Study On Nitrogen Mineralization With Biochar Amendment In Lou Soil

Nitrogen is an essential nutrient for crop production. However, nitrogen in agriculture ecosystem is potentially problematic as it can promote environment damage. It will be the key task for the soil research to reduce the nitrogen fertilizer input and to control adverse effects on environment. Biochar additions to soil have been reported to enhance soil fertility whilst simultaneously storing carbon. Biochar application alters soil nitrogen dynamics. Research to date shows that biochar potentially has the ability to manipulate the rates of N cycling in soil systems by influencing nitrification rates and adsorption of ammonia and increasing NH4+ storage by enhancing cation exchange capacity in soils. However, there was no consistent conclusion in terms of soil property variations. In order to assess the effect of biochar on soil nitrogen mineralization and soil physico-chemical properties in Guanzhong Plain soil, biochar made from wheat straw was applied to Lou Soil. The study consisted of two units:(1) a laboratory experiment was conducted to explore the soil nitrogen mineralization affected by three factors(biochar, water and nitrogen fertilizer) using a uniform experimental design and(2) field trial, which has been applied biochar for one crop growth season, was carried out to measure the soil nitrogen supply capacity by determining of total nitrogen and mineralized N characterization of soil nitrogen. Soil bulk density, pH, total organic carbon, available phosphorus, potassium were tested to evaluate the soil quality.The main results were as follows:(1) Chemical nitrogen fertilizer increased soil inorganic nitrogen accumulation. Among three types of nitrogen fertilizer, ammonium nitrogen fertilizer showed more influence on inorganic nitrogen accumulation than nitrate fertilizer and amide nitrogen fertilizer.(2) Soil pH revealed a significant change in the early stage of fertilization, i.e., a slight decrease was found in first one week when applied ammonium nitrogen and amide nitrogen fertilizer, then followed by a rise. This effect was strengthened with the application of biochar.(3) The partial least squares regression analysis demonstrated that first two of the three independent variables(nitrogen, water, biochar) response to independent variable(soil pH value, NH4+-N, NO3--N, Nin content) accounted for 81.8% to 86.7%. Respectively, nitrogen fertilizer and biochar had a negative effect on changes in soil pH value while water played a positive effect(except nitrate fertilizer was negative). For the NH4+-N changes, negative effect were found in nitrogen fertilizer(except nitrate fertilizer was positive) and bicohar. For the NO3--N changes, positive effect were found in nitrogen fertilizer and biochar(except ammonium fertilizer was negative), while water had a negative effect. In summary, biochar played a quite weak role on soil nitrogen mineralization processes compared with the nitrogen fertilizer and soil moisture. However, biochar did promote nitrification in the early stage of fertilization.(4) The field soil mineral nitrogen characteristics illustrated that soil nitrogen supply capacity significantly increased with the application of nitrogen fertilizer and the irrigation. The biochar combined with nitrogen fertilizer treatment showed a slight improvement of soil nitrogen supply capacity than nitrogen fertilizer treatment. However, the double amount of biochar addition even had no significant difference compared with the control.(5) The application of biochar significantly affect the physic-chemical properties of soil, i.e., the highest biochar application rate(8 t/ha) failed to significantly reduce soil bulk density, but increased the soil organic carbon. Soil pH value decreased with the biochar application rate increasing. Biochar amendment lessened the residual nitrate and elevated ammonium in soil. Soil available phosphorus increased by 19.7% ~ 142.4%, but only the 8 t/ha application rate reached the significant level. Biochar additions significantly increased soil available potassium by 29.2% to 149%.We concluded that biochar affected the nitrogen mineralization by promoting nitrification in the early stage of fertilization. Changes in soil physico-chemical properties influenced by biochar were strongly depended on biochar application rates.