Study On Controlled Effect And Mechanism Of Biochar To The Soil Nitrate In Greenhouse Vegetable Soils

Aiming at the adsorption characteristics of biochar, soil N leaching restricting agricultural develop-ment, the diversity of soil microbial community and other problems, this paper preliminarily discussed the relevant problems through preparing biochar by taking peanut shells as raw materials. The main research results are as follows:(1) Peanut shell was used as raw material to prepare biochar through low-oxygen pyrolysis(300?).FTIR and XPS spectra were used to analyze the biochar before and after batch equilib-rium adsorption test to explore the biochar absorption mechanism of nitrate (NO3--N). The results showed that biochar adsorption of NO3--N significantly affected by the pH value.Accompanied with the increase of initial concentration of NO3--N solution, the adsorption quantity of biochar increases gradually, in the adsorption system with the initial concentration of 800 mg·L-1, the maximum adsorption capacity was 40 mg·g-1, Freundlich equation could well fitted (R2= 0.975) to the NO3--N isothermal adsorption process of biochar.The adsorption was non-uniform multilayer adsorption; adsorption of biochar to NO3--N could reach the equilibrium in 30 min, pseudo secondary dynamic equation could effectively describe the process of adsorption kinetics, indicated that the adsorption was mainly chemical adsorption. FTIR and XPS spec-tra analysis show that the functional groups such as hydroxyl (-OH), aromatic ring carbonyl (-C= O) and aliphatic ether (-o-),which distributed on the surface of biochar,were involved in the adsorption proc-ess,and the binding energy of C atoms connected to those functional groups increased. Considering the metal ion distribution on the biochar surface,it demonstrates that formation of hydrogen bond and metallic bond are the main chemical adsorption mechanism of biochar to NO3--N. (2) The test adopted simulating soil column leaching method and studied the biochar's impact on the soil leachate volume, soil pH value, the leaching amount of ammonia nitrogen and nitrate nitrogen, and the growth of Chinese cabbage. The results showed that adding biochar improved the volume of soil column leachate and increased soil's water content and pH value. Compared with the control group, adding biochar reduced 35.9%-65.3% of the ac-cumulated leaching amount of NO3--N, and if the adding amount is bigger, the loss proportion of reducing nitrate nitrogen will be higher; It has no significant difference for the accumulated leaching amount of soil column NH4+-N. Adding biochar didn't increase the crops' growth, and it may be because the growth pe-riod of Chinese cabbage selected by the experiment is short. The test results show that adding peanut shells biochar containing nitrogen to soil column can reduce the loss of nitrogen and increase the immobilization of nitrogen in the soil, but its the influence on the crops'growth needs to be further studied. (3) It adopted DGGE-cloning sequencing technology to study the changes of soil bacterial diversity after adding biochar, and found that adding a big amount of biochar (1%) can promote the increase of Acidobacteria, Phylum Gracilicutes and other bacteria, for example, the Shannon-wiener index of soil bacteria increased by 26%, and evenness index increased by 3.1%; As the decrease of adding amount of biochar, the Shannon-wiener index and evenness index of soil bacteria reduced, so the diversity of soil bacteria is affected by the adding amount of biochar.