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ISSN : 2287-5824(Print)
ISSN : 2287-5832(Online)
Journal of The Korean Society of Grassland and Forage Science Vol.45 No.1 pp.82-88
DOI : https://doi.org/10.5333/KGFS.2025.45.1.82

Wood Biochar Enhances Nitrogen Retention and Mitigates Ammonia and Nitrous Oxide Emissions from Pig Slurry during the Vegetative Growth of Rapeseed

Sang-Hyun Park1, Muchamad Muchlas1,2, Tae-Hwan Kim1, Bok-Rye Lee1*
1Grassland Science Lab, Department of Animal Science, Institute of Agricultural Science and Technology, College of Agriculture
& Life Science, Chonnam National University, Gwangju 61186, Korea
2Faculty of Animal Science, University of Brawijaya, Veteran Street, Malang, East Java 65145, Indonesia
* Corresponding author: Bok-Rye Lee, Grassland Science Lab, Department of Animal Science, Institute of Agricultural Science and Technology, College of Agriculture & Life Science, Chonnam National University, Gwangju 61186, Korea Tel: +82-62-530-0217, Fax: +82-62-530-2129, E-mail: turfphy@jnu.ac.kr
March 3, 2025 March 24, 2025 March 25, 2025

Abstract


The utilization of pig slurry (PS) as an organic fertilizer plays a pivotal role in nutrient recycling within agricultural systems. However, this practice concomitantly leads nitrogen (N) losses through ammonia (NH₃) volatilization and nitrous oxide (N₂O) emissions. The objective of this study was to investigate the effect of wood biochar on mitigating NH3 and N2O emissions and enhancing N retention from PS-applied soil, and plant biomass production during the vegetative growth of rapeseed (Brassica napus L.). The experiment consisted of three treatments: 1) water (non-PS), 2) PS, and 3) PS combined with wood biochar (PS+WB). The PS+WB treatment resulted in the maintenance of elevated soil water content during the experimental period. The PS+WB treatment significantly enhanced soil nitrogen retention compared to PS alone, maintaining higher total N and NH₄⁺-N levels while reducing NO₃⁻ -N accumulation. Wood biochar application also leds to substantial reductions in NH₃ and N₂O emissions, mitigating environmental N losses. The PS+WB treatment resulted in an improvement of shoot biomass, crude protein content, and total digestible nutrients, indicating enhanced forage quality. The increased soil moisture content in PS+WB further contributed to plant growth benefits. These findings demonstrate that wood biochar is an effective amendment for improving nitrogen retention, reducing gaseous N emissions, and enhancing crop productivity in PS-amended soils.


Ammonia , Nitrogen retention , Nitrous oxide , Pig slurry , Rapeseed , Wood biochar

초록

    Ⅰ. INTRODUCTION

    The rapid expansion of animal production to satisfy global food demand has resulted in a substantial increase in livestock waste generation. In Korea, the livestock population has steadily increased and annual livestock waste production has reached 50.8 million tons, with pig waste constituting the largest share at 19.2 million tons (MAFRA, 2024). Pig slurry (PS), comprising 95% of pig waste, is a crucial nutrient source for agriculture. However, the decline in available arable land has introduced challenges to its sustainable management, often resulting to soil nutrient accumulation and water contamination.

    The utilization of PS in agricultural settings is a matter of concern, as it has been demonstrated to result in substantial environmental hazards. This is primarily attributable to the high levels of ammonium (NH₄⁺) and organic nitrogen present in the compound (Lee et al., 2021;Banik et al., 2023). The process of transformation of NH₄⁺ in PS into ammonia (NH₃) is a rapid one, and the resultant ammonia is prone to volatilization into the atmosphere. This phenomenon contributes to nitrogen loss, which in turn exacerbates air pollution and soil acidification. The nitrification of NH₄⁺ is of particular concern due to their role in atmospheric particulate formation and negative impacts on air quality and human health (Zhang et al., 2021). Nitrogen oxides (NO and NO₂) and nitrous oxide (N₂O), a potent greenhouse gas that exacerbates climate change (Wang et al., 2024). Moreover, nitrification converts NH₄⁺ into nitrate (NO₃⁻), which, if not efficiently taken up by plants, can leach into groundwater, leading to nitrogen loss and water quality degradation (Beeckman et al., 2018). Despite these environmental concerns, PS remains an important agricultural input due to its rich macronutrient content and beneficial microbial communities (Zhang et al., 2021). Its application in crop production has been shown to enhance soil fertility, improve soil physicochemical properties, and increase crop yields (Lee et al., 2022;Shakoor et al., 2022). Therefore, developing strategies to optimize PS utilization while minimizing its environmental pollution is essential for promoting sustainable agricultural practices.

    Biochar is a carbon-rich material that has proven to be a costeffective solution with a wide range of applications in natural ecosystems. Its characteristics, including extensive surface area, microporous structure, and a high ion exchange capacity, have led to its exploration in various field, particularly in agronomic studies for soil amendment and carbon sequestration (Huang et al., 2019). Biochar has also emerged as a promising soil amendment for reducing N losses and improving nitrogen use efficiency (NUE) due to its high porosity, large surface area, and ability to adsorb NH₄⁺ and NO₃⁻ (Ghorbani et al., 2022; Park et al., 2024a). Among the various biochar types, wood biochar has been shown to possess distinct advantages over crop residue-based biochars due to its enhanced stability, high cation exchange capacity (CEC), and improved sorption properties (Rangabhashiyam and Balasubramanian, 2019; Hu et al., 2021). The production of wood biochar typically occurs at higher pyrolysis temperatures, resulting in a highly porous carbon matrix with strong adsorption potential for N compounds. This property effectively reduces NH₃ volatilization and minimizes N₂O emissions (Ippolito et al., 2020). Furthermore, the inherent hydrophobic nature of wood biochar enhances soil water retention, which plays a critical role in stabilizing N availability and supporting plant growth under various moisture conditions. However, the potential benefits of wood biochar, particularly in PS-amended soils during crop cultivation, remain underexplored. Unlike other amendments, wood biochar can serve as a long-term carbon sink, improving soil structure and microbial habitat over extended periods . These properties suggest that wood biochar may offer superior benefits in reducing N losses and enhancing soil fertility when compared to conventional amendments such as zeolite or low-temperature biochars .

    In this study, we hypothesized that wood biochar application (i) significantly reduces NH₃ and N₂O emissions by adsorbing NH₄⁺, (ii) enhances soil N retention by increasing NH₄⁺ and NO₃⁻ availability, and (iii) improves plant biomass production due to its water-holding capacity and long-term soil improvement effects. To test these hypotheses, we conducted a comprehensive analysis of NH₃ and N₂O emissions, soil NH₄⁺ and NO₃⁻ amount, and plant biomass production were analyzed during the vegetative growth of rapeseed (Brassica napus L.) in PS-amended soil.

    Ⅱ. MATERIALS AND METHODS

    1. Soil and material preparation

    The soil utilized in this study was obtained from an agricultural site in proximity to the Faculty of Agriculture, Chonnam National University, South Korea. The soil underwent a drying process in which it was exposed to the ambient atmosphere. Pig slurry used in the study was obtained from a local farm, and its nutrient composition was analyzed prior to application. The wood biochar (WB) utilized in this study was supplied by Sanglim (Ari Biochar, Korea).

    2. Experimental design

    The seeds of Brassica napus L. (cv. Mosa) were germinated in soil trays and cultivated under greenhouse conditions with a 16-hour light/8-hour dark cycle, an average daytime temperature of 27°C, nighttime temperature of 20°C, and a relative humidity of 60–70%. At the four-leaf stage, seedlings were transplanted into square pots (502 mm × 315 mm × 230 mm) filled with 21 kg of sieved soil. The experimental treatments consisted of non-PS (water), PS alone and PS combined with 10% (w/w) wood biochar (PS+WB). Pig slurry was applied at a rate of 300 kg N ha⁻¹, with additional chemical fertilizers supplied to maintain a P₂O₅:K₂O ratio of 150:150 kg ha⁻¹. Each treatment was conducted in triplicate, with daily irrigation to maintain approximately 80% of field capacity. Soil moisture levels were monitored using a portable soil moisture meter (WT-1000H, Mirae E&I, Seoul, Korea) every morning at 08:00 a.m. before evaporation occurred.

    3. Sample collection: forage, soil, and gas

    Forage samples were harvested 43 days after treatment, with shoots cut into 20-mm segments, lyophilized, ground, and stored in a vacuum desiccator for further analysis. Soil samples were collected at 0–15 cm depth using a 2.5 cm diameter auger on days 17, 22, 32, 39, and 43. Subsequently, the samples were subjected to air-dring and stored within a controlled environment until analysis. The measurement of gaseous emissions, specifically ammonia (NH₃) and nitrous oxide (N₂O), was conducted through the utilization of airtight chambers positioned at a depth of 5 cm below the soil surface (Park et al., 2024b). NH₃ emissions were trapped in 0.2 M H₂SO₄ using a vacuum system operating at 1.5 L min⁻¹, while N₂O was sampled with syringes and stored in 10 mL Vacutainer tubes for gas chromatography analysis. Gas sampling was conducted daily at 09:00 a.m. to minimize diurnal fluctuations.

    4. Chemical and analytical methods

    Soil total nitrogen (N) content was determined using the Kjeldahl method (Bremner, 1996), while NH₄⁺-N and NO₃⁻-N were extracted using 2 M KCl and analyzed via distillation with MgO and Devarda’s alloy, respectively (Lu, 2000). The crude protein (CP) was determined according to the Association of Official Analytical Chemists (AOAC, 1990). Acid detergent fiber (ADF) was measured in accordance with the methodology established by Van Soest et al. (1991). Total digestible nutrients (TDN) were estimated using the following equation:

    TDN       =       88.9       -       (0.779       ×     % ADF)

    5. Measurement of NH₃ and N2O emissions

    Ammonia (NH₃) collected in the acid trap solution was converted to ammonium sulfate ((NH₄)₂SO₄) and quantified using Nessler’s ammonium color reagent (Sigma-Aldrich, USA) following the procedure outline by Kim and Kim (1996). The N₂O concentrations were measured via gas chromatography (GC; No. 7890A, Agilent Technologies, USA) equipped with an electron capture detector (ECD) and an HP-Plot 5A column (30 m × 0.53 mm × 25 μm). Helium (He) was used as the carrier gas, with a flow rate of 2 mL min⁻¹. N₂O fluxes were calculated using the method described by Guo et al. (2012). The cumulative NH₃ and N₂O emissions over the course of the experiment were determinedd by summing daily measurements.

    6. Statistical analysis

    The experiment followed a completely randomized design with three replications per treatment. The collected data underwent rigorous analysis using Duncan’s multiple range test in SAS 9.1.3 (SAS Institute, Cary, NC, USA). This test was performed at a significance level of p<0.05.

    Ⅲ. RESULTS

    1. Soil water content

    Soil water content exhibited variation among treatments over the experimental period (Fig. 1). The pig slurry (PS) combined with wood biochar (PS+WB) treatment consistently maintained higher soil water content compared to the PS alone and water control treatments. This suggests that wood biochar showed a significant improvement in soil moisture retention, probably due to its high porosity and ability to reduce evaporation losses.

    2. Soil nitrogen dynamics

    Table 1 presents the changes in total nitrogen (Total N), ammonium nitrogen (NH₄⁺-N), and nitrate nitrogen (NO₃⁻-N) over the 43-day experimental period. The PS+WB treatment exhibited significantly higher total N content in the soil compared to the PS-only and water treatments. On day 17, the total N content in PS+WB reached 2.65 g N kg⁻¹, which was 65.6% higher than in PS-only (1.60 g N kg⁻¹). The NH₄⁺-N content showed a sharp increase in both PS and PS+WB treatments after application. However, NH₄⁺-N levels in the PS+WB treatment remained consistently higher than in PS alone, particularly from day 22 onward. On day 43, the levels of NH₄⁺-N were higher in in the PS+WB (34.4 mg N kg⁻¹) than those in the PS-only treatment(26.2 mg N kg⁻¹), indicating wood biochar delayed ammonium depletion, enhancing nitrogen retention. Conversely, accumulation of NO₃⁻-N was lower in PS+WB than in PS-only treatment. On day 43, NO₃⁻-N concentration in PS+WB was 21.6 mg N kg⁻¹, whereas in PS it was 26.7 mg N kg⁻¹.

    3. Ammonia (NH3) and nitrous oxide (N2O) emissions

    Ammonia (NH₃) emissions peaked within the initial 10 days after treatment across all treatments, with the highest emissions observed in the PS-only treatment (Fig. 2). However, PS+WB significantly reduced both daily and cumulative NH₃ emissions throughout the experiment. Nitrous oxide (N₂O) emissions followed comparable trend, with PS+WB exhibiting significantly lower emissions compared to PS-only (Fig. 3). The N2O emission in PS-only treatment showed a rapid decrease until day 19, whereas in the PS+WB treatment, this decline occurred only during the first 5 days. Cumulative N₂O emissions were significantly reduced in the PS+WB treatment, underscoring biochar’s role in stabilizing soil nitrogen and reducing gaseous losses.

    4. Shoot biomass and nitrogen content

    The PS+WB treatment resulted in the greatest shoot biomass (6,770 kg ha⁻¹), which was significantly higher than the biomass in the PS-only (5,113 kg ha⁻¹) and the water control (3,215 kg ha⁻¹) (Fig. 4A). The PS+WB treatment resulted in the highest crude protein (CP) and total digestible nutrients (TDN) content, indicating improved forage quality (Fig. 4B and C). The enhancement in CP content suggests that plants in the PS+WB treatment exhibited superior nitrogen uptake efficiency.

    Ⅳ. DISCUSSION

    Biochar is has been demonstrated to enhance the water retention capacity of soil, thereby improvinits hydraulic properties, and enabling agricultural soils can to retain more water over extended periods (Liu et al., 2016). In this study, the PS+WB treatment consistently resulted in higher soil water content (Fig. 1). Similarly, Ndede et al. (2022) reported that the biochar derived from wood-based feedstocks significantly increased the water retention capacity. Furthermore, the PS+WB treatment consistently maintained higher total N levels compared to PS-only throughout the experiment (Table 1). The characteristic of biochar such as high cation exchange capacity contributes to the effctie adsorption of NH4+ (Gai et al., 2014), preventing its rapid transformation into NH₃ gas (Hussain et al., 2017). The elevated NH₄⁺-N content in PS+WB further substantiates this finding after day 17 (Table 1), although it underwent a gradual decline due to NH₃ volatilization and nitrification (Beeckman et al., 2018). Interestingly, NO₃⁻-N levels were lower in PS+WB compared to PS-only, suggesting that biochar may have impacted the soil microbial community or decelerated the nitrification process. This observation aligns with the findings reported in previous studies, which demonstrated that biochar application reduced NO₃⁻ leaching by promoting ammonium retention and stabilizing nitrogen transformations in the soil (Gai et al., 2014;Li et al., 2021). These results suggest that wood biochar can help mitigate nitrate leaching and enhance soil nitrogen availability for plant uptake.

    The application of wood biochar significantly induced to a significant reduction in both NH₃ and N₂O emissions compared to the PS-only treatment (Figs. 2 and 3). NH₃ emissions presented a notable increase during the initial 10 days following pig slurry application in PS-only treatment, indicating rapid ammonium volatilization (Fig. 2). In contrast, the PS+WB treatment demonstrated a substantial decrease in both daily and cumulative NH₃ emissions, likely due to the adsorption of NH₄⁺ onto biochar surfaces. This result is consistent with previous studies demonstrating that biochar application limits NH₃ volatilization by enhancing ammonium retention in soil (Huang et al., 2019;Jarosz et al., 2022). Janczak et al. (2017) observed a 30% reduction in cumulative NH3 emissions with the addition of 5% of woodchip biochar in poultry manure, which can be attributed to its stronger adsorption capacity of NH3 gas, with greater porosity and larger surface (Kizito et al., 2015;Ghorbani et al., 2019). Similarly, cumulative N₂O emissions were significantly lower in the PS+WB treatment (Fig. 3). The suppression of N₂O emissions can be attributed to the ability of biochar to alter soil aeration and microbial activity, thereby reducing the denitrification process that leads to N₂O production. Previous research has demonstrated that biochar’s capacity to enhance denitrification, reducing N₂O emissions, has been well documented (Liu et al., 2024). Furthermore, Cayuela et al. (2013) confirmed using 15N stable isotope techniques that biochar mitigates N₂O emission by promoting reduction N₂O to N2 gas during denitrification. In field studies employing meta-analysis, biochar has been shown to potentially reduce N2O emissions by up to 28% (van Zwieten et al., 2010). These findings emphasize the potential of wood biochar as a sustainable strategy to minimize nitrogenous greenhouse gas emissions from pig slurry applications.

    The enhanced soil nitrogen retention and diminished nitrogen losses resulted in higher shoot DM production and better forage quality in the PS+WB treatment (Fig. 4). The significant increase in shoot biomass, CP content, and TDN suggests that wood biochar facilitated greater nitrogen availability for plant uptake. These findings are consistent with previous research that has demonstrated the efficacy of biochar application in enhancing nitrogen retention, delaying nitrogen mineralization, and increasing plant nitrogen uptake efficiency (Kizito et al., 2015; Kumar et al., 2024). Moreover, the enhanced soil moisture content observed in the PS+WB treatment likely contributed to improved plant growth by reducing water stress and maintaining favorable conditions for nutrient absorption.The high porosity and watr retention capacity of wood biochar have been well documented, and the present results further confirmed its ability to enhance soil water-holding capacity, thereby supporting plant productivity.

    Ⅴ. CONCLUSIONS

    The finding results of this study provide substantial evidence that wood biochar application in PS-amended soils contributes an effective strategy for enhacing nitrogen management in agricultural systems. The ability of wood biochar to reduce NH₃ and N₂O emissions, enhance nitrogen retention, and enhance crop productivity has been demonstrated. These observations suggest that its incorporation could facilitate sustainable livestock waste recycling while concurrently reducing environmental impacts. In light of the mounting imperative for sustainable agricultural practices, the integration of biochar into pig slurry management strategies hold considerable potential in mitigating the deleterious effects of nitrogen losses, thereby fostering nutrient-efficient crop production.

    Ⅵ. ACKNOWAGEMENTS

    This work was supported by the National Research Foundation of Republic of Korea (NRF-2022R1C1C2011575).

    Figure

    KGFS-45-1-82_F1.gif

    Changes in soil water content in non-pig slurry (water), pig slurry (PS), and PS combined with wood biochar (PS+WB) during the vegetative growth of Brassica napus over 43 days. The values are presented as mean ± S.E. (n = 3).

    KGFS-45-1-82_F2.gif

    Changes in emission of daily ammonia (NH3, A) and cumulative NH3 in non-pig slurry (water), pig slurry (PS), and PS combined with wood biochar (PS+WB) during the vegetative growth of Brassica napus over 43 days. The values are presented as mean ± S.E. (n = 3).

    KGFS-45-1-82_F3.gif

    Changes in emission of daily nitrous oxide (N2O, A) and cumulative N2O (B) in non-pig slurry (water), pig slurry (PS), and PS combined with wood biochar (PS+WB) during the vegetative growth of Brassica napus over 43 days. The values are presented as mean ± S.E. (n = 3).

    KGFS-45-1-82_F4.gif

    Changes in shoot dry matter (DM, A), crude protein (B), and total digestible nutrients (TDN, C) in non-pig slurry (water), pig slurry (PS), and PS combined with wood biochar (PS+WB) during the vegetative growth of Brassica napus over 43 days. The values are presented as mean ± S.E. (n = 3).

    Table

    Changes in amounts of total N, ammonium-N (NH4+-N), and nitrate-N (NO3--N) in soils from pots treated with non-pig slurry (water), pig slurry (PS), and PS with wood biochar (PS+WB) over 43 days

    The values are presented as mean ± S.E. (n = 3).
    Data with different letters in a vertical column are significantly different at p<0.05 according to Duncan’s multiple range test.

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