Effects of long-term fertilizer practices on rhizosphere soil nitrogen mineralization in the double-cropping rice field

Nitrogen (N) was an important indictor in change of soil fertility, which was closely related with N mineralization process. However, there is still need to further study on how rhizosphere soil N mineralization in paddy field response to different fertilizer management. Therefore, the influence of long-term (37-years) fertilizer regime on rhizosphere soil N mineralization, ammonification and nitrification rates, and its relationship under the double-cropping paddy field in southern of China were investigated in this study. The field experiment included following fertilizer regimes: inorganic fertilizer alone (MF), rice straw and inorganic fertilizer (RF), 30% organic manure and 70% inorganic fertilizer (OM), and no application of any fertilizer as a control (CK). The result indicated that rhizosphere soil organic carbon (SOC), total N, NO3-N, and NH4-N contents in paddy field with OM and RF treatments were increased. The result showed that rhizosphere soil NO2--N and mineral N contents with OM and RF treatments were increased, and the order of soil NO2--N and mineral N contents with all fertilizer treatments was showed as OM > RF > MF > CK. This result proved that soil aerobic and anaerobic N mineralization rates in paddy field with OM and RF treatments were higher than that of CK and MF treatments. Compared with MF treatment, soil ammonification rate with RF and OM treatments increased by 45.16% and 67.74%, soil nitrification rate with RF and OM treatments increased by 45.71% and 77.14%, respectively. There had significantly positively correlation between soil net mineralization, nitrification rate and SOC, total N contents. As a result, applied with rice straw and organic manure was a good measure to improve soil N mineralization in the double-cropping rice field.