秸秆还田配施氮肥对稻田土壤活性碳氮动态变化的影响

Nitrogen Fertilizer and Its Combination with Straw Affect Soil Labile Carbon and Nitrogen Fractions in Paddy Fields

【目的】土壤微生物量碳氮和水溶性有机碳氮是土壤中最活跃的碳氮组分,是衡量土壤碳氮周转与养分有效性的重要指标。探讨秸秆配施氮肥、氮肥用量及基追比例对稻田土壤微生物量碳氮、水溶性有机碳氮、易氧化有机碳和速效氮的影响,明确秸秆还田条件下水稻生长季不同氮肥用量与基追比的土壤活性碳氮变化特征,为稻麦轮作区秸秆还田的氮肥管理提供理论依据。【方法】2012—2015年在湖北省荆门市田间试验中设置施氮量、秸秆配施氮肥和施氮时期3个大田试验。施氮量:不施氮(N0),推荐施氮(165 kg·hm^-2,N165),习惯施氮(195 kg·hm^-2,N195);秸秆配施氮肥:秸秆移除(CK),秸秆还田(移栽前将上季小麦秸秆全部还田,S),秸秆还田+习惯施氮量(SN),秸秆还田+推荐施氮量(SF),秸秆还田+推荐施氮量+腐解菌剂(SM);施氮时期:基施﹕拔节期﹕抽穗期氮肥施用比例为7﹕3﹕0(R1),5﹕3﹕2(R2),10﹕0﹕0(R3)。【结果】秸秆还田+习惯施氮量(SN)显著提高了水稻拔节期土壤微生物量碳(SMBC)含量,但是其成熟期水溶性有机碳含量(DOC)显著降低。秸秆还田+推荐施氮量(SF)显著提高了水稻拔节期土壤水溶性有机氮含量(DON)。腐解菌剂的施用显著降低了水稻成熟期DON含量,拔节期易氧化有机碳含量(ROC)也显著降低。秸秆还田下增加氮肥用量显著提高了水稻抽穗期和灌浆期土壤速效氮含量(AN);推荐施氮处理(165 kg N·hm^-2)的DON和AN含量显著升高;农民习惯施氮处理(195 kg N·hm^-2)降低了DON和AN含量;增加追施氮肥比例对土壤SMBC和DOC含量无明显影响,但提高了水稻拔节期SMBN和ROC含量。【结论】施氮量及其基追比是影响秸秆还田下稻田土壤活性碳氮含量的主要因素,合理配施氮肥能提高土壤微生物量碳、速效氮及水溶性有机氮等活性碳氮组分含量,增加追肥比例也能提高水稻生育期内土壤活性碳氮含量。

【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.