Objective Organic nitrogen mineralization process plays crutial role in derterming soil nitrogen supply capacity and crop nitrogen use efficiency. We investigated the effect of common used organic fertilizer sources on the nitrogen mineralization of soil aggregates in yellow mud field, aiming to reveal the regulation mechanism of them on regulating soil nitrogen supply.

Methods The soil samples were collected from the plots subjected to a 36 years of positioning experiment in a yellow mud field. The treatments included: no fertilization control (CK), single application of chemical fertilizer (NPK), chemical fertilizer plus cow dung (NPKM), and chemical fertilizer plus total rice straw returning (NPKS). The wet screening method was used to screen soil aggregate in sizes of >2 mm and 0.25−2 mm. Then the aggregates were incubated in darkness for 161 days, during which the total N, available N, microbial mass nitrogen content were analyzed regularly.

Results Compared with CK, all the NPK, NPKM and NPKS treatments increased the cumulative nitrogen mineralization of soil, the increments in the bulk soil, >2 aggregates, and 0.25−2 mm aggregates by were 10.7%−58.3%, 7.1%−49.4%, and 36.6%−50.1%, respectively. The cumulative nitrogen mineralization of bulk soils and >2 mm aggregates in NPKM and NPKS treatments were significantly higher than that of NPK treatment, and the nitrogen mineralization potential were significantly higher than that under CK and NPK treatment. The nitrogen mineralization potential of >2 mm aggregates under each fertilization treatment was significantly higher than that of 0.25-2 mm aggregates, but the mineralization rate constant, except for NPKS treatment, was the opposite. The nitrogen mineralization accumulation and mineralization potential of all aggregates were positively correlated with total N, alkali-hydrolyzed N, organic carbon and microbial biomass nitrogen (P<0.05), while the nitrogen mineralization accumulation and mineralization potential of undisturbed soil and >2 mm aggregates were negatively correlated with bulk density (P<0.05).

Conclusions Organic nitrogen in >2 mm aggregates is pivotal to soil nitrogen pool, and that in 0.25−2 mm aggregates influences soil nitrogen supply capacity. Long-term combined application of chemical fertilizers with caw manure and straw could significantly enhance the nitrogen mineralization potential of both >2 mm and 0.25−2 mm aggregates in yellow-mud paddy soil by increased nitrogen pools and microbial activity, with cattle manure being more effective than straw. Caw manure also shows effects on steep up the mineralization rate of 0.25−2 mm aggregates, showing higher nitrogen supply capacity than straw. So caw manure and chemical fertilizer is more effective in regulating the accumulation and supply potential of soil nitrogen in the low fertility yellow-mud field.