关键词: 稻田, 秸秆还田, 施氮量, 氮肥基追比, 微生物量碳氮, 水溶性有机碳氮

Abstract:

【Objective】Soil microbial biomass carbon & nitrogen (N) (SMBC & SMBN) and water soluble organic carbon & nitrogen (DOC & DON) are the active pools in soil, which are essential indexes for assessing soil carbon and nitrogen turnover and nutrient availability for providing scientific information and guidelines and nitrogen management under straw returning in rice-wheat rotation system. The objective of the study was to investigate the effects of straw incorporation, nitrogen application rate and basal/topdressing ratios of nitrogen fertilizers on the SMBC, SMBN, DOC, DON, ROC and AN at paddy field, so as to explicit the optimal nitrogen rate and basal/topdressing ratios of nitrogen fertilizers under the straw incorporation condition. 【Method】A 4-year field experiment with straw incorporation matched with nitrogen fertilizer was conducted in rice cropping system from 2012 to 2015 in Jingmen city, Hubei Province. Three field experiments including different nitrogen application, straw incorporation combined with nitrogen fertilization and different ratios of base N to dressing N. Field experiments included: (1) different nitrogen rates, including No N fertilizer (N0), Optimal N fertilizer (165 kg N·hm ^-2, N165), the farmer common N rate (195 kg N·hm ^-2, N195); (2) different straw incorporation combined with nitrogen fertilization: straw removal (CK), straw incorporation (wheat straw incorporation before rice transplanting, S), straw incorporation matched with farmer common N rate (SN), straw incorporation matched with optimal N rate (SF), SF plus straw decomposing microbial inoculants (SM); (3) three basal/topdressing ratios of nitrogen fertilizers in the shooting and heading stage: 7﹕3﹕0 (R1), 5﹕3﹕2 (R2); 10﹕0﹕0 (R3). 【Result】The results showed that the SMBC content significantly increased at rice jointing stage and the DOC content obviously decreased after the maturity under the SN treatment. The DON content increased under the SF treatment at rice jointing stage. DON and ROC contents decreased under the SM treatments at the maturity and jointing stage. The AN content increased in the SF treatment at rice heading and grain filling stage. Appropriate N application rate (165 kg N·hm ^-2) was favorable to increasing the DON and AN in soil. However, the DON and AN contents decreased under high application rate of N fertilizer (195 kg N·hm ^-2). The higher proportion of topdressing fertilizer increased the SMBN and ROC contents at rice jointing stage, but had no impacts on the SMBC and DOC contents. 【Conclusion】Nitrogen rate and basal/topdressing ratios were main factor for determining active soil carbon and nitrogen contents under straw incorporation in Paddy field. Appropriate nitrogen fertilizer could increase SMBC, AN, and DON contents, and the higher topdressing fertilizer could also increase active soil carbon and nitrogen contents during rice growth stage.

Key words: paddy field, straw incorporation, nitrogen application rate, basal/topdressing ratios of nitrogen fertilizers, soil microbial biomass carbon/nitrogen (SMBC/SMBN), water soluble organic carbon/nitrogen (DOC/DON)