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Sustainable Soil Management in Alkaline Soils: The Role of Biochar and Organic Nitrogen in Enhancing Soil Fertility

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14 October 2024

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15 October 2024

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Abstract
Biochar (BC) serves a vital function in sequestering carbon, improving nutrient cycles, and boosting overall soil quality. This research investigated how both biochar and nitrogen, derived from both organic and inorganic sources, influence the physical and chemical properties of alkaline soils in semi-arid regions. The study particularly emphasized the effects on nitrogen availability. A field experiment was carried out from 2015 to 2017 using a randomized complete block design (RCBD) with a split-plot arrangement. The study involved applying biochar at various rates (0, 10, 20, and 30 t ha⁻¹) and nitrogen at different levels (0, 90, 120, and 150 kg ha⁻¹) using urea, farmyard manure (FYM), and poultry manure (PM) as nitrogen sources. The application of biochar at the highest rate (30 t ha⁻¹) significantly increased soil organic carbon (SOC), soil organic matter (SOM), and soil moisture content (SMC) by over 120%. Additionally, it led to increases in total soil nitrogen (STN) by 14.16% and mineral nitrogen (SMN) by 9.09%. Conversely, biochar applications at this rate decreased soil bulk density (SBD), pH, and electrical conductivity (EC) by 28.52%, 3.38%, and 2.27%, respectively, compared to the control group. Similarly, applying nitrogen at 150 kg ha⁻¹ using FYM significantly improved SOC, SOM, SMC, and SBD. Using PM as a nitrogen source at the same rate enhanced STN and SMN while lowering soil pH and EC. In conclusion, the study demonstrated that combining biochar at a rate of 30 t ha⁻¹ with nitrogen at 150 t ha⁻¹, derived from either PM or FYM, holds significant promise for enhancing soil fertility and promoting carbon sequestration in alkaline soils within semi-arid environments. These findings underscore the value of integrating BC and organic N sources to enhance agroecosystem sustainability. Thus, the study provides a promising pathway to enhance soil quality, improve crop productivity, and support sustainable agricultural practices in challenging environments.
Keywords: 
Subject: Biology and Life Sciences  -   Agricultural Science and Agronomy

1. Introduction

Inorganic fertilizer application is widely regarded as the most effective technique for improving soil fertility among various agricultural practices [1]. Nevertheless, the persistent use of inorganic fertilizers has led to significant negative impacts on the soil's physical and chemical characteristics, including the reduction of soil organic matter (SOM) [2]. Harmful factors associated with the use of conventional fertilizers include prolific leaching of nutrients into groundwater and eutrophication, significant fossil fuel consumption during fertilizers production, and the ever-increasing costs associated with these fertilizers [3]. Consequently, there would be strong support for fertilization methods that are both efficient and eco-friendly. Organic fertilizers, which are a rich source of nutrients, are generally derived from animal manure and poultry droppings etc. [4]. It has been revealed that organic manure can alter soil’s physical and chemical properties due to their comprehensive nutrient content [5]. Furthermore, the fertilizer efficiency of organic manures is long-term compared to mineral fertilizers [6]. Consequently, utilizing organic manure represents an ideal method for recycling nutrients in the soil and minimizing environmental contamination [7]. However, the nutrient release from organic manures is generally slow and unpredictable, which limits their widespread use [8]. Additionally, the benefits of organic manure are often short lived in soil due to the rapid degradation of soil organic matter under high temperatures [9]. Therefore, the additional organic matter is generally mineralized within a few days after application [10].
Hence, there is a need to explore alternative means of sustainable soil management to boost the current yield potential of soils. Sustainable management of soil requires techniques that maintain and improve soil physical and chemical properties while ensuring optimal crop yield over time. Therefore, to maintain soil fertility, there is an urgent need to use highly stable and nutrient retentive organic materials such as biochar (BC) [11]. BC is a porous, carbon-based material derived from the thermal decomposition of organic matter in low-oxygen conditions. Its unique physico-chemical characteristics make it well-suited for long-term carbon storage in the environment and offer promising potential for enhancing soil properties [12]. The use of biochar for soil improvement is receiving growing interest because of its ability to enhance soil health, increase crop productivity, and sequester carbon [13]. The addition of BC can increase soil water availability [14], water holding capacity [15], soil aeration [16], soil organic carbon (SOC) content [17], soil microbial activity as well as biomass [18], enzyme activity [19], and nutrient retention and availability [20], resulting in reduced fertilizer requirements and decreased nutrient leaching [21]. Previous studies have shown that BC can improve soil nutrient concentration, cation exchange capacity, soil structure, and nutrient use efficiency, while also reducing soil acidity [22]. It has been demonstrated that the application of BC alters N dynamics within the soil [23]. Due to its high adsorption capacity, BC effectively retains nitrate and ammonium, making it beneficial for both water treatment and soil applications [24], This characteristic allows for enhanced storage of ammonium-N in the soil [25]. To address the issue of potentially inaccessible nitrogen, research has shown that combining BC with N fertilizer can yield positive results by enhancing the efficiency of mineral nitrogen fertilizers, decreasing the reliance on inorganic fertilizers, and reducing costs [26]. Research has shown that incorporating biochar made from materials like wood, maize straw, and rice husks can lead to notable increases in soil nitrogen content. For instance, a study by Varela Milla et al. [27], found that after two years, this practice increased STN by 63% and SMN by 40%. Similarly, Wu et al. [28] noted improvements in STN production following the application of wood biochar. Additionally, Major et al. [29] found that the incorporation of wood biochar could either raise or lower soil pH, depending on the type of feedstock used for biochar production and the specific soil type. Wood biochar typically has a much lower bulk density (BD) compared to that of the soil, resulting in a decrease in soil BD upon its incorporation [30]. The presence of plant nutrients and ash in biochar, combined with its high surface area, porous structure, and ability to provide a habitat for microorganisms, has been identified as crucial in enhancing soil properties and improving nutrient uptake by plants in biochar-amended soils [31].
This study hypothesized that the combined application of BC and N from organic sources, such as farmyard manure and poultry manure, would significantly enhance soil physico-chemical properties, including organic matter, nitrogen availability, and soil structure, compared to the application of either biochar or nitrogen alone in alkaline soils under a semi-arid environment. The main objective of this study was to assess the combined effects of biochar and nitrogen from different organic and inorganic sources on key soil health indicators over a two-year period. Additionally, the study aimed to assess the carryover effects of biochar on soil properties and nitrogen dynamics beyond the initial application period.

2. Materials and Methods

2.1. Experimental Site Description and Treatments

A field trial was performed at the Agriculture Research Station in Swabi, Khyber Pakhtunkhwa, Pakistan, during the autumn seasons of 2015 and 2017. The study area is located between the coordinates 34° 7' 48" N and 72° 28' 11" E, situated between the Indus River and the Kabul River in Khyber Pakhtunkhwa Province, Pakistan. The total monthly rain fall was 0 - 188 mm while mean monthly air temperature was 11.89 oC to 34.68 oC during the experiment. The soil of the experimental site belongs to Gulyana soil series. The experimental field had previously been under wheat (Triticum avestum L.) and maize (Zea mays L.) cropping system.
During both years, the experiment involved four wood biochar (BC) application rates (0, 10, 20, and 30 t ha⁻¹) and three nitrogen (N) management levels (90, 120, and 150 kg ha⁻¹), with a control treatment included. The nitrogen needed was supplied from urea, farmyard manure (FYM), and poultry manure (PM). A randomized complete block design with factorial arrangements was used to apply the ten treatments (Control, 90 kg ha-1 N Urea, 120 kg ha-1 N Urea, 150 kg ha-1 Urea, 90 kg ha-1 N, FYM, 120 kg ha-1 N FYM, 150 kg ha-1 N FYM, 90 kg ha-1 N PM, 120 kg ha-1 N PM and 150 kg ha-1 N PM). The treatments were repeated three times. Each main plot was comprised of 10 sub-plots and each sub-plot was 3 × 4 m2. The distance between the main plots was 1 m while sub-plots were 0.5 m apart. The same field and layout of the experiment were maintained for the experiment in 2016-17.

2.2. Application of Biochar, Urea, FYM, PM and Sowing of Wheat Seeds

Biochar produced from the prunings of Acacia trees was sourced from the Malakandher Research Farm at The University of Agriculture Peshawar, Pakistan. The detailed production procedure is already given by [32]. The FYM and PM were collected from the dairy and poultry farms of the local farmer. The manures were kept under cover for 3 weeks before they were used in the field experiments.
After land preparation, the experimental field was laid out to the required plot size of 3 × 4 m2. The biochar (BC) was sieved through a 2 mm mesh, weighed and applied to main plots according to the required rates. Moreover, the BC was mixed in the soil to a depth of 15 cm with the help of rotavator. The exact nitrogen content in FYM and PM was determined through laboratory analysis and then meticulously incorporated into the sub-plots by hoeing, ensuring no cross-contamination with adjacent sub-plots. The nitrogen content from urea was accurately calculated using the 46% listed on the packaging and applied in two separate doses: one half at the time of sowing and the other half during the tillering stage. Additionally, FYM and PM were incorporated into the soil one week before sowing, while BC was applied during seedbed preparation. BC was applied once, while urea, FYM and PM were applied during both seasons. All sub-plots received a basal dose of 90 kg ha⁻1of phosphorus (P) and 60 kg ha⁻1 of potassium (K), delivered in the form of potassium sulfate for K and single super phosphate for P.Wheat seeds sowing was done on November 8th, 2015, and November 5th, 2016. Wheat variety (Pirsabaq-2013) was used as a test crop. The Cereal Crops Research Institute (CCRI) in Pirsabak Nowshera, Pakistan is the source of the cultivar. A seed rate of 120 kg ha⁻¹ was applied in 3 x 4 m2 plots, maintaining a row spacing of 30 cm. Sowing was carried out using a hand hoe. Broad spectrum herbicide ‘Atlantus’ was used to control weeds in wheat crops. Crops were irrigated as needed using canal water. Normal cultural practices were carried out throughout the growing period of the crop.

2.3. Determination of the Post-Harvest, Soil Physico-Chemical Properties

Before the start of the experiment in 2015, surface soil samples from 0 to 15 cm depth were indiscriminately obtained from various locations of the experimental site with the help of soil auger. The obtained soil samples were bulked dried and passed through a 2 mm sieve and examined for numerous soil physico-chemical properties. Data regarding various soil parameters at pre-sowing stage are already published in Khan et al. [4]. Moreover, soil samples were also taken after harvest of wheat in both years (2015 and 2017), from each sub-plot, and were examined for soil physico-chemical properties. For soil moisture at harvest the soil sample was collected and put in moisture cane and weight, and was dried at 105ºC, further calculations were done using the formula of Reeb [33]. Soil BD was determined using the procedure outlined by Blake et al. [34]. SOC was calculated by the method of Walkley and Black via the dichromate wet oxidation method [35]. Soil OM was sorted by multiplying C content by factor 1.724. The pH and electrical conductivity (EC) of the soil were measured using the methods detailed by McLean [36] and Rhoades [37]. In this method, a 1:5 soil-to-water suspension was analyzed for pH and electrical conductivity (EC) using a pH meter and an EC meter, respectively. Total soil nitrogen (STN) was determined calorimetrically for each treatment, following the Kjeldahl procedure outlined by Bremner et al. [38]. For the determination of SMN, steam distillation procedure as described by [39] was used.

2.4. Composition of Biochar, FYM and PM

In this study, biochar (BC) was generated from the prunings of Acacia trees. In FYM and PM, the concentrations of nitrogen, phosphorus, and potassium were 0.87%, 0.34%, and 0.6%, respectively. The experiment's biochar has 0.08% nitrogen and 0.112% phosphorus in it [4].

2.5. Statistical Analysis

Data collected from each year, as well as the combined data, were statistically analyzed using SPSS version 20, following a two-factorial randomized complete block design. Additionally, the means were compared using the least significant difference (LSD) test at a 5% significance level [40].

3. Results

3.1. Effect of Biochar and N Management on Soil Physical Properties

The effect of the applications of biochar (BC) and N management on soil physical properties are presented in Table 1. Across both years, and when considered as individual factors, the application of BC significantly (p < 0.05) influenced soil physical properties. Lower bulk density (BD) and greater moisture content were recorded compared to the control. BC reduced bulk density and increased moisture content as the levels of the BC increased and BC applied at 30 t ha−1 resulted in least BD and higher moisture content. Combined data over the two years showed that BC applied at 10, 20, and 30 t ha−1 reduced BD by 2.30%, 18.27%, and 39.90%, and increased moisture content by 27.58%, 47.80%, and 121.30%, respectively, compared to the control (Table 1).
Similarly, N management in both years and as individual factor also significantly improved soil physical properties compared with the control. Reduced BD and increased SMC were noted when compared with the control. Generally, N management reduced soil BD and increased SMC as N levels increased, with the addition of 150 kg N ha⁻¹ from organic sources resulting in the lowest BD and the highest SMC. Specifically, applying 150 kg N ha⁻¹ exclusively from organic sources, such as FYM, led to a 20.48% reduction in BD. Additionally, this application increased SMC by 78.29% compared to the N control treatment. In general, the interaction of BC × N showed that soil moisture content (SMC) improved as the levels of biochar (BC) and nitrogen (N) increased from 0 to 30 t ha⁻¹ of BC and from 0 to 150 kg ha⁻¹ of N. Specifically, the highest SMC of 18.53% was observed with the individual application of 30 t ha⁻¹ BC and 150 kg ha⁻¹ nitrogen N from FYM, compared to other treatments, including the control (Figure 3).

3.2. Effect of Biochar and N Management on Soil Chemical Properties

Table 1 and 2 demonstrate the effect of biochar (BC) and N management on soil chemical properties. In terms of combined effect (both years) and when considered as an individual factor, BC significantly (p < 0.05) improved concentrations of SOC, SOM, STN and SMN when BC applied at 30 t ha−1 and resulted statistically maximum values. Combined over two years data showed that 10, 20 and 30 t ha−1 BC increased SOC by 27.62, 47.86 and 121.38% and SOM by 27.54, 47.76 and 121.24% compared with no application of BC. Moreover, application of 10, 20 and 30 t BC ha−1 also improved STN and SMN by 7.41, 11.03, 14.16, 2.68, 5.91 and 9.09%, respectively over BC control.
Similarly, N management in combined (both years) and as individual factor also considerably improved soil chemical properties when compared to control. SOC, SOM, STN and SMN were enhanced in comparison to the N control. In general, the management of N led to an increase in SOC as N levels rose from 90 to 150 kg N ha⁻¹, regardless of whether the sources were organic or inorganic. Specifically, applying 150 kg N ha⁻¹ from FYM led to increases in SOC and SOM by 78.16% and 78.24%, respectively, in comparison to the N control soil. In terms of STN and SMN, both metrics showed improvement as N levels rose from 90 to 150 kg N ha⁻¹, irrespective of whether the sources were organic or inorganic. In particular, the addition of 150 kg N ha⁻¹ solely from organic sources, such as FYM and PM, led to increases in STN and SMN of 18.37% and 20.88%, respectively, compared to the control. The combined analysis revealed a significant interactive effect of both BC and N management (BC × N) for soil chemical properties. In case of BC × N interaction for SOC, SOM, STN and SMN, highest SOC, SOM were observed where 30 t BC and 150 kg N was applied lonely from FYM (Figure 1 and Figure 2). Whereas the highest STN and SMN were observed where 30 t BC and 150 kg N ha-1 were applied lonely from PM (Figure 4 and 5).
The statistical results showed that the pH values obtained by using biochar (BC) were significantly different (p<0.05) with the results of BC untreated soil (Table 2). Data combined over two years indicated that the addition of 20 t ha⁻¹ of BC considerably reduced soil pH compared to other BC levels and the control soil without BC. In contrast, the pH levels of amended soils with 10 t ha⁻¹ and 30 t ha⁻¹ of BC, as well as the control soil, did not show significant differences.
Similarly, N management also significantly reduce soil pH compared with the control soil. Soil pH generally decreased when N levels were raised from 90 to 150 kg N ha⁻¹, regardless of whether the N came from organic or inorganic sources. However, the application of 150 kg N ha⁻¹ solely from PM significantly lowered soil pH compared to other N levels and the control soil. The highest pH levels were recorded in the control soil and in soils fertilized with 90 kg N ha⁻¹ solely from urea, FYM, and PM. BC × N interaction indicated that, lower soil pH (7.28) was observed where 20 t BC and 150 kg N ha-1 was applied lonely from PM (Figure 6).
The statistical results showed that the application of BC significantly (p<0.05) declined soil EC when compared to BC untreated soil (Table 2). Across years the minimum EC was observed for 30 t BC ha-1 amended soil, while the maximum EC was observed for control soil. Similarly, a combined analysis of variance also revealed significant differences among N management for soil EC. Generally, the soil with controlled N was having the maximum EC followed by soil amended with PM, FYM and Urea. The year effect was also found to be significant with a slight increase of soil EC in the year 2016-17 compared with 2015-16. BC × N interaction indicated that, maximum soil EC (0.240 dS m-1) was recorded where 30 t BC and 90 kg N was lonely applied from urea. However, there were no significant changes among different levels of N applied from organic sources (Figure 7).

4. Discussion

In our study the reduced bulk density (BD) in biochar (BC) amended soil results from the porous nature of BC, which promotes the activity of soil faunas. This increased activity aids in maintaining optimal soil structure, aeration, and water movement due to the higher pore volume, further leading to a reduction in soil BD. Similar findings were reported by Burrell et al. [41]. Furthermore, our findings were supported by the work of Verheijen et al. [42], who reported that BC has a lower BD than soil, thereby leading to a reduction in soil BD. According to our study, the water retained in the pore spaces of the applied BC, which have a high porosity is responsible for the enhancement in SMC. Variations in bulk density among the treatments may explain the differences in SMC observed between the biochar-modified plots and the control. Similar results were observed by Castellini et al. [43], who highlighted that even slight modifications in soil bulk density (SBD) caused by the addition of biochar can significantly influence soil water retention. In a similar vein, Laird et al. [44] reported that biochar amended soil retained 15% more moisture compared to the control soil. Furthermore, biochar's high porosity allows it to retain water in smaller pores, which increases its water-holding capacity and aids in mitigating water stress [45,46].
Soil organic carbon (SOC) is a crucial indicator of soil quality. Our study demonstrated that the increase in SOC may be due to the fused aromatic ring structures in BC, whose high resistance plays a vital role in enhancing C sequestration in the soil. Wang et al. [47] noted that BC is stable in soil and exhibits a slow decomposition rate. Consequently, its high resistance significantly contributes to its effectiveness in improving soil carbon sequestration [48]. The improvement in soil organic matter (SOM) in organic manure-incorporated soil might be due to the increased organic matter content from the incorporation of organic materials. Similar to our results, Bista et al. [49] also observed reduced plant growth in treatments without BC, which led to lower shoot and root biomass and eventually resulted in lower SOM accumulation. Increased SOM in BC amended soil was also observed by Rawat et al. [50]. The increase in soil total nitrogen (STN) in soil amended with biochar (BC) can be connected to the favorable properties of BC, which boosts soil fertility in two significant aspects: it provides essential nutrients such as nitrogen (N), phosphorus (P), and potassium (K), and it effectively retains nutrients (particularly nitrogen) from both organic and inorganic fertilizers, along with those present in the soil. Similar findings were reported by Rawat et al. [50], who noted that biochar facilitates the sustained availability of nutrients such as carbon, nitrogen, potassium, and phosphorus to plants by gradually releasing them after absorption. The study conducted by Kameyama et al. [51] provides additional support for the results of this investigation. They stated that BC has a strong affinity for ammonium (NH₄⁺) and nitrate (NO₃⁻), which helps maximize their retention time in the soil. This potentially leads to improved retention of nitrogen fertilizer in the soil. The addition of biochar modifies the soil's nutritional profile, primarily by enhancing the availability of nutrients that are directly accessible to plants. Consequently, the increase in soil mineral nitrogen (SMN) in biochar amended soils can be attributed to the multifunctional role of biochar. Yuan et al. [52] also reported comparable results. The incorporation of BC into soil results in a reduced rate of mineralization of the BC materials [53]. Various studies have reported differing effects: some observed a decline in net nitrogen (N) mineralization [54], while others noted an enhancement in net N mineralization [54]. Some findings indicated no significant changes in mineralization [55], and others suggested a slight influence on mineralization [56]. Additionally, research by [57] utilized 15N labeling to investigate N dynamics in plots amended with BC and found an increase in N mineralization associated with BC application. In our study the reduction in soil pH might be due to the acidic materials formed from the oxidation and decomposition of BC in the soil. Cheng et al. [58] pointed out that biochar (BC) is not fully inert within the soil; it can oxidize, especially at its surface, due to chemical reactions and the activity of microorganisms. As a result, the generation of acidic functional groups can progressively decrease soil pH by counteracting soil alkalinity. This trend is reinforced by prior studies that indicate a decrease in soil pH after the application of alkaline biochar to the soil [59]. The decline in electrical conductivity (EC) in soil amended with BC could be linked to the reduced ash content present in wood-derived biochar. This result is consistent with Jalal's [60] findings, which showed that EC in plots treated with BC decreased by 20% and 40% after two years. Similarly, Kawsar et al. [61] observed a 20% and 41% decrease in EC in plots that incorporated BC.
The result indicated that SMC was increased in organic manures amended soil. Specifically, highest SMC was observed in FYM amended soil followed by PM amended soil. This can be associated with the enhancement of soil organic matter resulting from manure application. The organic matter present in FYM likely contributed to stabilizing the soil structure, which in turn reduced bulk density and improved SMC. A similar effect of farmyard manure (FYM) on enhancing soil moisture content (SMC) has also been reported by Zhang et al. [62]. Likewise, Singh et al. [63] found that soil moisture levels were higher in plots treated with FYM. Their explanation for this rise was that FYM's colloidal and hydrophobic properties probably improved the structure, aggregation, and water-retention ability of the soil. Soil physical structure improvement caused by the manure application may be a result of organic matter content increase, which had a dilution effect on the soil, by bonding particles and increasing soil aggregation. Similar findings were reported by Mahmood et al. [64]. Consistent with our findings, Mbah et al. [65] reported a decrease in soil bulk density (BD) resulting from the incorporation of organic manures. Ahmad et al. [66] similarly observed that the application of organic manure, both individually and in combination with inorganic fertilizers, notably improved soil bulk density (BD), increased soil porosity, and had a beneficial effect on soil conditions by mixing organic matter into the soil, which helped to reduce the overall soil mass.
The increment in SOC as a result of FYM integration is because FYM is a rich source of organic carbon. Prior research has indicated that the application of manure is one of the most effective methods for increasing organic matter in soils and enhancing carbon sequestration [67]. Similarly, Bhogal et al. [68] observed that organic manures lead to increased carbon accumulation across various soil types and climatic conditions. The rise in soil organic carbon (SOC) content in plots treated with organic manures can be attributed to the accumulation of organic matter, which subsequently modifies the physical, chemical, and biological properties of the soil [69]. The role of organic manure in the accumulation of soil organic carbon (SOC) and carbon sequestration has been documented by Are et al. [70]. The enhancement in STN can be linked to the mineralization and residual effects of organic manure, which increased the nitrogen levels in the soil. Our findings are supported by Bhat [71], who noted that nitrogen from organic sources contributed to an increase in STN. Additionally, Iqbal et al. [5] demonstrated that organic manures positively influence soil quality compared to inorganic fertilizers, leading to increased nutrient release and availability (particularly nitrogen) for crop plants. Similarly, Farid et al. [72] reported that the incorporation of organic nitrogen sources significantly enhanced chemical properties, such as soil organic matter and total nitrogen, there was minimal impact from artificial or mineral sources. The application of nitrogen from organic sources also significantly boosted SMN. The increased availability of nitrogen in plots amended with organic materials may be attributed to the enhanced nitrogen mineralization from these organic sources. Tabassum et al. [73] also reported elevated SMN levels due to the incorporation of organic amendments. Additionally, Alizadeh [74] observed that soil amended with PM exhibited significantly higher nitrogen mineralization compared to other organic sources. Furthermore, Cordovil et al. [75] pointed out that variations in nitrogen mineralization across different sources of organic manure may be due to differences in animal diets and the carbon-to-nitrogen (C/N) ratios of the organic materials. Poultry, which mainly feeds on grains and protein-rich cakes, generally exhibits a lower carbon-to-nitrogen (C/N) ratio compared to cattle, which predominantly consume forages and straws that possess a higher C/N ratio [76]. Consequently, organic materials with a low carbon-to-nitrogen (C/N) ratio encourage nitrogen mineralization [77], whereas those with a higher C/N ratio tend to promote nitrogen immobilization [78]. The observed decrease in soil pH in soils amended with organic manures can primarily be attributed to the release of organic acids during the decomposition of these materials. Furthermore, the nitrification process, which produces hydrogen ions that are subsequently released into the soil solution, may be connected to the observed decrease in soil pH with increasing nitrogen rates [79]. Furthermore, soil electrical conductivity (EC) was significantly influenced by nitrogen management, with the highest EC recorded in the control group, followed by plots treated with poultry manure (PM), farmyard manure (FYM), and urea. Comparable results were also noted by Kawsar et al. [61].
The interactive effect of BC and N management in improving soil chemical properties can be described by the fact that incorporation of manures with BC might help in surface oxidation of BC by higher temperature, especially at the start of the process. Further, it also modifies BC characteristics biotically due to the greater microbial activity during the decomposition of available carbon sources. Similar results were also obtained by [80].

5. Conclusions

The integration of biochar and nitrogen management represents a transformative approach to enhancing soil health and fertility. This study reveals that the combined application of biochar and nitrogen not only improves soil physical and chemical properties but also optimizes their interactive benefits. The significant reduction in soil bulk density and increase in moisture content achieved through biochar application highlights its potential as a soil amendment that enhances soil structure and water retention. Concurrently, nitrogen management, particularly from organic sources, amplifies these benefits by further enriching soil organic carbon, nitrogen, and improving soil pH. The synergistic effects observed from combining biochar with nitrogen management suggest a robust strategy for sustainable soil fertility management. The potential for biochar to modulate soil pH and electrical conductivity, coupled with nitrogen’s role in increasing soil nutrient content, offers a dual approach to addressing soil degradation and enhancing agricultural productivity. These findings not only contribute to the understanding of soil amendment interactions but also offer practical implications for agricultural practices. The ability to significantly improve soil conditions through tailored biochar and nitrogen applications presents a promising avenue for advancing soil management strategies and achieving sustainable agricultural systems. This integrated approach could serve as a model for future research and practical applications in soil fertility and environmental stewardship.

Author Contributions

Conceptualization, M.A.K. and A.B. (Abdul Basir).; methodology, S.T.S., and M.H..; software, M.U.R..; validation, Y.H.D., R.M., A.J. and E.R..; formal analysis, H.Z..; investigation, M.A.K., A.B. (Abdul Basir), and M.U.H..; resources, A.J..; data curation, H.Z.., A.J., Y.H.D., and S.T.S.; writing—original draft preparation, A.B (Abdul Basit)., M.A.AK., M.U.H., H.Z., M.U.R., and A.B. (Abdul Basir). ; writing—review and editing, A.J., Y.H.D.., E.R.., R.M., and S.T.S.; visualization, Y.H.D.; supervision, S.T.S..; project administration, A.J..; funding acquisition, R.M and A.J.. All authors have read and agreed to the published version of the manuscript.

Funding

Researchers Supporting Project number (RSP-2024R375), King Saud University, Riyadh, Saudi Arabia.

Data Availability Statement

The datasets used and/or analyzed during the current study are available from the corresponding authors on reasonable request.

Acknowledgments

The authors acknowledge the Researchers Supporting Project number (RSP-2024R375), King Saud University, Riyadh, Saudi Arabia.

Conflicts of Interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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Figure 1. BC × N interaction over years for soil organic carbon after harvest of wheat crops. The error bars represent standard error.
Figure 1. BC × N interaction over years for soil organic carbon after harvest of wheat crops. The error bars represent standard error.
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Figure 2. BC × N interaction over years for soil organic matter after harvest of wheat crops. The error bars represent standard error.
Figure 2. BC × N interaction over years for soil organic matter after harvest of wheat crops. The error bars represent standard error.
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Figure 3. BC × N interaction over years for soil moisture content after harvest of wheat crop. The error bars represent standard error.
Figure 3. BC × N interaction over years for soil moisture content after harvest of wheat crop. The error bars represent standard error.
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Figure 4. BC × N interaction over years for soil total nitrogen after harvest of wheat crops. The error bars represent standard error.
Figure 4. BC × N interaction over years for soil total nitrogen after harvest of wheat crops. The error bars represent standard error.
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Figure 5. BC × N interaction over years for soil mineral nitrogen content after harvest of wheat crop. The error bars represent standard error.
Figure 5. BC × N interaction over years for soil mineral nitrogen content after harvest of wheat crop. The error bars represent standard error.
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Figure 6. BC × N interaction over years for soil pH after harvest of wheat crops. The error bars represent standard error.
Figure 6. BC × N interaction over years for soil pH after harvest of wheat crops. The error bars represent standard error.
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Figure 7. BC × N interaction over years for soil EC after harvest of wheat crops. The error bars represent standard error.
Figure 7. BC × N interaction over years for soil EC after harvest of wheat crops. The error bars represent standard error.
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Table 1. Soil organic carbon (g kg-1), organic matter (%), bulk density (g cm-3) and soil moisture content (%) as affected by BC and N management.
Table 1. Soil organic carbon (g kg-1), organic matter (%), bulk density (g cm-3) and soil moisture content (%) as affected by BC and N management.
Biochar (t ha-1) SOC SOM SBD SMC
0 0.502 d 0.864 d 1.599 a 7.174 d
10 0.641 c 1.102 c 1.563 b 9.152 c
20 0.742 b 1.277 b 1.352 c 10.603 b
30 1.111 a 1.911 a 1.143 d 15.876 a
LSD (P≤0.05) 0.011 1.21 0.018 0.12
Nitrogen Management (kg ha-1)
Control 0.520 g 0.894 g 1.565 a 7.423 h
90 N Urea 0.626 f 1.077 f 1.535 b 8.948 g
120 N Urea 0.673 e 1.157 e 1.533 b 9.608 f
150 N Urea 0.708 d 1.218 d 1.503 c 10.115 e
90 N FYM 0.853 b 1.468 b 1.402 3 12.185 bc
120 N FYM 0.858 b 1.475 b 1.320 g 12.257 b
150 N FYM 0.926 a 1.593 a 1.244 h 13.235 a
90 N PM 0.724 d 1.245 d 1.430 d 10.343 e
120 N PM 0.763 c 1.312 c 1.359 f 10.901 d
150 N PM 0.840 b 1.445 b 1.250 h 12.001 c
LSD (P≤0.05) 0.018 0.03 0.028 2.26
2015-16 0.721 b 1.240 b 1.445 10.302 b
2016-17 0.777 a 1.337 a 1.383 11.101 a
Interaction P≤0.05 P≤0.05 P≤0.05 P≤0.05
BC x N Figure 1 Figure 2 Ns Figure 3
SOC: soil organic carbon; SOM: soil organic matter, SBD: soil bulk density; SMC: soil moisture content, N: nitrogen, FYM: farmyard manure, PM: poultry manure; BC: biochar. Different lowercase letters denote significant variations among treatments (P ≤ 0.05).
Table 2. Effect of biochar (BC) and nitrogen (N) management on total soil nitrogen (g kg⁻¹), mineral nitrogen (mg kg⁻¹), pH levels, and electrical conductivity (dS m⁻¹).
Table 2. Effect of biochar (BC) and nitrogen (N) management on total soil nitrogen (g kg⁻¹), mineral nitrogen (mg kg⁻¹), pH levels, and electrical conductivity (dS m⁻¹).
Biochar (t ha-1) STN SMN pH EC
0 0.073 b 28.88 c 7.52 a 0.740 a
10 0.075 b 29.65 c 7.50 b 0.738 b
20 0.078 a 30.59 b 7.46 c 0.733 c
30 0.080 a 31.50 a 7.51 ab 0.724 d
LSD (P≤0.05) 0.003 1.10 0.04 0.0004
Nitrogen Management (kg ha-1)
Control 0.063 e 24.72 g 7.59 a 0.782 a
90 N Urea 0.073 d 28.84 f 7.59 a 0.720 f
120 N Urea 0.073 d 28.86 f 7.53 b 0.713 g
150 N Urea 0.081 ab 31.98 bc 7.44 d 0.693 h
90 N FYM 0.074 d 29.16 ef 7.58 a 0.739 d
120 N FYM 0.076 cd 30.25 de 7.50 b 0.730 e
150 N FYM 0.083 a 32.66 ab 7.40 e 0.721 f
90 N PM 0.078 c 30.63 cd 7.57 a 0.760 b
120 N PM 0.079 bc 31.06 cd 7.47 c 0.748 c
150 N PM 0.085 a 33.39 a 7.35 f 0.733 e
LSD (P≤0.05) 0.003 1.36 0.02 0.003
2015-16 0.074 b 29.2 b 7.49 0.734 b
2016-17 0.079 a 31.1 a 7.52 0.735 a
Interaction P≤0.05 P≤0.05 P≤0.05 P≤0.05
BC x N Figure 4 Figure 5 Figure 6 Figure 7
STN: soil total nitrogen; SMN: soil mineral nitrogen, EC: electrical conductivity; N: nitrogen, FYM: farmyard manure, PM: poultry manure; BC: Biochar. Different lowercase letters indicate significant variations among treatments (P ≤ 0.05).
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