency (WUE) in wheat and quinoa plants grown under saline conditions (Kanwal et al. 2018, and Nikpour-Rashidabad et al. 2019). On the other hand, some researchers noted that BC does not behave the same way in different soil textures. Kwapinski et al. (2010) and Sohi et al. (2010) noted that mixing BC into soil could hamper optimal plant growth due to the negative effect of BC on the microbial activity of soil organic matter (Koabana, 2010). Based on the above, the effect of applying BC can be between positive or negative depending on several factors, including the source of feedstock biomass and the pyrolysis temperature. However, BC can be produced from a wide range of feedstocks, such as fruit shells, plant residues (including leaves, stems, and branches), green manure, animal manure, sewage sludge, and industrial waste (Amarasinghe et al. 2016; Wang et al. 2018). Furthermore, acidic BC can be produced at low pyrolysis temperatures, while alkaline BC can be obtained at high pyrolysis temperatures (Bista et al. 2019), and the soil texture and addition rate are considered.

Therefore, our investigation included more than one purpose: to determine the optimal way to recycle and dispose of date palm fronds without polluting the environment by converting them into BC, and to take advantage of the benefits of the produced BC by possibly modifying some undesirable chemical properties of the soil.

2.1. Study location, climate conditions, timing and plant material.

In two consecutive seasons (2020/2021 and 2021/2022), two pot experiments were installed at the Faculty of Agriculture and Natural Resources, Aswan University, Egypt (24° 05´ 20"N; 32° 53´ 59"E). The aim of the study was to evaluate the effects of pyrolysis temperature on the chemical and physical properties of BC derived from palm tree (Phoenix dactylifera) fronds obtained from pruning. In addition, the potential impact of incorporating BC into soil at different rates on the soil chemical properties and barley seedling germination parameters was investigated. The average monthly (October to February) weather data in the studied location in both seasons are given in Table 1.

2.2. Source, production and characterization of BC.

Palm tree fronds (PTFs) as a feedstock biomass were collected from Edfu district, which is located about 120 km north of Aswan, Aswan Governorate, Egypt (24° 59ʹ 07ʺ N and 32° 52ʹ 38ʺ). Date palm trees are the most common crop in the study location. Collected PTFs were transferred to the Laboratory of Soil Chemistry at the Faculty of Agriculture and Natural Resources, Aswan University, and stored under ambient conditions before characterization and carbonization. They were air-dried for 7 days, ground, and placed in a sealed ceramic crucible to burn in a muffle furnace (internal dimensions 250 × 250 × 250 mm, 3000 W, electronically controlled). Before the pyrolysis process, the muffle was flushed with nitrogen for 10 min. Three pyrolysis temperatures were selected, 350, 500, and 700 °C (P₃₅₀, P₅₀₀, and P₇₀₀, respectively), for 4 h of burning at isothermal conditions in the absence of oxygen according to several previous studies (Burrell et al. 2016; Berihun et al. 2017; Mor et al. 2019). After the pyrolysis process was complete, the BC samples were sieved to small granules through a 2 mm sieve and stored in plastic bags.

2.3. Treatments, Experimental design and layout.

In both seasons of the study, DPF was utilized to produce BC at three pyrolysis temperatures (P₃₅₀, P₅₀₀, and P₇₀₀) as a main factor. Each main pot was subsequently divided into three sub-pots and three levels of biochar were applied: BC₀, BC₁, and BC₂, with 0.0, 28.0, and 56.0 g.pot⁻¹, respectively. This study was laid out according to the split-plot structure in a randomized complete block design to test the individual effects of pyrolysis temperature, addition rate, and their interaction. Details of the treatments applied in this study are given in Table 2.

2.4. Soil collections and determinations.

Soil samples were taken from the surface layer at a depth of 0-30 cm in the Sahari district, which is located in the southern part of Aswan city (latitude 22° 30ʹ and 23° 30ʹ and longitude 30° 30ʹ and 32° 00ʹ). The samples were collected over a period of 2 months, then transferred to the Soil Chemistry Analysis Laboratory (SCAL), air-dried, sieved through a 2 mm sieve, and kept in plastic containers prior to soil chemical and physical analysis, as shown in Table 3. Soil particle distribution was determined by the hydrometer method, as described by Gee and Bauder (1986). Soil reaction (pH) was measured in saturated soil paste using a pH meter (Jenway, UK) according to Thomas (1996). ECe, a salinity indicator, was measured in saturated soil paste extract, as described by Blume et al. (1982), using an EC meter (LF-191 Condukometer, Germany).

Using the Collins calcimeter method, the CaCO₃ content was determined as described by Page et al. (1982). Soil organic matter (SOM) content was determined by using the wet digestion method according to Walkey and Black (1934), as described by Nelson and Sommers (1982). Soluble cations (Na⁺, K⁺, Ca⁺⁺, and Mg⁺⁺) were extracted with 1 N NH₄AOC at pH 7.0 (W/V), left to sit overnight, and filtered with No. 42 Whatman paper. The resting and filtration of the extract were repeated until completed to a final volume of 100 mL with distilled water. Using flame photometry, K⁺ and Na⁺ were measured as described by Jackson (1973), while Ca⁺⁺ and Mg⁺⁺ were measured with the titration method using EDTA. Soluble anions (CO₃⁻⁻, HCO₃⁻, Cl⁻, and SO₄^—) were measured by the titration method according to McLean (1982). The cation exchange capacity (CEC) was measured according to the micro-Kjeldahl method as described by McLean (1982) by extracting 1 M NH₄AC (pH 7.0), then leaching the NH₄AC with 10% sodium chloride (NaCl) and measuring. Na⁺ ions replaced the NH₄⁺ ions, then the amount of NH₄⁺ ions in the percolate was determined. The produced BC samples were analyzed for their ammoniacal nitrogen (NH₄⁺-N) content.

Soil NH₄-N was determined using a 2 M KCl extract solution, and samples were examined by a spectrophotometer according to Keeney and Nelson (1983). Soil P was calculated by spectrophotometric analysis, using NaHCO₃ solution (0.5 M) as an extractant (Olsen, 1982). K concentration was measured on a ﬂame photometer, with 1 N ammonium acetate solution used to run the samples (Helmke et al. 1996). Micronutrients in the soil were determined by using the AB-DTPA extraction method (Soltanpour and Schwab, 1977).

2.5. BC characterization

The characterization of palm-tree-frond-derived BC at different pyrolysis temperatures (350, 500, and 700 °C) was performed using several analytical techniques. Elemental analysis, including the C, O, P, K, Ca, Mg, Cl, and Si content of biochar, was conducted using energy dispersive X-ray (EDX) (Elementar Analysensysteme GmbH, Langenselbold, Germany). Scanning electron microscopy (SEM) was used to determine the morphology of BC samples. Additionally, Fourier transform infrared spectroscopy (FT-IR) with a Bruker Vertex 80v was used to identify the chemical functional groups present in the BC samples.

2.6. Germination parameters.

Germination percentage (G%) was determined by a formula presented by Close and Wilson (2002): G% = \(\frac{\text{N}\text{u}\text{m}\text{b}\text{e}\text{r} \text{o}\text{f} \text{s}\text{e}\text{e}\text{d}\text{s} \text{g}\text{e}\text{r}\text{m}\text{i}\text{n}\text{a}\text{t}\text{e}\text{d} \text{d}\text{u}\text{r}\text{i}\text{n}\text{g} \text{t}\text{i}\text{m}\text{e} \text{i}\text{n}\text{t}\text{e}\text{r}\text{v}\text{a}\text{l}}{\text{T}\text{o}\text{t}\text{a}\text{l} \text{n}\text{u}\text{m}\text{b}\text{e}\text{r} \text{o}\text{f} \text{s}\text{e}\text{e}\text{d}\text{s} \text{s}\text{o}\text{w}\text{n}}\) x 100.

Seed vigor (SV) of the barley seedlings was measured by a formula presented by Abdul and Andersson (1973): SV = \(\frac{\text{G}\text{e}\text{r}\text{m}\text{i}\text{n}\text{a}\text{t}\text{i}\text{o}\text{n} \text{p}\text{e}\text{r}\text{c}\text{e}\text{n}\text{t}\text{a}\text{g}\text{e} \times \text{m}\text{e}\text{a}\text{n} \text{s}\text{e}\text{e}\text{d}\text{l}\text{i}\text{n}\text{g} \text{l}\text{e}\text{n}\text{g}\text{t}\text{h} }{100}\) .

Germination rate (GR) was determined by a formula presented by Khan and Ungar (1984): GR = \(\frac{\text{F}\text{i}\text{r}\text{s}\text{t} \text{d}\text{a}\text{y} \text{o}\text{f} \text{s}\text{e}\text{e}\text{d} \text{g}\text{e}\text{r}\text{m}\text{i}\text{n}\text{a}\text{t}\text{i}\text{o}\text{n}}{\text{T}\text{o}\text{t}\text{a}\text{l} \text{n}\text{u}\text{m}\text{b}\text{e}\text{r} \text{o}\text{f} \text{s}\text{e}\text{e}\text{d}\text{s} \text{s}\text{o}\text{w}\text{n}}\) x 100.

2.7. Statistical analysis.

Using the Genstat statistical package version 12, analysis of variance (ANOVA) and Duncan’s test were performed. Correlation was determined by the calculation of Pearson’s linear correlation coefficient (r).

3.1. Characterization of BC samples.

Figure (1, 1A-1C) shows the morphology of BC obtained from palm tree fronds (PTF-BC) under pyrolysis temperatures of 350, 500, and 700 °C (PT₃₅₀, PT₅₀₀, and PT₇₀₀, respectively) by scanning electron microscopy (SEM). Visual inspection of images (at different magnifications) revealed differences in irregular porous surfaces. Pores were observed in all BC samples, with higher numbers and greater distribution in PT₅₀₀ and PT₇₀₀ compared to PT₃₅₀. On the contrary, there was a greater volume of pores in PT₃₅₀ than in PT₅₀₀ and PT₇₀₀.

The results presented in Table 4 show the chemical properties, elemental composition, and molecular ratios of PTF-BC samples under the three pyrolysis temperatures (PT₃₅₀, PT₅₀₀, and PT₇₀₀) using energy dispersive EDX analysis. Our results indicate that the pH of all biochar obtained was, in general, alkaline. The BC pH increased with increasing pyrolysis temperature; the pyrolysis temperatures were ranked in descending order as PT₇₀₀ (11.68) > PT₅₀₀ (9.76) > PT₃₅₀ (9.15). Like BC pH, the cation exchange capacity (CEC) of BC samples increased with increasing pyrolysis temperature. As shown in Table 4, the highest (47.15 cmol.kg⁻¹) and lowest (44.89 cmol.kg⁻¹) values were recorded for BC samples in PT₇₀₀ and PT₃₅₀, respectively. On the contrast, BC electrical conductivity (EC) declined with increasing pyrolysis temperature. The values of BC EC decreased in PT₅₀₀ and PT₇₀₀ by approximately 27.18 and 34.19%, respectively, compared with PT₃₅₀. Carbon (C) content is a major constituent of BC. The results obtained reveal that the C content increased with increasing pyrolysis temperature. The pyrolysis temperatures were ranked in descending order as PT₇₀₀ (63.14) > PT₅₀₀ (58.45) > PT₃₅₀ (57.77). Similarly, the nitrogen (N) content in BC was positively correlated with pyrolysis temperature. As shown in Table 4, the N content increased by 90.91 and 50% in PT₇₀₀ and PT₅₀₀, respectively, compared with PT₃₅₀.

The oxygen content in BC decreased with rising pyrolysis temperature, and the studied pyrolysis temperature could be arranged in the order PT₃₅₀ (15.40) > PT₅₀₀ (10.10) > PT₇₀₀ (7.30). Negligible increases were observed in phosphorus (P) content of BC samples, with 0.106, 0.113, and 0.164 in PT₃₅₀, PT₅₀₀, and PT₇₀₀, respectively. On the contrary, the potassium (K)_content was significantly increased with increasing pyrolysis temperature. In addition, there were adequate quantities of calcium (Ca), magnesium (Mg), chloride (Cl), and silicon (Si) in the prepared BC. As shown in Table 4, the molecular ratios of elements, which determine polarity (O/C) and (O+N/C), were appreciably influenced by pyrolysis temperature, and the BC samples were significantly affected by PT, as shown in Table 5. PT was ranked in descending order as PT₃₅₀ > PT₅₀₀ > PT₇₀₀, with values of 0.1999 > 0.1296 > 0.0866 for O/C and 0.1323 > 0.1622 > 0.2272 for (O+N)/C.

3.2. Soil chemical properties and available nutrients content.

3.2.1. Impact of pyrolysis temperature.

As shown in Table 3, the tested soil was characterized as moderately alkaline (pH 8.15 vs. 8.13) loamy sand soil with a high content of salt (ECe = 10.8 vs. 10.7 dS.m⁻¹) and calcium carbonate (CaCO₃ = 19.1 vs. 18.8%) in the 2020/2021 and 2021/2022 seasons. The results given in Table 5 indicate the impact of pyrolysis temperature (PT) on some soil chemical properties. Our results show that low pyrolysis temperature (PT₃₅₀) applied to produce BC from palm tree fronds (PTF-BC) was the best for soil reactivity (soil pH) in both seasons. On the contrary, high pyrolysis temperature (PT₇₀₀) was superior for ECe, CaCO₃, SOM, and CEC in both seasons. As shown in Table 5, the best values of soil pH (8.14 vs. 8.12) were obtained with PT₃₅₀. On the other hand, PT₇₀₀ had the most influence on Ece (6.00 vs. 6.22 dS.m⁻¹) and CaCO₃ (11.79 vs. 11.86%) (decreasing). It also had an influence on SOM (1.89 vs. 1.94%) and CEC (12.56 vs. 12.53 Cmol.kg⁻¹) (increasing) for both properties in the first and second seasons. Based on the maximum and minimum values, the decreases were 2.63 vs. 2.74% for soil pH, 42.20 vs. 39.73% for ECe, and 37.49 vs. 37.08% for CaCO₃. The increases were 37.96 vs. 28.48% for SOM and 73.00 vs. 70.01% for CEC in both seasons. The results of the statistical analysis showed significant differences among all studied parameters (p ≤ 0.01) in the 2020/2021 and 2021/2022 seasons.

As shown in Table 6, our results indicate that PT₇₀₀ had the most impact on available soil nutrient content in both seasons, except manganese (AvMn) in the first season. Similar data were found for NH₄⁺-N, AvP, AvK, and AvFe, and the pyrolysis temperatures were ranked in descending order as PT₇₀₀ > PT₅₀₀ > PT₃₅₀, with values of 12.45 > 7.67 > 4.73 and 11.67 > 9.34 > 5.06 for NH4+-N, 6.02 > 5.49 > 5.46 and 10.92 > 9.60 > 8.58 for AvP, 112.67 > 118.89 > 108.00 and 312.67 > 279.11 > 260.67 for AvK and 3.52 > 3.28 > 2.88, and 3.70 > 3.68 > 3.18 for AvFe in the two seasons; for AvZn, the order is PT₇₀₀ > P₃₅₀ > PT₅₀₀, with values of 1.32 > 1.30 > 1.22 and 1.67 > 1.58 > 1.57 in both seasons. Different data were obtained between seasons in terms of AvMn, and the pyrolysis temperatures were arranged in the following order: PT₃₅₀ (1.65) > PT₅₀₀ (1.60) > PT₇₀₀ (1.58) in the first season and PT₇₀₀ (1.42) > PT₅₀₀ (1.35) > PT₃₅₀ (1.33) in the second season. Based on the highest and lowest values, the amount of increase was 163.21 vs. 130.83% for NH4+-N, 10.26 vs. 27.27% for AvP, 4.32 vs. 19.95% for AvK, 22.22 vs. 16.35% for AvFe, 4.43 vs. 6.77% for AvMn, and 8.20 vs. 6.37% for AvZn in both seasons. The analysis of variance indicated a significant (p ≤ 0.01) influence of NH₄⁺-N in both seasons, and a significant (p ≤ 0.05) influence of AvFe and AvZn in the second season, but a non-significant influence of AvP and AvK in the first season and AvMn in both seasons. The results produced from the statistical analysis mentioned significant differences among all studied parameters (at p ≤ 0.01) in the 2020/2021 and 2021/2022 seasons, respectively.

As shown in Table 6, our results indicate that PT₇₀₀ had the most impact on available soil nutrient content in both seasons, except manganese (AvMn) in the first season. Similar data were found for NH₄⁺-N, AvP, AvK, and AvFe, and the pyrolysis temperatures were ranked in descending order as PT₇₀₀ > PT₅₀₀ > PT₃₅₀, with values of 12.45 > 7.67 > 4.73 and 11.67 > 9.34 > 5.06 for NH4+-N, 6.02 > 5.49 > 5.46 and 10.92 > 9.60 > 8.58 for AvP, 112.67 > 118.89 > 108.00 and 312.67 > 279.11 > 260.67 for AvK and 3.52 > 3.28 > 2.88, and 3.70 > 3.68 > 3.18 for AvFe in the two seasons; for AvZn, the order is PT₇₀₀ > P₃₅₀ > PT₅₀₀, with values of 1.32 > 1.30 > 1.22 and 1.67 > 1.58 > 1.57 in both seasons. Different data were obtained between seasons in terms of AvMn, and the pyrolysis temperatures were arranged in the following order: PT₃₅₀ (1.65) > PT₅₀₀ (1.60) > PT₇₀₀ (1.58) in the first season and PT₇₀₀ (1.42) > PT₅₀₀ (1.35) > PT₃₅₀ (1.33) in the second season. Based on the highest and lowest values, the amount of increase was 163.21 vs. 130.83% for NH4⁺-N, 10.26 vs. 27.27% for AvP, 4.32 vs. 19.95% for AvK, 22.22 vs. 16.35% for AvFe, 4.43 vs. 6.77% for AvMn, and 8.20 vs. 6.37% for AvZn in both seasons. The analysis of variance indicated a significant (p ≤ 0.01) influence of NH₄⁺-N in both seasons, and a significant (p ≤ 0.05) influence of AvFe and AvZn in the second season, but a non-significant influence of AvP and AvK in the first season and AvMn in both seasons.

3.2.2. Impact of biochar addition rate on soil chemical properties and available nutrient contents.

The data listed in Table 7 highlight the impact of BC addition rates on soil chemical properties. The general trend of the results shown in the table clearly indicate improvements by incorporating BC at 56.00 g.pot⁻¹ (BC₂), followed by 28.00 g.pot⁻¹ (BC₁), compared with un-amended soil (BC₀). For soil pH, the BC addition rate was ranked in descending order as BC₁ (8.23) > BC₂ (8.24) > BC₀ (8.25) and BC₂ (8.21) > BC₁ ≈ BC₀ (8.24) in the first and second seasons, respectively, and BC₂ > BC₁ > BC₀, with values of 6.57 > 8.32 > 8.75 and 6.96 > 8.15 > 9.01 for ECe, 14.25 > 15.34 > 16.01 and 14.40 > 15.36 > 16.14 for CaCO₃, and 10.49 > 10.25 > 10.15 and 10.50 > 10.27 > 10.25 for CEC in both seasons.

According to the comparison between maximum and minimum values, the increase rates were 0.24 vs. 0.37% for soil pH, 33.18 vs. 29.45% for Ece, 12.35 vs. 12.08% for CaCO₃, 4.97 vs. 5.26% for SOM, and 3.50 vs. 2.37% for CEC in the 2020/2021 and 2021/2022 seasons, respectively. The results of ANOVA indicate that the BC addition rate had a significant influence (p ≤ 0.01) on Ece and CaCO₃ in both seasons, and on CEC in the second season, as well as a significant impact (p ≤ 0.05) on CEC in the first season but a non-significant effect on soil pH and SOM in the first and second seasons. It is clear from Table 8 that BC-based soil led to marked enhancements in soil fertility by increasing their macro- and micronutrient content. The results obtained from our experimental pot study indicate that applying BC, in general, improved the content of all studied nutrients in both seasons, except AvFe (3.30) in the second season, irrespective of addition rate. However, the statistical analysis showed non-significant effects on AvP, AvFe, and AvZn in both seasons and NH₄⁺-N, AvK, and AvMn in the first season.

In detail, different results were obtained for NH₄⁺-N and AvFe. We found that BC₂ treatment resulted in the highest value for NH₄⁺-N (9.73) in the second season and for AvFe (3.33) in the first season. Meanwhile, BC₂ was found to have the most impact on AvP (5.67 vs. 9.77), AvK (115.11 vs. 288.00), and AvMn (1.65 vs. 1.43), as well as AvFe (3.33) in the first season. The highest AvZn values (1.30 vs. 1.63) were obtained with BC₁. Our results also indicate that BC₀ had the least influence on NH₄+-N and AvP in both seasons, AvFe and AvZn in the first season, and AvK in the second season.

3.2.3. Impact of pyrolysis temperature x BC-addition rate on soil chemical properties and available nutrients content.

The results given in Table 9 show that all of the aforementioned chemical properties, except soil pH, were greatly improved by the interaction between pyrolysis temperature and BC addition rate. In this paper, BC heated at 700 °C at 56.00 g.pot⁻¹ (PT₇₀₀ × BC₂) provided the best treatment due to its positive influence on ECe and CaCO₃ (which decreased) and CEC (which increased) in both seasons. The results related to soil pH and SOM do not match between seasons. Regarding soil pH, the highest values (8.13 vs. 8.09) were recorded in un-amended soil (PT₃₅₀ × BC₀) and soil incorporated with BC heated at 500 °C at 56.00 g.pot⁻¹ (PT₅₀₀ × BC₂) in the 2020/2021 and 2021/2022 seasons, respectively.

The application of BC heated at 700 °C at 56 and 28.00 g.pot⁻¹ (PT₇₀₀ × BC₂ and PT₇₀₀ × BC₁) had the most influence on SOM, with values of 1.90 and 2.00% in the first and second seasons, respectively. Based on the highest and lowest values obtained (Table 9), the decrease rates were 2.87 vs. 3.11% for soil pH, 63.70 vs. 62.81% for ECe, and 44.86 vs. 43.55% for CaCO₃, while the values reached 46.15 vs. 39.86% for SOM and 79.81 vs. 79.20% for CEC in the two seasons. Statistically, highly significant effects were found between treatments for Ece and CaCO₃ in both seasons and CEC in the second season, while non-significant effects were observed between treatments for soil pH and SOM in the first and second seasons, and for CEC in the 2020/2021 season.

The results regarding the impact of the interaction of pyrolysis temperature with BC addition rate are shown in Table 10. The general trend indicates that this interaction improved the content of all studied macro- and micronutrients, except AvFe and AvMn in the second season. However, the PT₇₀₀ × BC₂ treatment shows the most influence, with the highest NH₄⁺-N content (14.01 vs. 13.95 mg.kg⁻¹) in both seasons, as well as AvP and AvMn in the first season (8.96 vs. 1.80 mg.kg⁻¹) and AvZn in the second season (1.90 mg.kg⁻¹). Furthermore, the PT₇₀₀ × BC₁ treatment was found to be superior, showing a positive effect on AvK in both seasons (276.67 vs. 316.67 mg.kg⁻¹), as well as AvFe (3.90 mg.kg⁻¹) and AvZn (1.40 mg.kg⁻¹) in the first season and AvP (11.05 mg.kg⁻¹) in the second season. Despite the observed enhancements, the statistical analysis indicated that the treatment had a non-significant influence on AvP and AvK in both seasons, and on NH₄⁺-N, AvFe, and AvZn in the first season and AvMn in the second season. Meanwhile, it showed a significant (p ≤ 0.01) impact on AvFe and AvZn in the second season and a significant ( p ≤ 0.05) impact on AvMn in the first season.

3.2.4. The heat map of correlation coefficient.

The data shown graphically in Figure (2, 2A and 2B) indicate the correlation coefficient between soil physical properties as a result of applying BC generated under three pyrolysis temperatures at different rates. A highly negative correlation was found between pH and Ece (r = -0.779** and -0.705**) and CaCO₃ (r = -0.920** and -0.869) in both seasons. Meanwhile, soil pH showed a strong positive correlation with SOM (r = 0.854** and 0.802**) and CEC (r = 0.926** and 0.888**) CEC in the first and second seasons. Concerning the correlation coefficient for available macro- and micronutrients as affected by other soil chemical properties, our results indicate that soil pH had a highly significant positive impact on NH₄⁺-N (r = 0.834** and 0.802**) in both seasons, and a profound effect on AvFe (r = 0.601**) in the first season and AvP and AvK (r = 0.901** and 0.857**) in the second season. On the other hand, ECe had a strong negative correlation with NH₄⁺-N (r = -0.796** and -0.892**) in both seasons and AvFe (r = -0.526**) in the first season, as well as AvP and AvK (r = -0.710 and -0.726**) in the second season. Similar results were obtained regarding the relationship between CEC and available nutrient content. Highly significant positive correlations were found with NH4+-N (r = 0.837** and 0.840**) and AvFe (r = 0.574** and 0.594**) in both seasons. In the present study, a significant correlation (p ≤ 0.01) was observed between CEC and both AvP (r = 0.890**) and AvK (r = 0.594**) in the 2021–2022 season and a significantly correlation (p ≤ 0.05) between CEC and AvP (r = 0.382*) in the first season. Regarding the relationships among available nutrients, a strong positive correlation was observed between NH₄⁺-N and both AvP and AvK (r = 0.759** and 0.776**) in the second season and with AvFe (r = 0.359**) in the first season. Similar results were obtained between AvP and AvFe (r = 0.467*) in the second season and AvZn (r = 0.383*) in the first season. Regarding the relationships among available nutrients with them. A strong positive correlation were observed between NH₄⁺-N with AvP and AvK (r = 0.759** and 0.776**) in the second season and with AvFe (r = 0.359**) in the first season. Similar results were obtained between AvP with AvFe (r = 0.467*) in the second season and AvZn (r = 0.383*) in the first season.

3.3. Germination parameters

3.3.1. Effect of pyrolysis temperature on some germination parameters.

The results related to the impact of the pyrolysis temperature of palm-tree-frond-derived BC on germination parameters are graphically demonstrated in (Figure 3, 3A-3D). The general trend of the results shows that PT₇₀₀ had the most influence on germination rate in both seasons, and on germination percentage and mean emergence time (MET) the second season. Pyrolysis temperature was ranked in descending order as PT₇₀₀ (28.52 vs. 26.39) > PT₅₀₀ (22.24 vs. 23.30) > PT₃₅₀ (20.75 vs. 21.72) for GR in both seasons, and PT₇₀₀ (54.59) > PT₅₀₀ (48.89) > PT₃₅₀ (46.67) for GP and PT₇₀₀ (0.33) > PT₅₀₀ (0.27) > PT₃₅₀ (0.26) for MET in the 2021–2022 season. On the other hand, PT₃₅₀ had the most impact due to its improved effect on seed vigor (SV) in both seasons and on GP and MET in the first season. Pyrolysis temperature was ranked as PT₃₅₀ (2067.42 vs. 1834.74) > PT₅₀₀ (1853.33 vs. 1626.30) > PT₇₀₀ (1783.70 vs. 1562.90) for SV in the first and second season, and similarly for GP and MET, with values of 68.90 > 57.78 > 45.20 for GP and 0.33 > 0.27 > 0.26 for MET in the 2021/2022 season.

The results of statistical analysis clearly indicate a significant difference (p ≤ 0.01) for SV in both seasons and for GP and GR in the first season, as well as a significant impact (p ≤ 0.05) for GP in the second season and MET in the first season. Furthermore, non-significant differences were observed between treatments for GR and MET in the 2021/2022 season.

3.3.2. Influence of BC addition rate on germination parameters

The results of statistical analysis show that the BC addition rate had a highly significant influence on the germination parameters. As graphically illustrated in (Figures 4, 4A-4D), the amended soil in BC₂ had the best values for GP, SV, and MET compared with un-amended soil (BC₀) in the two growing seasons. The BC addition rates were ranked in descending order as BC₂ > BC₁ > BC₀, with values of 75.55 > 59.63 > 45.20 and 54.59 > 48.89 > 49.67 for GP, 3000.74 > 1405.18 > 1398.52 and 2571.11 > 1324.37 > 1228.52 for SV, and 0.42 > 0.34 > 0.25 and 0.35 > 0.33 > 0.27 for MTE in the 2020/2021 and 2021/2022 seasons, respectively.

Different results were obtained between seasons for GP, with BC₀ and BC₁ showing the least influence. We found the highest values (20.45 vs. 23.20) with BC₀ and BC₁ in the two growing seasons. On the contrary, the lowest value (17.19) was found for BC₁ in the first season and un-amended soil in the second season.

3.3.3. Interaction of pyrolysis temperature and BC addition rate

The results regarding the effect of the interaction between pyrolysis temperature and BC addition rate on germination parameters of barley seedlings grown in sandy loam clay soil characterized by undesirable properties are presented in Table 11. During the first season, it was found that applying BC heated at 700 °C at 56 g.pot (PT₇₀₀ × BC₂) was the best treatment for GP, SV, and MET, with values of 86.78%, 39.00, and 0.47, respectively. Meanwhile, the PT₃₅₀ × BC₀ treatment showed the highest value for VI at 389.06. Similarly, the results show the minimum values for all germination parameters for PT₇₀₀ × BC₀, with values of 24.44, 4.53, 32.12, and 0.14 for GP, SV, VI, and MET, respectively. The results for the highest values were not the same in the second season. It was observed that adding BC heated at 350 °C (PT₃₅₀ × BC₁) at a rate of 28 g.pot was the optimal treatment for GP and VI, with values of 71.11% and 113.78, respectively. Soil amended with BC heated at 500 °C at a rate of 56 g.pot (PT₅₀₀ × BC₂) and at 350 °C at 56 g.pot (PT₃₅₀ × BC₂) recorded the best values for SV and EMT at 20.20 and 0.42, respectively. On the other hand, the lowest values for the studied germination parameters were found with PT₃₅₀ × BC₀, at 20.00, 4.07, 20.08, and 0.11 for GP, SV, VI, and MET, respectively. The increases amounted to 255.07 vs. 255.55%, 760.93 vs. 396.31%, 1111.27 vs. 466.63%, and 235.71 vs. 281.81% for GP, SV, VI, and MET in the 2019–2020 and 2020–2021 seasons, respectively. The analysis of variance showed that there were significant differences (P ≥ 0.01) for all germination parameters in both growing seasons, except SV in the second season (no significant effects).

As is long known, date palm trees are among the oldest cultivated plants in Egypt, producing huge amounts of waste including fronds, offshoots, and date pits. According to Jouiad et al. (2015), such trees generate about 50 kg of waste annually. Until recently, the waste has been disposed of by burning in open fields, resulting in increased emission of greenhouse gases (GHGs), including carbon dioxide (CO₂), nitrous oxide (N₂O), and methane (NH₄), which negatively affects the environment. In the past two decades, the conversion of plant- and animal-based waste into a carbon-rich substance known as biochar (BC) has received a great amount of attention based on its unique features (Tian et al. 2020). Although numerous studies have examined its effect on different soil properties, most of them did not deal with its behavior in soils with undesirable characteristics. Generally speaking, the influence (positive or negative) on soil properties is associated with factors such as feedstock biomass type, pyrolysis temperature, heating rate, soil type, and BC application rates (Arif et al. 2017; Gluszek et al. 2017 and El-Naggar et al. 2018). Our pot experiment was carried out under multiple abiotic stresses, representing a high content of salts (10.8 vs. 10.7 dS.m^− 1) and CaCO₃ (19.1 vs. 18.8%), as well as high soil reactivity (8.15 vs. 8.13) in two seasons (Table 2), in order to investigate the potential impact of pyrolysis temperature on the physicochemical properties of the BC produced. The effect of pyrolysis temperature on palm tree fronds (PTFs) to generate BC was explored by using analytical techniques, including energy-dispersive X-ray (EDX) to determine the elemental composition.

The general trend of our results indicates that C is a major constituent that increases with increasing pyrolysis temperature. This may due to the high carbonization and thermochemical decomposition of feedstock biomasses at high pyrolysis temperatures (Singh et al. 2017). On the contrary, the decreased oxygen (O) and hydrogen (H) content with higher PT could be due to the removal of moisture, hydrocarbons, and gases, such as H₂, CO₂, and CO (Chun et al. 2004). These results are supported by some recent studies (Frikha et al. 2021; Huang et al. 2021; Ghorbani et al. 2022 and Tu et al. 2022). Another possible explanation is that high pyrolysis temperature (HPT) could cause cracking of weak bonds in prepared BC (Sun et al. 2014). The mineral analysis revealed that both FS and PT appreciably affected the phosphorus (P), calcium (Ca), and magnesium (Mg) content (which increased). The positive relationship between PT and Ca content could be ascribed to the presence of insoluble CaCO₃ and its calcination into soluble calcium oxide (Usman et al. 2015). Furthermore, Mg is present in magnesium oxide and insoluble periclase (Lehmann and Joseph, 2015). Several studies indicated that the content of these elements in BC is significantly influenced by the type of biomass used to produce it. It can be seen that P content is positively affected by HPT. For example, Xiao et al. (2018) and Li et al. (2020) reported that available P increased with increasing PT. However, the Ca content in crop residue derived BC ranged between 0.20 and 1.57% (Prakongkep et al. 2015; Abujabhah et al. 2016 and Arif et al. 2016) and Mg content ranged between 0.001 and 3.78% (Wrobel-Tobiszewska et al. 2015; Yu et al. 2017 and Zhao et al. 2018). On the other hand, potassium (K) content is negatively influenced by the feedstock. In addition, there are adequate amounts of silicon (Si) and chloride (Cl) due to the presence of metallic oxides in BC samples (Singh et al. 2017). The large variation of K content was also associated with the feedstock type, which is likely due to the concentration effect (Xiao et al. 2018). Our results indicate that both feedstock biomass and pyrolysis temperature played pivotal roles in determining the elemental composition and properties of BC. These results are in agreement with previous reports of Joseph and Taylor (2014), Yargicglu et al. (2015), Laghari et al. (2016), and Yuan et al. (2017). Scanning electron microscopy (SEM) is another technique used to determine the morphology of BC samples. As shown in (Figs. 1, A-C), all BC samples had a smooth surface, and the pores were more visible.

Our pot experiment clearly indicated that pyrolysis temperature significantly affected soil chemical properties regardless of the BC addition rate, depending on the influence of pyrolysis temperature on BC chemical and physical properties. As shown in Table 6, PT₃₅₀ was found to have the most influence on soil pH (which decreased) compared to PT₅₀₀ and PT₇₀₀. These results could be attributed to the increase in basic oxides and carbonates produced during the pyrolytic process (Alazzaz et al. 2020). These results are in line with previous studies (Cardelli et al. 2017; Yao et al. 2017 and Tang et al. 2019), which reported that soil pH increased with increasing pyrolysis temperature. In this respect, Singh et al. (2020) noted that functional groups, such as carboxyl, formyl, and hydroxyl groups, could be removed under high pyrolysis temperatures, along with increased inorganic element concentrations and basic oxides. In other words, the high pH of the BC samples could be attributed to the presence of alkali, and alkali metals are not volatilized during the pyrolysis process (Yang et al. 2018). On the other hand, PT₇₀₀ had the most impact on other soil properties: EC and CaCO₃ (which decreased) and SOM and CEC (which increased). The appreciable decreases in EC were explained by the inverse relationship between EC and PT. However, EC decreased with increasing PT, as shown in Table 4. Meanwhile, the slight increase in SOM content could be due to increased C content of BC produced with higher heating temperature; C is a basic element in the BC structure (varying between 40 and 75%) and is not easily broken down by microorganisms (Tan et al. 2015). In addition, there was a marked increase in CEC. The high pyrolysis temperature increases the surface area and porosity of palm tree fronds, in turn increasing the concentrations of minerals such as K, P, Ca, and Mg on the adsorbent surface, which increases CEC (Sun et al. 2014). These results align with those of Lehmann and Joseph (2015). In other words, the functional groups, including carboxyl, hydroxyl, and amino groups, have a profound influence on increasing the adsorption of minerals (Zbair et al. 2019).

Concerning the effect of pyrolysis temperature on available soil macronutrients (N, P, and K) and micronutrients (Fe, Mn, and Zn), the results revealed that the TN content of BC increased with increasing pyrolysis temperature, and pyrolysis treatments were ranked in descending order as PT₇₀₀ (4.20%) > PT₅₀₀ (2.80%) > PT₃₅₀ (2.20%). These findings may be attributed to the residence time of pyrolysis; in addition, the N-containing component of BC can be present on the surface or inside the pores as nitrates, ammonium salts, or heterocyclic compounds (Grierson et al., 2011). These results agree with those of Chang et al. (2015), who found that N content in Chlorella-based algal waste BC increased from 10.23 to 14.12% when the time pyrolysis time at 500°C was increased from 20 to 60 min. Similar results were reported by Zhu et al. (2016), who noted that inorganic N forms such as NH₄-N and NO₃-N increased when biomass was heated at 800°C, whereas the same forms decreased when it was heate4d at 300°C. As with N content, the increased P content with increasing pyrolytic temperature could be due to the “concentration impact” as a result of decreased BC yield with increasing temperature. These findings agree with those of Xiao et al. (2018), who found that P content increased by 1.91, 2.15, and 2.96% when pyrolysis temperature was increased to 250, 350, and 550°C, respectively, for production of BC from chicken manure. In general, P content varies between 0.005 and 5.9% depending on the type of feedstock. For instance, studies have reported P content of 5.9% in BC derived from swine solids (Cantrell et al, 2012), 2.96% in BC produced from chicken manure (Xiao et al., 2018), and 2.57% in BC produced from poultry manure (Brantley et al., 2016). Similar results were obtained for K content, which depended on biomass type and pyrolysis temperature. High K content was explained by to the concentration impact. For example, the K content in BC produced from poultry manure increased from 3.88 to 5.88% when the heating temperature was increased from 400 to 600°C (Subedi et al. 2016). Vaughn et al. (2018) reported K values of 3.89, 3.98, 4.06, 4.02, 8.12, and 9.83 for biosolid-derived BC at 300, 400, 500, 700, and 900°C, respectively.

The results regarding the influence of BC addition rate on soil chemical properties show that incorporating BC at any application rate improved all chemical properties of the studied soil. It was found that BC₂ was the best treatment for all studied properties, except soil pH in the first season, which was influenced by BC₁ (Table 7). The slight enhancement in soil pH could be attributed to oxidation and the generation of acidic materials in the BC during pyrolysis (Zhang et al. 2019). In their study, Lee et al. (2013) noted that the pH of BC depends on three factors: organic functional groups, carbonate content, and inorganic alkali content. Similar results were reported by Cheng et al. (2018), who supposed that the slight decrease in soil pH could be attributed to organic acids obtained during the pyrolysis of palm tree fronds affecting the pH of the final BC. Furthermore, the pH of BC was positively correlated with pyrolysis temperature. Our results show that the slight increase in soil pH was related to increased pyrolysis temperature and BC addition rate. BC is alkaline in its nature, and the alkalinity rises with increased heating temperature during pyrolysis, as shown in Table 4. This could be attributed to some acidic functional groups being removed at higher pyrolysis temperatures, subsequently increasing basic oxides and inorganic elements (Shakya and Agawal, 2018 and Singh et al. 2020). These findings agree with those of Hossain et al. (2022), who reported pH levels of BC ranging from 6.52–12.64. In other words, the high pH of BC could be due to the presence of alkali, and alkali metals are not volatilized during the pyrolysis process (Yang et al. 2018). This view was opposed by Li et al. (2017), who reported that at high pyrolysis temperature, the concentrations of these functional groups decreased. In this regard, Igalavithana et al. (2018) reported that the EC of most BC is higher than that of other agricultural amendments due to its high content of soluble salts such as NO₃⁻, K⁺, and Ca²⁺ which might increase the EC of agricultural soils. CEC is one of the most influential properties affecting soil fertility because of the high adsorptive capacity of positive ions and mineral nutrients in the soil (Sohi et al. 2010), although CEC in most soils is a natural and inherent property, and accordingly it does not change. However, our results show that the soil CEC increased with higher BC addition rates due to the presence of negative charges on the surface of BC due to the presence of strong of carboxyl and phenolic functional groups (Tian et al. 2017 and Palansooriya et al. 2019). Similar results were reported by Gao et al. (2017), Pandit et al. (2018), and Karimi et al. (2020), who documented that BC application increased soil CEC.

As previously mentioned in the literature, BC is a nutrient source for crop plants, and the nutrient content in BC mainly depends on the feedstock biomass and pyrolysis conditions (El-Naggar et al. 2019a). For instance, the N content of BC can vary between 0.24 and 6.8% based on the biomass type. Studies have reported N content of 6.8% in BC derived from sewage sludge (Gonzaga et al. 2019), 5.85% in BC from poultry litter (Macdonald et al., 2014), and 4.9% in BC from grass waste (Enders et al. 2012). Contrary to our results, N content in BC was reported to decline with increased pyrolysis temperature due to the conversion of amino acids into pyridine-N and pyrrolic-N (Leng et al. 2020). Moreover, a loss of NH₄⁺-N as NH₃ gas through the pyrolysis process has also been reported (El-Naggar et al. 2019a).

The results revealed that the N content of soil incorporated with BC increased when the pyrolysis temperature was higher. This may be attributed the residence time of pyrolysis; in addition, the N-containing component of BC can be present on the surface or inside the pores as nitrates, ammonium salts, or heterocyclic compounds (Grierson et al. 2011). These results agree with those of Chang et al. (2015), who found that N content in BC derived from Chlorella algal waste increased from 10.23 to 14.12% when pyrolysis time at 500°C was increased from 20 to 60 min. Similar results were reported by Zhu et al. (2016), who noted that inorganic N forms such as NH₄⁺-N and NO₃⁻-N increased when the biomass was heated at 800°C, whereas they decreased when it was heated at 300°C. Similar to N content, the increased P content with higher pyrolytic temperatures could be due to the “concentration impact” as a result of decreased BC yield with increasing pyrolysis temperature. These findings agree with those of Xiao et al. (2018), who found that P content increased by 1.91, 2.15, and 2.96% when the pyrolysis temperature was increased to 250, 350, and 550°C, respectively, for production of BC from chicken manure. In general, P content varies between 0.005 and 5.9% based on the type of feedstock. Studies have reported P content of 5.9% in BC derived from swine solids (Cantrell et al., 2012), 2.96% in BC produced from chicken manure (Xiao et al., 2018), and 2.57% in BC derived from poultry manure (Brantley et al. 2016). Similar results were obtained for K content, which depends on biomass type and pyrolysis temperature, and the high K content was explained by to the concentration impact. For K content in BC produced from poultry manure increased from 3.88 to 5.88% when the heating temperature was increased from 400 to 600°C (Subedi et al. 2016). In their study, Vaughn et al. (2018) reported K values of 3.89, 3.98, 4.06, 4.02, 8.12, and 9.83 in biosolid-derived BC heated at 300, 400, 500, 700, and 900°C, respectively.

The current investigation explored the impact of the pyrolysis temperature used to create BC generated from palm tree fronds, a common agricultural waste in Upper Egypt, the BC addition rate, and their interaction. The aim of the study was to apply BC as a natural agricultural improvement in order to modify some undesirable soil chemical properties and evaluate the influence on germination parameters of barley seedlings grown under problematic conditions. The results clearly indicate that PT₇₀₀ had the most influence on most of the studied soil parameters (ECe, CaCO₃, SOM, and CEC), and had a profound effect on improving the availability of macro- and micronutrients, except AvMn in the first season. PT₃₅₀ was found to have the most impact on soil pH. In addition, BC-amended soil, regardless of the application rate, showed the best values compared with un-amended soil (BC₀). Regarding the potential effect on germination parameters of barley seeds grown under problematic conditions, we found that the highest values were obtained for PT₃₅₀ and PT₇₀₀ (as an individual influence of pyrolysis temperature) and BC₁ and BC₂ (as an individual effect of BC addition rate).

Acknowledgement: Not applicable.

Author contribution: AAMA; Conceptualization, data curation, methodology, writing and Visualization; MAO; data collection, resources, methodology and formal analysis; AG; investigation, methodology and resources, AA; writing—review and editing. All authors contributed to the study conception and design.

Funding: Open access funding provided by the Science, Technology and Innovation Funding Authority (STDF) in cooperation with the Egyptian Knowledge Bank (EKB).

Data Availability Statement: The data presented in this study are available upon request from the corresponding author.

Ethics statement: Identifies Aswan University that approved the collection of plant or seed specimens and confirms that all methods were carried out in accordance with relevant guidelines and regulations.

Conflict of Interest: The authors declare that they have no conflict of interests concerning the current research publication.

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Table 1. Average monthly climatic data for Aswan region in Egypt in 2020/2021 and 2021/2022 seasons.

Month	° C		(%)	(ms^-1)	(mm d^-1)	(mm d^-1)
Month	ADT	ANT	ARH	AWS	AM-APC-A	AP
2020/2021 season
November	10.37	32.81	35.50	2.82	2.53	0.00
December	4.76	25.77	46.69	2.87	2.85	0.00
January	1.90	25.23	50.75	3.20	2.89	0.00
February	2.88	28.19	42.50	3.21	2.67	0.02
2021/2022 season
November	7.77	28.27	45.75	3.09	2.90	0.00
December	7.60	30.08	39.25	2.46	2.91	0.00
January	4.36	29.26	38.81	2.81	2.78	0.00
February	2.26	28.47	36.44	3.50	3.21	0.00

ADT, average day temperature; ANT, average night temperature; ARH, average relative humidity; AWS, average wind speed; AP, average precipitation.

Table 2. Details of treatments applied in this study.

PT	BC rate	Interactions	Composition	Replication
PT₃₅₀	BC₀	PT₃₅₀x BC₀	Un-amended soil (No BC applied)	These treatments were applied in six replicates
	BC₁	PT₃₅₀x BC₁	applying of PTF-derived BC pyrolysis at 350 °C with rate at 28.0 g.pot⁻¹
	BC₂	PT₃₅₀x BC₂	applying of PTF-derived BC pyrolysis at 350 °C with rate at 56.0 g.pot⁻¹
PT₅₀₀	BC₀	PT₅₀₀x BC₀	Un-amended soil (No BC applied)
	BC₁	PT₅₀₀x BC₁	applying of PTF-derived BC pyrolysis at 500 °C with rate at 28 g.pot⁻¹
	BC₂	PT₅₀₀x BC₂	applying of PTF-derived BC pyrolysis at 500 °C with rate at 56.0 g.pot⁻¹
PT₇₀₀	BC₀	PT₇₀₀x BC₀	Un-amended soil (No BC applied)
	BC₁	PT₇₀₀x BC₁	applying of PTF-derived BC pyrolysis at 700 °C with rate at 28.0 g.pot⁻¹
	BC₂	PT₇₀₀x BC₂	applying of PTF-derived BC pyrolysis at 700 °C with rate at 56.0 g.pot⁻¹

PT₃₅₀, PT₅₀₀, and PT₇₀₀ represent pyrolysis temperature of 350, 500, and 700 °C, respectively. BC₀, BC₁, and BC₂ represent BC addition at 0.0, 28.0, and 56.0 g.pot, respectively. PTF-BC, palm-tree-frond-derived biochar.

Table 3. Some soil chemical and physical properties.

Soil property	2020/2021 season	2021/2022 season
Particle size distribution (%)
Sand	80.45	81.40
Silt	11.30	10.50
Clay	7.25	8..10
Soil texture	Loamy sand	Loamy sandy
pH (in soil paste)	8.15	8.13
ECe (dS.m⁻¹)	10.8	10.7
SOM (%)	1.63	1.70
CaCO₃ (%)	19.1	18.8
CEC (Cmol₊kg⁻¹)	7.20	7.20
Soluble ions (mmol L^-1)
CO₃^--	----	----
HCO₃^-	12.8	13.7
Cl^-	63.4	65.3
SO₄^--	19.3	31.1
Ca⁺⁺	39.6	41.2
Mg⁺⁺	17.8	18.4
Na⁺	22.4	24.3
K⁺	25.7	26.2
Macronutrients (mg.kg⁻¹)
Total N	7.01	7.05
Available P (extractable with NaHCO₃ pH=8.5)	3.57	3.58
Available K (extractable with NH₄OAC pH=7.0)	67.1	67.4
DTPA Extractible micronutriments (mg.kg⁻¹)
Fe	9.7	10.2
Mn	14.5	16.3
Zn	0.15	0.14
Cu	0.48	0.38

Table 4. Effect of different pyrolysis temperatures (PTs) on elemental composition and atomic ratios of palm tree fronds-derived biochar (PTF-BC) samples.

Parameters	Pyrolysis temperature ( °C)
Parameters	PT₃₅₀	PT₅₀₀	PT₇₀₀
pH*	9.15	9.76	11.68
ECe (dS.m⁻¹)**	11.70	8.52	7.70
CEC (cmol.kg⁻¹)	44.89	45.72	47.15
Elemental composition (%, on basis oven-dry weight)
C	57.77	58.45	63.14
O	15.40	10.10	7.30
N	2.20	2.80	4.20
P	0.106	0.113	0.164
K	2.24	1.98	0.82
Ca	0.65	2.24	2.81
Mg	0.17	0.54	0.58
Si	0.69	0.34	0.49
Cl	1.04	1.20	0.62
Molar ratio
O/C	0.1999	0.1296	0.0866
(O+N)/C	0.2272	0.1622	0.1323

PT₃₅₀, PT₅₀₀ and PT₇₀₀ represent pyrolysis temperature (PT) of palm fronds at 350, 500 and 700 °C, respectively.

Table 5. Impact of pyrolysis temperatures (PTs) of palm-tree-frond-derived BC on chemical properties of sandy loam clay soil with undesirable characteristics (ECe=10.8 vs. 10.7 dS.m⁻¹, CaCO₃=19.1 vs. 18.8% and soil pH = 8.15 vs. 8.13) in 2020/2021 and 2021/2022 seasons, respectively.

SCP	Soil pH	ECe	CaCO₃	SOM	CEC
Unit	Soil pH	(dS.m⁻¹)	(%)		(Cmol.kg⁻¹)
2020/2021 season
PT₃₅₀	8.14c±0.07	10.38a±0.95	18.86a±1.57	1.37c±0.15	7.26c±1.51
PT₅₀₀	8.24b±0.07	7.27b±1.05	14.95b±2.18	1.71b±0.16	11.06b±1.54
PT₇₀₀	8.36a±0.06	6.00c±1.91	11.79c±2.42	1.89a±0.15	12.56a±1.77
LSD_0.05	**	**	**	**	**
2021/2022 season
PT₃₅₀	8.12c±0.08	10.32a±0.65	18.85a±1.51	1.51c±0.13	7.37c±1.40
PT₅₀₀	8.23b±0.06	7.58b±1.02	15.17b±2.20	1.78b±0.16	11.12b±1.52
PT₇₀₀	8.35a±0.08	6.22c±1.95	11.86c±2.40	1.94a±0.09	12.53a±1.70
LSD_0.05	**	**	**	**	**

Means followed by same letter in each column indicate non-significant differences (p ≤ 0.05). Ece, electrical conductivity; CaCO₃, calcium carbonate; SOM, soil organic matter; CEC, cation exchange capacity. PT₃₅₀, PT₅₀₀, and PT₇₀₀ represent pyrolysis temperature of 350, 500, and 700 °C, respectively.

Table 6. Impact of pyrolysis temperatures (PTs) of palm-tree-frond-derived BC on available macro- and micronutrients of sandy loam clay soil with undesirable characteristics (ECe=10.8 vs. 10.7 dS.m⁻¹, CaCO₃=19.1 vs. 18.8% and soil pH = 8.15 vs. 8.13) in 2020/2021 and 2021/2022 seasons, respectively.

Treatment	NH₄⁺-N	AvP	AvK	AvFe	AvMn	AvZn
Treatment	(mg.kg⁻¹)			(mg.kg⁻¹)
2020/2021 season
PT₃₅₀	4.73c±1.09	5.46a±2.02	108.00b±1.09	2.88b±1.93	1.65a±2.19	1.30a±1.09
PT₅₀₀	7.67b±1.11	5.49a±2.87	118.89a±1.73	3.28ab±1.09	1.60a±2.98	1.22b±1.09
PT₇₀₀	12.45a±2.01	6.02a±1.03	112.67ab±1.92	3.52a±1.93	1.58a±2.01	1.32a±1.28
2021/2022 season
PT₃₅₀	5.06c±1.73	8.58c±2.07	260.67b±2.98	3.18b±1.94	1.33a±2.35	1.58a±1.98
PT₅₀₀	9.34b±1.04	9.60b±1.30	279.11b±2.01	3.68a±1.09	1.35a±2.94	1.57a±1.28
PT₇₀₀	11.68a±1.03	10.92a±2.01	312.67a±1.02	3.70a±1.45	1.42a±1.93	1.67a±1.73

Means followed by same letter in each column indicate non-significant differences (p ≤ 0.05). NH₄⁺-N, ammonium nitrogen; AvP, AvK, AvFe, AvMn, and AvZn represent available phosphorus, potassium, iron, manganese, and zinc, respectively. PT₃₅₀, PT₅₀₀ and PT₇₀₀ represent pyrolysis temperature of 350, 500 and 700 °C, respectively.

Table 7. Impact of addition rate of palm-tree-frond-derived biochar (BC) on chemical properties of sandy loam clay soil with undesirable characteristics (ECe=10.8 vs. 10.7 dS.m⁻¹, CaCO₃=19.1 vs. 18.8% and soil pH = 8.15 vs. 8.13) in 2020/2021 and 2021/2022 seasons, respectively.

SCP	Soil pH	ECe	CaCO₃	SOM	CEC
Unit	Soil pH	(dS.m⁻¹)	(%)		(Cmol.kg⁻¹)
2020/2021 season
BC₀	8.25a±0.01	8.75a±0.09	16.01a±0.10	1.67a±0.03	10.15b±0.02
BC₁	8.23a±0.01	8.32a±0.83	15.34b±0.75	1.61a±0.01	10.25b±0.06
BC₂	8.24a±0.01	6.57b±1.10	14.25a±0.83	1.69a±0.03	10.49a±0.33
LSD_0.05	ns	**	**	ns	*
2021/2022 season
BC₀	8.24a±0.01	9.01a±0.15	16.14a±0.09	1.71a±0.06	10.25b±0.07
BC₁	8.24a±0.02	8.15b±0.70	15.36a±0.82	1.72a±0.03	10.27b±0.06
BC₂	8.21a±0.01	6.96c±1.20	14.40a±0.83	1.80a±0.03	10.50a±0.26
LSD_0.05	ns	**	**	ns	**

Means followed by same letter in each column indicate non-significant difference (P ≤ 0.05). Soil pH indicates soil reactivity. EC, electrical conductivity; CaCO₃, calcium carbonate; SOM, soil organic matter, CEC, cation exchange capacity. BC₀, BC₁, and BC₂ represent BC addition rate of 0, 28, and 56, respectively.

Table 8. Impact of addition rate of palm-tree-frond-derived biochar (BC) on available of macro and micronutrients of sandy loam clay soil with undesirable characteristics (ECe=10.8 vs. 10.7 dS.m⁻¹, CaCO₃=19.1 vs. 18.8% and soil pH = 8.15 vs. 8.13) in 2020/2021 and 2021/2022 seasons, respectively.

Treatment	NH₄⁺-N	AvP	AvK	AvFe	AvMn	AvZn
Treatment	(mg.kg⁻¹)			(mg.kg⁻¹)
2020/2021 season
BC₀	7.45a±	5.64a±	112.89a±	3.12a±	1.64a±	1.25a±
BC₁	8.95a±	5.66a±	111.56a±	3.23a±	1.53a±	1.30a±
BC₂	8.45a±	5.67a±	115.11a±	3.33a±	1.65a±	1.28a±
2021/2022 season
BC₀	7.40b±	9.63a±	279.56b±	3.60a±	1.37ab±	1.62a±
BC₁	8.95a±	9.69a±	284.89ab±	3.52a±	1.30b±	1.63a±
BC₂	9.73a±	9.77a±	288.00a±	3.43a±	1.43a±	1.57a±

Means followed by the same letter in each column mean are not significant difference (at P ≤ 0.05). Soil pH=soil reactivity, EC=Soil electrical conductivity, CaCO₃=calcium carbonate, SOM=soil organic matter, CEC=cation exchange capacity. BC₀, BC₁ and BC₂ represent addition rate of palm fronds-derived BC at 0, 28 and 56, respectively.

Table 9. Impact of interaction between pyrolysis temperature (PT), and biochar (BC) addition rate on some chemical properties of sandy loam clay soil with undesirable characteristics (ECe=10.8 vs. 10.7 dS.m⁻¹, CaCO₃=19.1 vs. 18.8% and soil pH = 8.15 vs. 8.13) in 2020/2021 and 2021/2022 seasons, respectively.

Treatment	Soil pH	ECe	CaCO₃	SOM	CEC
Treatment		(dS.m⁻¹)	(%)		(Cmol.kg⁻¹)
Pyrolysis temperature (PT) x biochar addition rate (BC)
2020/2021 season
PT₃₅₀ x BC₀	8.13d±0.02	10.55a±0.17	18.77b±0.16	1.40d±0.06	7.23d±0.17
PT₃₅₀ x BC₁	8.15d±0.02	10.35a±0.23	19.06a±0.09	1.30d±0.06	7.27d±0.07
PT₃₅₀ x BC₂	8.15d±0.01	10.24a±0.26	18.77b±0.58	1.40d±0.12	7.28d±0.14
PT₅₀₀ x BC₀	8.26b±0.01	8.36b±0.33	15.94c±0.60	1.67c±0.09	10.96c±0.13
PT₅₀₀ x BC₁	8.22c±0.01	7.79bc±0.25	15.43d±0.13	1.70bc±0.06	11.05c±0.07
PT₅₀₀ x BC₂	8,24bc±0.02	5.65e±0.23	13.48e±0.62	1.77a-c±0.12	11.18c±0.05
PT₇₀₀ x BC₀	8.36a±0.01	7.34cd±0.58	13.33e±0.64	1.93a±0.09	12.26b±0.19
PT₇₀₀ x BC₁	8.37a±0.01	6.84d±0.45	11.52f±0.13	1.83a-c±0.09	12.43b±0.06
PT₇₀₀ x BC₂	8.36a±0.02	3.83f±0.14	10.51g±0.58	1.90ab±0.06	13.00a±0.86
2021/2022 season
PT₃₅₀ x BC₀	8.13c±0.01	10.25a±0.38	18.70a±0.58	1.47d±0.09	7.51e±0.05
PT₃₅₀ x BC₁	8.13c±0.02	10.10a±0.27	18.99a±0.07	1.43d±0.03	7.34e±0.14
PT₃₅₀ x BC₂	8.09c±0.05	10.62a±0.55	18.91a±0.22	1.63cd±0.03	7.26e±0.12
PT₅₀₀ x BC₀	8.24b±0.03	8.75b±0.37	16.23b±0.07	1.77bc±0.03	11.10d±0.10
PT₅₀₀ x BC₁	8.22b±0.01	7.68c±0.35	15.72c±0.14	1.73a-c±0.09	11.01d±0.07
PT₅₀₀ x BC₂	8.21b±0.01	6.32d±0.35	13.55d±0.19	1.83a-c±0.09	11.24d±0.13
PT₇₀₀ x BC₀	8.35a±0.04	8.04bc±0.27	13.48d±0.13	1.90ab±0.01	12.14c±0.01
PT₇₀₀ x BC₁	8.35a±0.01	6.66d±0.22	11.38e±0.19	2.00a±0.01	12.43b±0.02
PT₇₀₀ x BC₂	8.35a±0.01	3.95e±0.13	10.72f±0.14	1.93ab±0.09	13.01a±0.01

Means followed by the same letter in each column mean are not significant difference (at p ≤ 0.05). EC = Soil electrical conductivity, CaCO₃ = calcium carbonate, SOM = soil organic matter, CEC = cation exchange capacity. PT₃₅₀, PT₅₀₀ and PT₇₀₀ represent pyrolysis temperature at 350, 500 and 700 °C. BC₀, BC₁ and BC₂ represent addition rate of palm fronds-derived biochar at 0, 28 and 56 g.pot⁻¹, respectively.

Table 10. Impact of interaction between pyrolysis temperature (PT) and biochar (BC) addition rate on available macro and micronutrients of sandy loam clay soil with undesirable characteristics (ECe=10.8 vs. 10.7 dS.m⁻¹, CaCO₃=19.1 vs. 18.8% and soil pH = 8.15 vs. 8.13) in 2020/2021 and 2021/2022 seasons, respectively.

Treatment	NH₄⁺-N	AvP	AvK	AvFe	AvMn	AvZn
Treatment	(mg.kg^⁻1)
2020/2021 season
PT₃₅₀ x BC₀	3.50d±0.44	6.41c±0.46	220.67c±2.40	2.80cd±1.09	1.70ab±1.11	1.30ab±1.07
PT₃₅₀ x BC₁	3.50d±0.34	7.00bc±0.34	218.67c±3.46	2.70d±0.93	1.65ab±1.92	1.25ab±2.94
PT₃₅₀ x BC₂	3.50d±1.17	7.10bc±0.42	209.33c±4.84	3.15b-d±0.91	1.60ab±1.30	1.35ab±2.01
PT₅₀₀ x BC₀	7.01c±0.58	7.74a-c±0.37	246.67b±1.76	3.30a-d±1.93	1.78a±1.03	1.25ab±2.95
PT₅₀₀ x BC₁	9.34b±0.93	7.74a-c±0.14	258.00ab±6.77	3.10b-d±1.09	1.45b±1.03	1.25ab±2.06
PT₅₀₀ x BC₂	8.18bc±0.33	7.76a-c±0.08	256.00ab±4.06	3.45ab±1.27	1.55ab±1.96	1.15b±2.49
PT₇₀₀ x BC₀	9.34b±0.29	8.35ab±0.28	270.00a±4.10	3.25b-d±1.95	1.45b±1.95	1.20ab±1.93
PT₇₀₀ x BC₁	12.84a±0.73	8.02ab±0.11	276.67a±7.57	3.90a±1.03	1.59b±1.20	1.40a±1.04
PT₇₀₀ x BC₂	14.01a±1.15	8.96a±0.24	272.67a±4.16	3.40a-c±1.04	1.80a±0.99	1.35ab±1.07
2021/2022 season
PT₃₅₀ x BC₀	4.65e±1.17	8.37c±0.14	253.33d±2.40	3.50a-c±1.17	1.25c±0.14	1.75ab±2.40
PT₃₅₀ x BC₁	4.84de±1.14	8.66c±0.14	264.67cd±6.36	3.15cd±1.14	1.30bc±0.14	1.60bc±6.36
PT₃₅₀ x BC₂	4.69e±1.16	8.70c±0.22	264.00cd±4.62	2.85d±1.16	1.45ab±0.22	1.40c±4.62
PT₅₀₀ x BC₀	8.17cd±1.15	9.61b±0.18	274.67bc±4.82	3.91a±1.15	1.35a-c±0.18	1.70ab±4.82
PT₅₀₀ x BC₁	9.34bc±1.17	9.35b±0.26	282.67b±5.96	3.55a-c±1.17	1.30bc±0.26	1.60bc±5.96
PT₅₀₀ x BC₂	10.51bc±1.01	9.83b±0.05	280.00b±7.02	3.60a-c±1.01	1.40a-c±0.05	1.40c±7.02
PT₇₀₀ x BC₀	9.34bc±1.17	10.93a±0.33	310.67a±4.06	3.40bc±1.17	1.50a±0.33	1.40c±4.06
PT₇₀₀ x BC₁	11.68ab±1.15	11.05a±0.08	316.67a±2.91	3.85ab±1.15	1.30bc±0.08	1.70ab±2.91
PT₇₀₀ x BC₂	13.95a±1.03	10.78a±0.09	310.67a±1.33	3.85ab±1.03	1.45ab±0.09	1.90a±1.33

Table 11. Impact of interaction between pyrolysis temperature (PT) and biochar (BC) addition rate on some germination parameters (GP) of barley seeds grown in sandy loam clay soil with undesirable characteristics (ECe=10.8 vs. 10.7 dS.m⁻¹, CaCO₃=19.1 vs. 18.8% and soil pH = 8.15 vs. 8.13) in 2020/2021 and 2021/2022 seasons, respectively.

GP	GP	GR	SV	MET
GP	(%)		SV	day
2020/2021 season
PT₃₅₀ x BC₀	73.36b±	22.72c±	2875.56b±	0.41a-c±
PT₃₅₀ x BC₁	66.67c±	22.58c±	1264.44e±	0.37b-d±
PT₃₅₀ x BC₂	66.67c±	16.94e±	2062.22c±	0.37b-d±
PT₅₀₀ x BC₀	37.78f±	37.30b±	866.67f±	0.21e±
PT₅₀₀ x BC₁	60.00d±	14.54e±	1653.33d±	0.33cd±
PT₅₀₀ x BC₂	75.56b±	14.90e±	3040.00b±	0.42ab±
PT₇₀₀ x BC₀	24.45g±	58.33a±	453.33g±	0.14f±
PT₇₀₀ x BC₁	52.22e±	7.50f±	1297.78e±	0.31d±
PT₇₀₀ x BC₂	84.44a±	19.74d±	3900.00a±	0.47a±
LSD_0.05	**	**	**	**
2021-2022 season
PT₃₅₀ x BC₀	31.11d±	24.21b±	508.84f±	0.17bc±
PT₃₅₀ x BC₁	51.11c±	18.41de±	1010.89e±	0.28a-c±
PT₃₅₀ x BC₂	57.78bc±	22.54bc±	1884.44c±	0.32a-c±
PT₅₀₀ x BC₀	24.44d±	15.28e±	478.89f±	0.14c±
PT₅₀₀ x BC₁	57.78bc±	33.33a±	1271.11d±	0.32a-c±
PT₅₀₀ x BC₂	64.44b±	21.30b-d±	3128.89a±	0.36ab±
PT₇₀₀ x BC₀	24.44b±	19.44cd±	597.78f±	0.21a-c±
PT₇₀₀ x BC₁	63.78b±	17.84de±	1691.11c±	0.36ab±
PT₇₀₀ x BC₂	75.56a±	17.88de±	2700.00b±	0.42a±
LSD_0.05	**	**	**	**

Means followed by the same letter in each column mean are not significant difference (at p ≤ 0.05). GP = germination percentage; GR = germination rate; SV = seed vigor; and MET = mean emergence time. PT₃₅₀, PT₅₅₀ and PT₇₀₀ represent pyrolysis temperature (PT) at 350, 550 and 700 °C. BC₀; BC₁ and BC₂ represent of palm tree fronds-biochar (PTF-BC) represent BC at 0.0, 28.0 and 56.0 g.pot⁻¹, respectively.

No competing interests reported.

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Biochar: A Surrogate Approach to Modulating Soil Chemical Properties and Germination Parameters of Barley Plants Grown under Multi-Stress Conditions

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