Effect Of Nitrogen Fertilizer And Biochar On Microbial Activity And Ammonia Oxidation In Soils

Since 1980s, the application of a large amount of nitrogen fertilizer has brought serious environmental negative effect. In recent years, biochar is a kind of functional material has been applied in agricultural production, which can effectively improve the living environment of soil microorganisms. Microorganism is an important component of soil ecosystem, soil microbial activity and enzyme activity are important indicators of soil quality, ammonia oxidizing bacteria (AOB) and ammonia oxidizing bacteria (AOA) are significant roles in the nitrification of nitrogen. Therefore, the study based on the soil microorganism, and was combined with the long-term fertilizer experiment and indoor culture experiments. The calculation of physical chemical and biological methods, the microcalorimetry and real-time fluorescent quantitative PCR technology are applied to study the change of soil microbial activity and enzyme activity in soil wheat maize rotation systems in the North China Plain. The AOB and AOA functional gene amoA copy numbers were quantitatively analyzed when the soil microbial activity and enzyme activity are higher, and then the effect of the application of biochar on the soil microbial biomass of two types (acid and alkaline soil) was further analyzed.The main research results are as follows:(1) Different nitrogen application rate has significant effect on soil microbial activity and enzyme activity of soil, and the soil microbial activity and enzyme activity in different growth stages were different. The soil microbial activity of non and high nitrogen treatments were lower than that of other nitrogen fertilizer treatments. The optimal amount of nitrogen fertilizer (wheat soil≤250 kg hm-2, maize soil≤210 kg hm-2) can improve soil microbial activity, but would be inhibited when the application rate is over the range. (2) Soil enzyme activity is up to the highest value when the crop in vigorous growth period. The effects of different nitrogen fertilizer content on soil enzyme activities were different due to different types of enzymes. The soil enzyme index of 250 kg hm-2 was higher in wheat soil and the soil enzyme index of 210 kg hm-2 was higher in maize soil. (3) The study of functional genes and diversity indices showed that the copy number of functional genes amo A of AOB and nitrification potential increased with the increase of nitrogen application rate, while the copy number of functional genes amoA of AOA decreased, the ratio of AOA and AOB is more than 1, which indicated that the AOB and AOA in the region occupied an important position in the process of ammonia oxidation. But the contribution of the former is relatively large. (4) The indoor experiment of the application of biochar can reduce the effects of excessive nitrogen application rate, and can stimulate the growth of soil microorganisms.To sum up, the relationship between soil microorganisms and different nitrogen application rate plays an important role on reflecting soil environment. The application of biochar can reduce the effect that the change of soil pH, microbial activity, enzyme activity and ammonia oxidizing microorganism due to excessive nitrogen fertilizer on the soil.