Evaluating biochar’s potential to reduce nitrate leaching and enhance wheat (Triticum aestivum L.) yield under different nitrogen management practices

Abstract

Nitrate (NO₃^-) leaching from alkaline coarse-textured agricultural soils is a major concern that reduces nitrogen use efficiency (NUE) and limits crop productivity. Application of biochar has been found to improve soil fertility through nutrient retention when used with nitrogen fertilizer, however, its efficacy in coarse-textured alkaline soil is insufficiently explored. A greenhouse pot experiment was carried out comprising completely randomized design (CRD) with five treatments and three replicates (15 pots) to investigate the effects of biochar applied with N doses on NO₃^- leaching, N uptake and wheat yield. The treatments consisted of T1 (Control), T2 (Nitrogen 75 kg ha^-1), T3 (Nitrogen 150 kg ha^-1), T4 (2% biochar + Nitrogen 75 kg ha^-1), and T5 (2% biochar + Nitrogen 150 kg ha^-1). Biochar application had significantly reduced NO₃^- leaching compared to no biochar with T4 and T5 showing the lowest levels of NO₃^- losses. All the biochar applied treatments produced high grain yield, N uptake, and improved NUE in terms of treatments with no biochar applied. The decrease in NO₃^- leaching was coupled with increased N retention in the soil and enhanced plant growth parameters. This research indicates that 2% biochar with 150 kg N ha^-1 is the most effective treatment to ensure maximum wheat production and reduces NO₃^-- leaching in alkaline coarse-textured soils.

Supplementary Information

The online version contains supplementary material available at 10.1038/s41598-026-53870-0.

Introduction

Nitrogen losses in the soil–plant system not only diminish soil fertility and crop yield but they can also negatively impact the environment¹. However, when the supply of N surpasses crop demand, environmental contamination results². The mineral N in the soil is easily removed by crops, immobilized, and lost to the environment by volatilization, surface runoff, and leaching³. Compared to NH₄ in alkaline, dry, and semiarid environments, soil native charged colloids are predominantly negatively charged. These colloids hinder nitrate (NO₃^-) from absorbing ⁺on their surfaces. This phenomenon accelerates the downward movement of NO₃^- along with drainage water, leading to its rapid leaching into the soil⁴.

The application of N fertilizer has exceeded its optimal levels. Due to its solubility, nitrate has a mobilized nature and potential for soil loss due to leaching⁵. Croplands subjected to substantial agricultural practices emerge as the predominant origin of leached nitrogen (NO₃^-) in the environment⁶. NO₃^--N leaching is found to be profoundly impacted by the composition of the soil and prevailing climatic conditions. A notable instance of this phenomenon was observed in sandy soil, where an application of 87 kg N ha^-1 led to substantial NO₃^- leaching, as opposed to the 10 kg N ha^-1 observed in loamy soils⁷.

Wheat (Triticum aestivum L.), a globally important cereal crop and staple food source, has a high N demand making it particularly vulnerable to N losses through leaching in sandy soils^8,9. Thus, optimization of N use and loss reduction in wheat-based systems is essential to attain sustainable agricultural production, especially in areas where alkaline sandy loam soils predominate.

The process of NO₃^- leaching can be mitigated through various management practices, including optimized N application timing, cover cropping, and the use of soil amendments. Among these, the application of biochar has recently garnered increased interest due to its dual benefits of mitigating climate change and enhancing soil quality¹⁰. Biochar is a carbon-rich solid produced by pyrolysis of biomass under limited oxygen conditions¹¹. This organic source has been demonstrated to reduce nitrogen leaching through the enhancement of the soil’s cation exchange capacity (CEC) and anion exchange capacity (AEC)¹².

Despite extensive research on biochar for soil fertility and nutrient retention, its effect on NO₃^- leaching in coarse-textured alkaline soils remains insufficiently investigated. Furthermore, the interaction between biochar and N application under controlled conditions that isolate N dynamics has received little attention, leaving key mechanisms poorly understood. Consequently, the processes through which biochar affects the retention of N and the provision of N to plants in such soils are not well established.

The role of biochar in improving N retention in alkaline sandy loam soils is a promising strategy in enhancing the efficiency of N use and reducing environmental losses in cereal-based production systems. Therefore, Controlled greenhouse pot experiment was thus required as a pilot study to show the potential of biochar as a nitrogen retaining amendment before the more complex field-scale studies were undertaken.

Our hypothesis was that the application of biochar in alkaline sandy loam soil would decrease NO₃^- leaching and enhance the retention of soil N, thus optimizing the growth and yield of wheat under N-fertilized conditions. With this hypothesis our objectives were: (1) to quantify biochar effect on NO₃^- leaching and (2) to determine its impact on post-harvest soil and plant N concentrations, total N uptake and wheat yield in a controlled greenhouse experiment . The novelty of this research lies in its focus on alkaline sandy loam soil — a coarse textural class characterized by inherently low nutrient retention and less N availability to plants. Addressing this knowledge gap is essential for developing sustainable N management strategies in these soils, where fertilizer losses are high and crop productivity is often limited.

Materials and methods

Description of the experiment

Random soil samples were collected using auger from a depth of 0–20 cm at the Agricultural Research Farm of the University of Agriculture, Peshawar. After air-drying, the debris was subjected to a sieving process utilizing a 2-mm filter. A sand:soil mixture (2:1, w/w) was made to simulate a coarse-textured soil with high potential for NO₃^- leaching. This practice was specifically aimed at increasing microporosity and hydraulic conductivity in controlled environments to produce a leaching-prone environment to be used in assessing N dynamics. The experiment was performed in plastic pots with a 12 inches diameter (30 cm height × 30.5 cm diameter) filled with 10 kg of the prepared sand soil mixture (2:1). The bulk density of the soil was set to 1.42 g cm^-3. Soil sample from the top 10 cm in the pots were thoroughly mixed with N and biochar levels. The pots were marked at two distinct heights, corresponding to soil depths of 10 cm and 20 cm, respectively. All pots were thoroughly hydrated with 1 L of water. Ten wheat seeds were planted in each pot, and the five most vigorous plants were selected for further study. Leachate samples were collected at 14, 24, 34 and 74 days after sowing (DAS). The first three leachate samples were collected at 10-day intervals to monitor early N leaching, while the final sample was collected at 74 DAS to evaluate late-season leaching as the crop matured. Each pot was saturated with 200 ml of distilled water 24 h prior to leachate collection. Leachate collected from all the pots was further analyzed to ascertain its pH, electrical conductivity (EC), mineral nitrogen (MN), and nitrate nitrogen (NO₃^--N) concentrations. Subsequent to the harvesting, soil samples were collected from the pots at depths of 10 cm and 20 cm for analyzing various parameters, including pH, electrical conductivity (EC), and NO₃^--N.

Physico-chemical properties of the soil

The soil is characterized by a textural class of sandy loam, comprising 56.5% sand, 34.1% silt, and 9.4% clay. The pH of 8.1 indicates that the soil is significantly alkaline, exhibiting an EC of 0.17 dSm^-1. This soil had relatively lower levels of organic matter (0.36%) and moderate N content (0.049%).

Irrigation levels and water management

Water holding capacity was determined as 23.6 ± 1.8%(v/v) indicating the coarse texture of the growth medium. Irrigation was done in a measured volumetric method with distilled water to ensure uniformity in the soil moisture content across treatments. Water was added manually using a graduated cylinder. Each pot was given 1 L of water at sowing. During the growth phase, 250 mL of water was added after every three days, maintaining approximately 50–60% of WHC to mimic moderate conditions of moisture and avoid water stress. Furthermore, 200 mL of water was given to all the pots 24 h prior to leachate collections (14, 24, 34 and 74 DAS) to ensure the consistency in percolation and measurable amounts of leachates. The amount of leachate collected was measured at every collection point, and subsamples were tested to determine the concentration of NO₃^--N.

Biochar used for the experiment

The biochar used in this experiment was derived from mixed hardwood feedstock (primarily sheesham and poplar) in the form of wood ash. It was produced using “on farm” method by slow pyrolysis at 550 °C over 2 h under limited oxygen conditions, as has been done under the conventional biochar production protocols using woody biomass¹³. The process consists of two cylindrical cores (drums), one external to produce heat and other internal where feedstock is placed to produce biochar through pyrolysis. The biochar was prepared and used after being sieved to a particle size of less than 2 mm,¹⁴. Table 1 summarizes some of the important physicochemical characteristics of the hardwood biochar.

Table 1.

Physiochemical characteristics of the hardwood biochar.

Properties	Unit	Concentration
Feedstock	–	Mixed hardwood
Pyrolysis temperature	°C	550
pH (1:20 biochar:water)	–	10.2
Electrical Conductivity (EC)	dS m-1	3.5
Ash content	%	25.8
Total carbon (C)	%	58.6
Total nitrogen (N)	%	0.9
Cation Exchange Capacity (CEC)	cmol+ kg-1	32.1
Anion Exchange Capacity (AEC)	cmol− kg-1	5.3
Porosity	%	48

A biochar application (2% w/w) was chosen in regard to past research that has indicated that low to moderate levels of biochar (1–3%) are effective in enhancing nutrient retention and reducing nitrate leaching in sandy-to-sandy loam soils, without having excessive effects on soil pH or salinity¹⁵. Since the experimental soil was alkaline (pH 8.1), it was purposely avoided to raise the biochar rates to prevent the possible negative impact on the availability of the nutrients.

NO₃^--N losses

In order to measure the total amount of nitrogen loss through leaching during the wheat growing period, cumulative nitrate-nitrogen (NO₃^--N) loss was estimated in each pot using following formula.

C = concentration of NO_₃^--N (mg L^-1), V = Volume of Leachate (L) i = leachate collection events i.e. 1,2 3, and 4. The volume of collected leachate was measured at four leaching events (14 DAS, 24 DAS, 34 DAS, and 74 DAS), and a subsample was analyzed for NO₃^--N concentration (mg L⁻¹).

Physio chemical attributes of the soil

The soil pH and EC were determined in a 1:5 soil suspension. 10 g of soil were stirred in a conical flask with 50 ml of water for 25 min. Then, the pH and EC were determined using a pH meter and an EC meter, respectively, according to the methods proposed by Kuo¹⁶, McLean¹⁷ and Richards.¹⁸. To determine the soil texture, a 50 g sample of soil was blended with 10 ml of Na₂CO₃ in a dispersion machine for five minutes. Hydrometer measurements were taken after 40 s and two hours¹⁸. The procedure established by Gee¹⁹, Nelson and Sommers²⁰ was used to calculate the amount of organic matter in the soil. Ten milliliters of 0.5 N potassium dichromate and 20 ml of concentrated sulfuric acid (H₂SO₄) were combined with 1 g of soil. The mixture was allowed to cool for around 30 min. After cooling, 200 mL of distilled water was added, and the liquid was filtered. The filtrate was titrated against 0.5 N ferrous sulfate (FeSO₄) in the presence of two to three drops of ortho phenolphthalein indicator until a color shift occurred. The given formula was used to compute the organic matter content.

Mineral nitrogen in soil

Mineral nitrogen (MN) was determined using a KCl solution and identified using Nelson²⁰, Keeney et al.²¹ steam distillation technique. MN was found to be in the forms of NH₄⁺-N and NO₃^--N. Using this approach, 20 g of soil from each pot after harvest were agitated for one hour with 100 ml of 1 M KCl solution. Then, the soil was filtered through Whatman-42. To analyze NH₄⁺-N or NO₃^--N, 20 mL of the filtrate was distilled using MgO or MgO + Devardas alloy. In all cases, the N was collected in a 5-ml solution of mixed indicators and boric acid until the level reached 75 ml. Then, it was titrated against 0.005 N HCl until a pink color appeared. 70 μg N mL^-1 corresponded to one milliliter of 0.005 N HCl. The NO₃^--N concentration was determined by subtracting the NH₄⁺ concentration from the NO₃^- + NH₄⁺ concentration.

Post harvest analysis

Total nitrogen in plant

To appraise the nitrogen content of the plant, the Kjeldhal approach was utilized, as suggested by Keeney²¹, Bremner et al.²². 0.2 g of pulverized leaf and stem mixed plant material was placed within the digestion tubes. Then, 1.1 g of the digestion mixture was added. This mixture was a 100:10:1 combination of K₂Cr₂O₇, CuSO₄, and Se. After adding 3 cc of H₂SO₄, the tubes were placed in a block digester and allowed to digest for three hours at 450 °C.Twenty milliliters of the absorb solution were distilled using a five-milliliter boric acid mixed indicator containing two indicators: methyl red and bromochresol green. Then, the distillate was titrated against 0.005 M HCl to measure NH₄⁺. The following formulas was used

Agronomic parameters

At harvest, the plant height was measured using a measuring tape by selecting randomly three highest plants from each pot, and their average heights were recorded. Spike length(cm) was determined at peak maturity by measuring randomly selected three spikes. The number of grains per spike was calculated by averaging the grain count of five spikes per pot. The 100-grain weight was measured using an electronic balance by weighing 100 grains from every pot. Grain yield, was determined by weighing the threshed and dried grains in each pot. The biological yield was assessed by measuring the total dry weight of the aboveground plant biomass in each pot at harvest.

Statistical analysis

The obtained data were then statistically analyzed using ANOVA (Analysis of Variance) by using Statistix 8.1 software for the completely randomized design (CRD). The least significant difference (LSD) test was employed to compare means across all treatments (p < 0.05). The letters in figures show statistically significant differences between treatment means and Tables was predicated on their relative importance²². All figure were made using Microsoft Excel 2021.

Results

Effects of nitrogen rate and biochar amendment on nitrate nitrogen (NO₃^-N)

The effect of nitrogen rate and biochar amendment on the dynamics of NO₃^--N leaching at all four sampling events (14, 24, 34, and 74 DAS) were found significant (p < 0.05) (Fig. 1a–d). The high N rate (150 kg N ha^-1) in the absence of biochar resulted in the maximum levels of NO₃^--N per leaching event that were significantly higher than the moderate N applied rate (75 kg N ha^-1) and control. Application of biochar with 75 kg N ha^-1 after 34 days of sowing resulted in a 29.0% reduction in NO₃^--N compared no biochar application. Similarly, the biochar applied in conjunction with 150 kg N ha^-1 led to a 24.2% decrease in NO₃^--N (Fig. 1c). This impact of mitigation measures was also apparent up to the final leaching event (after 74 days), during which 2%+75 kg N ha^-1 and 2%+ 150 kg N ha^-1 exhibited the lowest NO₃^--N among all fertilized treatments (Fig. 1 c and d).

Fig. 1.

Nitrate‑nitrogen (NO₃^--N) concentration (mg L⁻¹) in leachate as affected by biochar and nitrogen fertilizer rates at four leaching events: (1a) 14 days after sowing (DAS), (1b) 24 DAS, (1c) 34 DAS, and (1d) 74 DAS. The error bars are standard error (SE) of mean (n = 3). The letters above the error bars show significant difference with least significant difference at P < 0.05.

Soil mineral nitrogen and nitrogen use efficiency (NUE)

Application of N and biochar amendment had significant effects on the mineral nitrogen (mg kg^-1) and NUE in soil (p < 0.05). The 2% biochar application in combination with 150 kg N ha ^-1 recorded the highest MN concentration that was significantly higher than other treatments. The biochar applied with 75 kg N ha⁻¹ produced soil MN levels (26.69 mg kg⁻¹) that did not differ significantly from the higher N rate applied alone (28.13 mg kg⁻¹) (P > 0.05). This indicates biochar efficiency to increase N retention in soil despite lower fertilizer application rates. Similarly, the highest NUE (30.70%) was observed in the 2% biochar-amended with 75 kg N ha⁻¹, followed 150 kg N ha⁻¹ (23.77%) (Supplementary Table S1). Conversely, the non-biochar treatments exhibited lower values of NUE (Table 2).

Table 2.

Nitrogen use efficiency (%) as affected by biochar and nitrogen fertilizer rates.

Nitrogen Applications	N use efficiency (%)
Control	–
Nitrogen 75 kg ha-1	18.57 ± 10.02
Nitrogen 150 kg ha-1	13.49 ± 3.91
2%Biochar + Nitrogen 75 kg ha-1	30.70 ± 3.15
2%Biochar + Nitrogen 150 kg ha-1	23.77 ± 2.55

Values denote the mean of 3 replications. Error bar indicate the standard error (SE) of the mean (n 3).

Plant N and agronomic parameters

The application of N fertilizer and biochar had a significant impact on all growth parameters, yield, and N uptake measured in wheat (P < 0.05). The highest values for grain yield (22.76 g pot ^-1), biological yield (68.34 g pot^-1), N uptake (832.63 mg pot^-1), plant height (65.76 cm), spike length (9.06 cm), and 100-grain weight (3.39 g) were consistently achieved in 2% biochar with 150 kg N ha⁻¹ followed 75 kg N ha^-1 and was significant then no biochar treatments (Table 3).

Table 3.

Wheat nitrogen concentration (%), total N uptake (mg pot⁻¹), and agronomic parameters as affected by biochar and nitrogen fertilizer rates.

Nitrogen applications	N Concentration (%)	N uptake (mg pot-1)	Plant height (cm)	Spike length (cm)	100 grain weight (g)	Biological yield (g pot-1)	Grain Yield (g pot-1)
Control	1.03 0.03 b*	572.33 13.45 c*	51.16 0.46 c*	7.46 0.09 c*	3.02 0.01 d*	57.06 0.84 c	18.34 0.14 c*
Nitrogen 75 kg ha-1	1.09 0.07 ab	674.0 52.68 bc	53.30 0.76 c	8.10 0.21b	3.06 0.01 d	61.73 0.79 b	19.52 0.09 b
Nitrogen 150 kg ha-1	1.12 0.06 ab	720.03 42.21 b	57.96 0.84 b	8.66 0.12 a	3.16 0.01 c	64.06 0.96 b	20.34 0.12 ab
2%Biochar + Nitrogen 75 kg ha-1	1.13 0.03 ab	740.40 17.18 ab	58.30 1.56 b	8.83 0.09 a	3.27 0.04 b	65.16 0.88 ab	21.84 0.19 ab
2%Biochar + Nitrogen 150 kg ha-1	1.22 0.05 a	832.63 27.91 a	65.76 0.81 a	9.06 0.09 a	3.39 0.03 a	68.34 1.39 a	22.76 0.19 a
LSD (P < 0.05)	0.1665	110.13	2.7537	0.4599	0.0726	3.6438	1.0882

Values denote the mean of 3 replications meanwhile small letters indicates the significance differences among the treatments at P < 0.05. Error bar indicate the standard error (SE) of the mean (n 3).

NO₃^--N losses (mg pot⁻¹)

Nitrogen losses (mg pot^-1) are depicted in the Table 4. Biochar application with different levels of N significantly influences NO₃^--N losses. N applied without biochar exhibited the maximum losses during the experiment with a measured value of 9.69 mg pot^-1 by application of 75 kg N ha^-1 and 10.70 mg pot^-1 from 150 kg N ha^-1.Futhermore, 2% Biochar application with 75 kg ha ^-1 lowered the cumulative loss of NO₃^--N by 27.6% relative the same rate N applied alone. Similarly, biochar applied at the rate of 150 kg ha^-1 showed a reduction of 20.3% relative to the same rate applied without biochar (Fig. 2).

Table 4.

Cumulative NO₃^--N loss (mg pot⁻¹) and % reduction with biochar amendment.

Treatments	Cumulative NO₃--N Leaching (mg pot−1)	% Reduction in NO₃--N observed by the addition of biochar
Control	2.40 ± 0.11 c	–
Nitrogen 75 kg ha−1	9.69 ± 0.99 b	–
Nitrogen 150 kg ha−1	10.70 ± 1.05 a	–
2% Biochar + Nitrogen 75 kg -1	7.02 ± 0.17 b	27.6% reduction (compared to treatment 2)
2% Biochar + Nitrogen 150 kg -1	8.53 ± 0.76 ab	20.3% reduction (compared to treatment 3)

Values denote the mean of 3 replications meanwhile small letters indicates the significance differences among the treatments at P < 0.05. Error bar indicate the standard error (SE) of the mean (n 3).LSD (P < 0.05) = (2.36).

Fig. 2.

Post harvest mineral nitrogen (mg kg^-1) in soil as influenced by the application of biochar with different nitrogen rates. The error bars are standard error (SE) of mean (n = 3).The letters above the error bars show significant difference with least significant difference at P < 0.05.

Discussion

Nitrogen leaching from coarse-textured alkaline soils was reduced by applying 2% biochar along with different doses of N. In a controlled greenhouse pot experiment, nitrate (NO₃^-) leaching, N use efficiency, and wheat performance were assessed. The temperature was kept constant to prevent environmental impacts²³. Thus, the changes in NO₃^- leaching, NUE, and crop yield can solely be examined by the use of biochar and N applications. Our findings show that biochar retains N in the soil and reduces NO₃^- leaching primarily due to increased AEC and physical entrapment of nitrates in the biochar pores. These results are consistent with the early findings of He et al.²⁴, Luo et al.²⁵, who reported that biochar reduces NO₃^- leaching by 15–70% through mechanisms like surface adsorption, ion exchange, and pore entrapment. Application of biochar substantially enhances the physical properties of soil and nutrient retention thereby enhances the soil fertility and crop yield through nutrient availability²⁵.

Optimum N in soil is an indicator of soil fertility that is enhanced with the co-application of organic sources and inorganic fertilizers such as biochar with N fertilizer^26,27. Mineral nitrogen (MN) in soil varied with biochar application and N rates, with 2% biochar incorporating 75 and 150 kg N ha^-1 showing highest MN of 26.69 and 28.13 mg kg^-1 as compared to the sole same application rates. The change observed in MN through biochar application might be due to the characteristics of the biochar for example its high CEC and surface functional groups likely retained NH₄⁺ in the soil while its porous nature restricts N from rapid mineralization²⁸. These results confirm that co-application of biochar with N fertilizer enhances nutrient cycling and N retention in coarse-textured alkaline soils. The enhanced N retention observed in conjunction with biochar application is of particular significance, considering the role of unretained NO₃^--N in initiating cumulative N leaching and inducing environmental risks.

Excessive N fertilizer application poses environmental hazards alongside its agronomic benefits²⁹ and therefore should be given special attention. The cumulative reduction (20–28%) observed in NO₃^- through biochar application might be due to performance and properties of the biochar in retaining N in the soil with coarse texture nature. Sainju et al.³⁰, Li et al.³¹ reported that co application of biochar with N fertilizer can reduce cumulative N losses by enhancing N retention in soil depending on biochar properties. The study’s potential implication is improving N availability and reducing environmental risks by selecting a particular biochar type that improves nutrient availability with long-term stability.

Nitrogen is the most limiting nutrient for plant production. The enhancement in NUE observed in biochar- treated pots demonstrates N retention in soil taken up by plant³¹. Coarse texture soil therefore remains poor in nutrient availability³². In our study, the highest NUE was observed when 2% biochar was applied with lower N rates i.e. 75 kg N ha^-1. This indicates that biochar is particularly effective in lower rates of N due to less N losses from applied N fertilizer³³. Maximum plant N uptake also results in higher NUE showing that applied fertilizer is used effectively³⁴. The performance of biochar applied with N fertilizer in terms of NUE was higher as biochar enhances both physical properties of the soil and root development.

Plant parameters, such as N concentration , N uptake, growth and yield were significantly affected by incorporation of biochar with N fertilizer. A notable enhancement was found in all these parameters in biochar-treated pots. These improvements were attributed to several interrelated mechanisms. (i) Biochar retains MN in soil rhizosphere that is taken up by plant at early growth stages³⁵, (ii) the higher N concentration in plant tissues and uptake indicates biochar not only retains N in soil but also enhances the physiological availability³⁶ and (iii) the properties of the biochar, for example porosity and WHC maintaining a favorable condition for root proliferation³⁷.

Over the past years, there has been an increasing interest in biochar as a soil amendment to reduce NO₃^- leaching and to improve the efficiency of N-utilization³⁸. Biochar enhances N retention by increasing CEC, AEC, and providing porous surfaces for ion adsorption^39,40. As hypothesized in the present study, the application of 2% biochar significantly reduced cumulative NO₃^--N losses by 20.3–27.6% compared to N-only treatments, with the greatest reduction observed at the lower nitrogen rate of 75 kg ha^-1. The greater reduction at 75 kg N ha^-1 suggests improved synchronization between soil N supply and crop demand aligning with competing hypotheses proposed by Dey et al.⁴⁰, Sanford et al.⁴¹. In alkaline sandy loam soils, biochar can be useful as a N-limiting agent, enhancing the retention of N in forms less prone to leaching yet plant-available in the long term. Based on this, biochar application likely improved physicochemical retention, enhancing N retention and minimizing leaching losses⁴². In line with our results, Zhao et al.⁴³, Purkaystha et al.⁴⁴ found that biochar use in coarse-textured soils led to a decrease in nutrient leaching potential due to enhanced water and nutrient retention capacity. The higher retention of N in pots amended with biochar clearly led to high post-harvest soil MN and higher plant N uptake. The chemistry of biochar, along with its interactions with the soil matrix, has been demonstrated to play a pivotal role in the transformation of applied N into plant-available forms, thereby enhancing N supply and efficiency⁴⁴. Reduced NO₃^- leaching in the mid-to-late growing phase (34–74 days after sowing) was attributed to higher N retention levels due to biochar. These results emphasize the key role of biochar in alleviating NO₃^- leaching and maximizing N cycling in alkaline coarse-textured soils, and the sustainable production of wheat.

Conclusions

The research was conducted as a short-term and single-season greenhouse pot experiment; therefore, the results should be interpreted with caution when applying them to field-scale conditions. In such controlled conditions, the application of 2% biochar + 150 kg N ha^-1 in alkaline sandy loam soils was found to be effective in reducing NO₃^-leaching and improving soil N retention, resulting in enhanced wheat growth, yield, and N uptake. The biochar-amended treatments demonstrated clear advantages over the sole application of N, particularly in terms of reducing N loss and enhancing NUE at the optimal rates. However, it must be acknowledged that the controlled pot conditions may not fully capture the complexity of field conditions, including factors such as soil heterogeneity, climatic variability, and long-term biochar-soil interactions. Consequently, further research is required in a range of field-based investigations, encompassing various soil types and agroecological settings, in order to substantiate the longevity and scalability of these effects. Overall, the results suggest that biochar has strong potential as a sustainable soil amendment for improving N management in coarse-textured alkaline soils. However, its practical application would be best guided by field validation and site-specific considerations.

Supplementary Information

Below is the link to the electronic supplementary material.

Author contributions

M.U. designed the experiment, collected data,. Z.K. wrote the initial draft of the manuscript analyzed the data. A.N. assisted with the experimental setup. A.K.J. provided guidance and contributed to data interpretation.

Funding

The authors declare that no funding was received for this research.

Data availability

The datasets generated during and/or analyzed during the current study are available from the corresponding author upon reasonable request.

Declarations

Competing interests

The authors declare that there are no competing interests.

Declaration of Generative AI and AI-Assisted Technologies in the Writing Process

uring the preparation of this work, the author(s) used ChatGPT (OpenAI) to support the writing process by refining grammar, enhancing clarity, and improving the structure of selected sections of the manuscript. After using this tool, the author(s) reviewed and edited the content as needed and take full responsibility for the content of the published article.