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Highlights • Interactions between biochar and N affected N availability and SIN leaching. • Overuse of biochar reduced the SIN available for both crops and leaching. • Field-aged biochar captured NO 3 −-N and sequestered it in the soil. • Biochar reduced the residual NO 3 −-N available for leaching. Abstract Biochar has been proposed to ameliorate soil properties and plant growth. However, it remains unclear how the interaction between biochar and nitrogen (N) fertilizer impacts soil inorganic nitrogen (SIN) leaching and availability in dryland systems. Therefore, a two-year field experiment was carried out on the Loess Plateau in northern China to study the effects of biochar combined with N fertilizer on the leaching and availability of SIN. Biochar applied at 0, 20 and 40 t ha−1 (B0, B1 and B2, respectively) interacted with three N fertilization levels (0, 120 and 240 kg N ha−1; N0, N1 and N2, respectively). Winter wheat (Triticum aestivum L.) was cultivated in a winter wheat-summer fallow cropping system. We measured wheat aboveground biomass and residual SIN in the soil profile (0–60 cm at 10 cm intervals) using standard extraction methods (2 M KCL, shaking at 25 °C for 1 h). Additionally, to ascertain whether field-aged biochar captured SIN and to determine residual SIN availability, we also used a modified extraction method (2 M KCL, shaking at 60 °C for 2 h) and ion exchange membranes (IEMs) to extract SIN from plow layer soil (0–20 cm). Our results indicated that biochar application alone in the absence of N fertilization had no significant effect on wheat biomass or residual SIN in the soil profile. However, compared with the application of N fertilizer alone, the application of biochar at 20 t ha-1 combined with N fertilizer not only increased wheat biomass by 12.2–13.8% but also significantly decreased residual NO 3 −-N in the subsoil by 13.2–74.7%. Nevertheless, long-term N fertilization at 240 kg N ha-1 led to large amounts of residual NO 3 −-N without a significant increase in crop biomass, which inevitably increased the risk of leaching during the fallow period. Although the application of biochar at 40 t ha-1 combined with N fertilizer more effectively decreased residual SIN in the subsoil, this approach was impractical because it decreased wheat biomass. Furthermore, the difference between NO 3 −-N extracted via the modified method and via the standard method increased with biochar application under each N level. Thus, field-aged biochar absorbed a certain amount of NO 3 −-N, thereby sequestering N in the soil after two years of N fertilization. Hence, biochar could reduce the residual NO 3 −-N available for leaching during the fallow period. However, notably, overuse of biochar could reduce the amount of NO 3 −-N available not only for leaching but also for crops. Ultimately, the application of biochar at 20 t ha-1 combined with N fertilization at 120 kg N ha-1 is a promising dual-win strategy for improving N availability while concurrently mitigating SIN leaching. [ABSTRACT FROM AUTHOR]

Biochar is anticipated to be an effective option for mitigating nitrogen (N) leaching and improving the hydraulic characteristics of soil, particularly sandy soil. However, little attention has been paid to understanding the effect of biochar on N leaching and hydraulic conductivity ( K ) in fine-textured soil. Additionally, whether different biochar application methods have different effects on N leaching and K remains unclear. Therefore, our objective in this study is to determine the effects of biochar with different application methods on nitrate/ammonium leaching and K in silty clay soil. The three biochar application patterns were as follows: A, biochar was mixed into 0–10 cm of surface soil; B, biochar was mixed into 10–20 cm of subsurface soil; and C, biochar was mixed evenly into 0–20 cm of plow layer soil. In addition, biochar was added at three rates, namely, 1%, 2% and 4% (mass ratios), and a soil column without biochar addition served as the control (CK). Our results demonstrated that the choice of biochar application method significantly influenced N leaching and soil K and balance between the soil K and N leaching, particularly for nitrate. Additionally, the leaching of N in silty clay soil occurred mainly in nitrate form. Compared with the CK, all 1% biochar treatments increased nitrate leaching (except C1%, which showed no differences from the CK) and tended to decrease K. However, all 4% biochar treatments increased nitrate leaching due to a high K . All 2% biochar treatments significantly reduced nitrate leaching by 8.3–17.0%, and B2% significantly increased the saturated hydraulic conductivity ( K sat ) of soil by 20.9%. Hence, the mixing of biochar at a rate of 2% into the subsurface soil effectively mitigated N leaching and increased K in silty clay soil. These findings could have some implications for the field application of biochar. For instance, the combination of subsurface biochar application with that of fertilizer to roots in orchards or with deep tillage in fields, which would mimic the B2% model, would yield multiple benefits, including lower costs. [ABSTRACT FROM AUTHOR]

Purpose: The agriculture industry is under intense pressure to produce more food with a lower environmental impact, while also mitigating climate change. Biochar has the potential to improve food security while improving soil fertility and sequestering carbon. The aim of our research was to evaluate the effects of apple branch biochar on wheat yield and soil nutrients under different nitrogen (N) and water conditions.Materials and methods: Durum wheat was grown for nearly 6 months in pots with silt clay soil supplemented with apple branch biochar. The biochar was applied at five rates (0, 1, 2, 4, and 6% w/w; B0, B1, B2, B3, and B4), and N fertilizer was applied at three rates (0, 0.2, and 0.4 g kg−1; N0, N1, and N2). From the jointing to maturation stages, the soil water content was controlled at two rates to simulate sufficient water and drought conditions (75 and 45% of field capacity; W1 and W2). After harvest, we investigated grain yield and soil nutrient status.Results and discussion: The application of biochar alone had a positive effect on wheat production and soil nutrients, especially under sufficient water conditions. Compared with the addition of N fertilizer alone, the addition of biochar at B1 and B2 combined with N fertilizer under sufficient water conditions increased the crop yield by 7.40 to 12.00%, whereas this was not the case under drought stress. Furthermore, regardless of water conditions, compared with N fertilizer application alone, a high rate of biochar application (B3 and B4) led to a significant decrease in the grain yield of approximately 6.25-21.83%. Biochar had strong effects on soil nutrients, with NO3− and available phosphorus contents and the C:N ratio exerting the greatest effects on wheat yield.Conclusions: The effects of biochar on wheat production and soil nutrients varied with the biochar application rate, N fertilizer application rate, and water conditions. Drought stress weakened or offset the positive effect of biochar on crop production, especially under the high-N level (N2) conditions. The optimum application combination was 1% (or possibly even less) apple branch biochar (B1) and moderate N fertilizer (N1). [ABSTRACT FROM AUTHOR]

The incorporation of biochar into soil has been proposed as a strategy for enhancing soil fertility and crop productivity. However, there is limited information regarding the responses of soil respiration and the C, N and P cycles to the addition of apple branch biochar at different rates to soil with different levels of N. A 108-day incubation experiment was conducted to investigate the effects of the rate of biochar addition (0, 1, 2 and 4% by mass) on soil respiration and nutrients and the activities of enzymes involved in C, N and P cycling under two levels of N. Our results showed that the application of apple branch biochar at rates of 2% and 4% increased the C-mineralization rate, while biochar amendment at 1% decreased the C-mineralization rate, regardless of the N level. The soil organic C and microbial biomass C and P contents increased as the rate of biochar addition was increased to 2%. The biochar had negative effects on β-glucosidase, N -acetyl-β-glucosaminidase and urease activity in N-poor soil but exerted a positive effect on all of these factors in N-rich soil. Alkaline phosphatase activity increased with an increase in the rate of biochar addition, but the available P contents after all biochar addition treatments were lower than those obtained in the treatments without biochar. Biochar application at rates of 2% and 4% reduced the soil nitrate content, particularly in N-rich soil. Thus, apple branch biochar has the potential to sequester C and improve soil fertility, but the responses of soil C mineralization and nutrient cycling depend on the rate of addition and soil N levels. [ABSTRACT FROM AUTHOR]

• The effect of biochar application depth on soil CO 2 and CH 4 fluxes was examined. • Soil respiration and CH 4 uptake highly depend on the soil environment at 0–10 cm. • Biochar incorporation into the 10–20 cm depth promoted soil C sequestration. The remarkable soil carbon sequestration and greenhouse gas mitigation effects of biochar have spurred great interest in exploring ways to maximize its benefits. However, it remains unclear how biochar application depth impacts soil carbon dioxide (CO 2) emissions and methane (CH 4) uptake in upland soil. Therefore, we carried out a 16-month field experiment in a dryland agricultural system to answer the above questions. Woody biochar (20 t ha−1) was mixed into three soil layers: 0–10 cm (BC 0-10cm), 10–20 cm (BC 10-20cm), and 0–20 cm (BC 0-20cm). Soil without biochar addition was used as the control (CK). We monitored soil CO 2 and CH 4 fluxes continuously and determined the metabolic quotient (qCO 2) and the sensitivity of soil respiration to temperature (Q 10). The results indicated that CO 2 emissions, CH 4 uptake, qCO 2 and Q 10 were significantly affected by biochar application depth. Overall, compared with CK, BC 0-10cm increased total CO 2 emissions by 10.13%, while BC 10-20cm and BC 0-20cm showed no significant effect. BC 0-10cm and BC 0-20cm exhibited greater soil CH 4 uptake enhancement than BC 10-20cm , but the enhanced CH 4 uptake resulted in limited net greenhouse gas mitigation. BC 10-20cm and BC 0-20cm had a lower qCO 2 than the other treatments, which likely increased the carbon use efficiency and decreased the stress on soil microbes, but BC 0-10cm showed the opposite effect. In addition, BC 0-10cm significantly reduced Q 10 mainly due to the enhanced lability of the native carbon and microbial activities. Changes in environmental factors in the 0–10 cm soil largely explained the variations in CO 2 emissions, CH 4 uptake and Q 10 (>88%). Nevertheless, the enhanced microbial biomass in the 10–20 cm soil helped lower qCO 2 in the whole 0–20 cm layer. In summary, adding biochar to surface soil (0–10 cm) likely accelerates carbon loss, due to the strong shift in the environment of the surface soil caused by complex interactions among hydrothermal conditions, nutrient levels (i.e., N, NH 4 +, NO 3 − and available P) and labile carbon. However, adding biochar to subsurface soil (10–20 cm) can effectively avoid severe disturbance of the surface soil environment and thus benefit soil carbon sequestration in the long term. [ABSTRACT FROM AUTHOR]