[Effects of consecutive application of composted sewage sludge on active organic nitrogen fractions in the sandy fluvo-aquic soil.].

A field experiment was conducted with sandy fluvo-aquic soil under wheat-maize rotation system during 2012 to 2016 in Henan Province, with four treatments: Chemical fertilizer (CK), composted sewage sludge (CS) 15 t·hm(CS), 30 t·hm(CS), 45 t·hm(CS). We investigated the effects of CS on soil active organic nitrogen and its allocation ratio. Results showed that CS significantly enhanced soil water content, decreased soil pH, increased contents of soil organic carbon and total nitrogen (TN) and available nutrients. Soil TN was increased by 93.1%-284.3%. The CS treatment significantly improved the content of light fraction organic nitrogen (LFON), particulate organic nitrogen (PON) and microbial biomass nitrogen (MBN). CS treatments promoted the allocation of PON/TN and MBN/TN. with an enhancement of 12.3% and 539.9% in the CS treatment, respectively. The distributions of LFON/TN and DON/TN were decreased by 17.3%-40.1% and 38.5%-71.3%, respectively. The contribution of soil active organic nitrogen fractions to TN was: PON>LFON>DON>MBN. Results from the principal component analysis showed that organic nitrogen and their distribution had high load value in CS and CS treatments. Results from redundancy analysis showed that positive correlations existed between the soil physicochemistry, enzymatic activity and soil active organic nitrogen as well as their distribution. In summary, CS had positive impacts on soil organic matter, soil properties, and the formation of active organic nitrogen. The rates of 30 and 45 t·hm CS application had significant effects on soil fertility, which could be an effective way to improve sandy fluvo-aquic soil quality.