[Effects of straw returning amount and type on soil nitrogen and its composition]

By field experiment and cultivation simulating, we analyzed the impacts of oilseed rape straw incorporation on root, tiller and grain yield of rice. Results showed that straw incorporation treatments decreased 1-2 in tillers and 1.0-8.6 mg per plant in bleeding sap. The activities of glutamine synthetase (GS), glutamic-pyruvic transaminase (GPT) and glutamic-oxalacetic transa-minase (GOT) of root in straw incorporation treatments were reduced by 0.10-6.11, 0.06-0.31 and 0.52-0.84 μmol·g^-1·h^-1 respectively as compared to control, during the earlier stage (0-36 d after transplanting) of rice growth. Compared to no straw incorporation treatment, the straw incorporation by plough method increased bleeding sap by 3.4-11.7 mg per plant, and increased the activities of GS, GPT and GOT by 0.34-0.78, 0.13-0.45 and 0.18-0.20 μmol·g^-1·h^-1 respectively. During the later stage (56 d after transplanting) of rice growth, straw incorporation treatments by mulching reduced bleeding sap by 19-25 mg per plant, and increased the activities of GS, GPT and GOT in root by 0.16-0.34, 0.08-0.21 and 0.06-0.32 μmol·g^-1·h^-1, respectively. The grain yield of total straw returning treatments (MF₂ and FH₂) were higher than other straw returning treatments. In comparison of MF₂, the rice yield of FH₂ was higher by 0.13-0.48 t·hm^-2. Oil seed rape straw incorporation hindered rice root growth and delayed the reviving of rice after transplanting, by decreasing the activities of roots and nitrogen metabolizing enzymes during earlier stage. However, it promoted rice root growth by increasing activities of roots and nitrogen metabolizing enzyme during media and later stage. The increase or decrease of rice yield is a comprehensive balance of multiple factors in straw incorporation rice field. Total straw incorporation by plough method is one of the better straw returning manners for oilseed rape-rice rotation system in Sichuan Basin area.