Dynamic and migration characteristics of soil free amino acids during the whole growth period of rice after application of milk vetch

Abstract

Abstract. Free amino acids (FAAs) in soil play an important role in the soil nitrogen cycle and plant nutrition. However, the attributing factors and migration characteristics of free amino acid pools in paddy soils after green manure application during the entire growth period of rice have not been elucidated. In this study, a single application of chemical fertilizer (CK) was used as a control under equal nitrogen, phosphorus and potassium conditions, and different application rates of milk vetch (15 000 kghm−2(CL), 30 000 kghm−2(CM) and 45 000 kg hm−2(CH)) were selected to investigate the dynamic of FAAs concentration and composition in paddy soil. Soil FAAs concentration at different growth stages under the same fertilization treatments was highest at the seedling stage and lowest at the tillering stage. The concentration of threonine, alanine, valine, isoleucine, leucine, phenylalanine was most abundant under different fertilization treatments during the growth period, accounting for 59.42 %–76.46 % of the respective FAAs pool. The application of milk vetch was shown to increase the soil FAAs concentration, especially glutamic acid, which increased by 368.17 %–680.78 %, but excessive application had an inhibitory effect. Soil pH, organic matter, protease, bacterial biomass and community were critical factors affecting the concentration of soil FAAs. Bacteroidetes, Firmicutes and Nitrospirae significantly affected the dynamics of FAAs in bacterial communities, and their total contribution rate was 56.89 %. FAAs displayed significant vertical profile characteristics, and the mobility of serine, glycine and proline was high. Conclusively, the application of milk vetch was able to significantly change the concentration and composition of soil FAAs, which may affect the capture of N by plants.