Effect of long-term application of manure and mineral fertilizers on nitrogen mineralization and microbial biomass in paddy soil during rice growth stages

Net N mineralization rate (NMR), net N consumption rate (NCR), microbial biomass carbon (MBC) and nitrogen (MBN), potentially mineralizable N (PMN) and mineral N (N-NH4 + and N-NO3 –) were measured in paddy soil at five growth stages of rice to determine the effect of long-term fertilization in subtropical China. The studied long-term treatments included CK (no fertilization), N, NP, NPK and NPK + OM (NPK plus organic manure). The NPK + OM treatment gave the highest values of the measured variables among all treatments. There was no significant difference in other treatments except for mineral N and PMN at early growth stages. All these variables were generally highest at transplanting stage as two thirds of fertilization was applied as basal fertilizers and the rice uptake was low. Then they decreased or leveled off with the rice growth stages except for MN in all treatments. Stepwise regression revealed that NMR was significantly correlated with MBC and N-NH4 + (R2 = 0.954, P < 0.01) at all rice growth stages. So, mineral plus manure fertilizer application and more mineral fertilizer as topdressing were recommended in subtropical paddy soil.