Long-term application of manures plus chemical fertilizers sustained high rice yield and improved soil chemical and bacterial properties

Compared to the short-term experiment, we have a lack of understanding about the long-term effect of fertilizers on rice yield and paddy soil properties under the conditions of frequent soil disturbance and intensive cropping cultivation. Thus, a 32-year (1984-2015) field experiment was established on a red clay soil (typical Ultisols) near Nanchang, Jiangxi province, China, to assess the effects of inorganic and organic fertilizers on rice yields, soil chemical properties and bacterial communities in early rice-late rice-Astragalus sinicus L. rotation system. Manure applications in combination with different proportions of chemical fertilizer in terms of nitrogen, particularly 70 M + 30CF (70% manure in combination with 30% chemical fertilizer), sustained high rice yields and increased soil OM, 1 N NaOH-hydrolyzed N, Olsen phosphorus, microbial biomass, and bacterial diversity but alleviated soil acidification. The soil receiving MCF had a great number of bacterial operational taxonomic units and high richness indexes. Compositions and abundances of predominant bacteria in soils varied among the fertilizer treatments and all of bacterial communities were dominated by three major phyla (Chloroflexi, Proteobacteria, and Acidobacteria), which were more than 70% of the total sequences in each of the soils examined. Among the top 15 predominant bacteria, seven were commonly found in all studied soils and only 1-2 phylotypes were unique in each soil. A large number of facultative anaerobic and aerobic bacteria, including Thiobacillus thioparus, Bradyrhizobium, and Nitrospira, were present in all studied soil. Therefore, bacterial community compositions can reflect soil processes such as acidification, greenhouse gas emission and nitrogen recycling in response to tillage and fertilizer managements.