Microbial carbon source utilization in rice rhizosphere and nonrhizosphere soils with short-term manure N input rate in paddy field

Carbon (C) plays a vital role in regulating soil nutrient cycling and increasing soil microbial community, but there is still limited information on how C source utilization characteristics responds to soil physical and chemical properties changes under double-cropping rice (Oryza sativa L.) paddy field in southern China. Therefore, the effects of different short-term manure nitrogen (N) input rate managements on C source utilization characteristics in rice rhizosphere and non-rhizosphere soils under double-cropping rice field in southern China were studied by using 18O-H2O method. Therefore, a field experiment were established in Ningxiang city of Hunan Province, and five different fertilizer treatments were applied: (1) 100% N of chemical fertilizer (M0), (2) 30% N of organic manure and 70% N of chemical fertilizer (M30), (3) 50% N of organic manure and 50% N of chemical fertilizer (M50), (4) 100% N of organic manure (M100), and (5) without N fertilizer input as control (CK). The results showed that soil microbial biomass C content, soil microbial growth rate, and soil microbial basal respiration with application of organic manure treatments (M30, M50, M100) were significantly higher (p < 0.05) than that of CK treatment. And the soil C utilization efficiency with M0 treatment were significantly higher (p < 0.05) than that of M100 treatment. Compared with CK and M0 treatments, the metabolic capacity of soil microorganisms to exogenous C sources with M30, M50 and M100 treatments were increased. The largest types of exogenous C source was carboxylic acids, followed by amino acid and carbohydrate, and complex compounds was the smallest. The RDA analysis results indicated that fertilizer treatments significantly changed the utilization characteristics of soil microorganisms to exogenous C sources. As a result, this study found that characteristics of soil C source utilization were significantly affected by different short-term manure N input rate managements.