Study On Controlled Effect Of Biochar To The Soil Nitrogen In Greenhouse Vegetable Soils

Nitrogen is an essential nutrient element required for plant growth and development. Nitrogen fertilizing has become an important means of improving grain yield in the last decades. Nitrogen in the soil transfers to the atmosphere, the soil and the water through volatilization, leaching and overland runoff, and thus brings a great influence to the farmland environment and people’s production and living. Therefore, the reduction of the leaching loss of nitrogen from the soil plays a positive role in the improvement of the utilization of fertilizer in the soil and agroecological environment.Peanut shells were selected as material and pyrolyzed (300℃) under low-oxygen condition to prepare the biochar. The characteristics of NH4+-N adsorption of the biochar derived from peanut shells were studied with concentration gradient method, and the adsorption mechanism and its influence factors were also discussed from the point of view of thermodynamics and dynamics. The effect of applying nitrogen-enriched biochar in moist soil on the soil fertility and the microbial functional diversity was investigated through analysis of the physical and chemical properties of soil and Biolog plate assay in a pot experiment. The results are as follows:1. Absorption of ammonium-n onto peanut shell biocharThe results showed that with increase of the initial concentration of NH4+-N in solution, the absorptive amount of peanut sheli biochar to NH4+-N also increased. And when the initial concentration was approximately 500 mg·L-1, the absorption was approaching equilibrium. In the normal condition (25℃, pH=7±0.3), the maximum absorption value was 25.47 mg/g. The Langmuir and Freundlich equation both can achieve good fitting data on the isothermal adsorption of peanut shell biochar to NH4+-N, but Langmuir equation achieved higher regression coefficient, which is more suitable for fitting this isothermal adsorption behavior. It indicates that this absorption is primarily based on single-layer absorption, companied with a certain amount of multi-layer absorption. The absorption of peanut shell biochar to NH4+-N achieved absorption equilibrium at about 30 min. Pseudo second order kinetics equation can well describe the absorptive dynamics of NH4+-N on the surface of peanut shell biochar; as the dosage of peanut shell biochar increased, its absorption to NH4+-N decreased. In the absorption system with initial NH4+-N concentration of 100 mg/L, its appropriate dosage was 12g/L, and the maximum absorption ratio was 40%. The absorption ability of biochar to NH4+-N increased with the increase of pH value of solution. When pH=6-8, the absorption amount increased and stayed stably at a higher level. When pH>8, the absorption amount was highly increased. These results show that the initial concentration of NH4+-N, the dosage of biochar and the pH value of absorptive system are the main factors affecting the absorptive properties of biochar.2. Biotoxicity effect of the biocharThe biochar matrix promoted the germination, rooting, sprout and biomass growth of wheat; liquid extract of the biochar significantly inhibited the germination of wheat, while promoted the growth of the root and the bud of wheat; liquid extract of the soil significantly inhibited the growth and the development of wheat.3. Effect of nitrogen-enriched biochar on the physical and chemical properties of the soilThe physical and chemical properties of soil fertilized with the biochar were better than that fertilized with only nitrogenous fertilizers, and significantly better than that fertilized with neither biochar nor nitrogenous fertilizers.4. Effect of nitrogen-enriched biochar on soil microbial functional diversityAmong soils treated with different biochar applying measures, the AWCD value in the soil treated with C2 (nitrogenous fertilizers only) was the highest, and its microbial community had the most effective carbon substrate utilization than the others. The AWCD values in the soil treated with C4 (6.6g biochar mixed with lkg nitrogenous fertilizers) and C6 (13.3g biochar mixed with lkg nitrogenous fertilizers) were the lowest, indicating that its microbial community had the lowest metabolic activity and the weakest carbon substrate utilization. The soil treated with C3 (3.3g biochar mixed with lkg nitrogenous fertilizers) had a relatively higher activity. In general, applying biochar reduced soil microbial diversity, and dispersed the dominant population, and it’s not good for the maintenance of soil microbial diversity. Applying biochar significantly influenced the metabolic activity of soil microorganisms and the functional diversity of soil microbial community.