长期秸秆还田与施氮后土壤活性碳、氮的变化

通过长期定位试验,研究了秸秆还田和施氮后小麦生育期内土壤微生物量碳、氮(MBC、MBN)及可溶性有机碳(DOC)的变化,以期为关中麦玉轮作区土壤肥力的提升以及农业的可持续发展提供科学依据。采用裂区设计,主处理为玉米秸秆全量还田(S+N)和秸秆不还田(N),副处理为3个不同施氮水平(0,168,252kg/hm~2)共6个处理。结果表明:土壤MBC从小麦分蘖期至越冬期降低,此后至拔节期升高且达到峰值,拔节期至成熟期降低。各处理土壤DOC从分蘖期至拔节期增加,拔节期达到峰值,此后至成熟期降低;而土壤MBN的动态变化在整个生育期呈现降低的趋势。秸秆还田处理的土壤MBC和DOC显著高于秸秆不还田处理,平均分别提高6.7%和9.3%;秸秆还田后土壤MBN均高于秸秆不还田处理,且在越冬期、拔节期和成熟期达显著水平;各处理的土壤MBC和MBN随着施氮量的增加而显著降低,还田处理的土壤DOC随施氮量的增加而显著增加,平均增加11.8%;而秸秆不还田各处理中土壤DOC含量表现出先增高后降低的趋势。可见,秸秆还田有提高土壤活性有机碳氮的作用,而过量施用氮肥对活性碳氮的提高有抑制作用。因此,关中平原麦玉轮作区实行秸秆还田配合施用适量氮肥是提高土壤肥力水平、实现农业可持续发展的有效措施。

Changes of Active Carbon and Nitrogen in Soil After Long-term Straw Returning and Nitrogen Application

In order to provide a scientific basis for the promotion of soil fertility and the sustainable development of agriculture, a fixed site field experiment was conducted to investigate the changes of soil microbial biomass carbon, nitrogen and dissolved organic carbon after long-term (six years) straw return and urea application in a winter wheat-summer maize rotation system from Guanzhong Plain in Northwest China. The experiment was arranged in a split block design with two main treatments and three subplots, full maize straw return of previous crop (S+N) and no straw return (N) as main plots, and three chemical nitrogen treatments 0, 168 and 252 kg/hm² with four replicates as sub-plots. The results showed that with time soil MBC decreased from tillering stage to wintering stage, then increased until jointing stage and declined later. Soil DOC increased from tillering stage to jointing stage and decreased later with time, the dynamic change of soil MBN in the whole wheat growing season showed a decreased trend. Compared with no straw return treatments, straw return significantly increased the MBC and DOC content in the soil, and increased by 6.7% and 9.3% in average, respectively. MBN in straw return treatments were higher than no straw return treatments, but significantly increased only in wintering stage, jointing stage and maturity stage. With the increase of nitrogen rate, MBC and MBN significantly decreased. While with the increase of nitrogen rate, DOC significantly increased in straw return treatments, and increased by 11.8% in average, but the DOC in no straw return treatments showed an increased trend firstly and declined later. Overall, straw returning could obviously increase soil microbial biomass carbon, nitrogen and dissolved organic carbon, and the application of chemical nitrogen fertilizer promoted the decomposition of maize straw, but excessive application of chemical nitrogen fertilizer decreased the microbial biomass carbon and nitrogen, and will have negative effect on the growth of microorganism. So, straw returning with moderate nitrogen fertilizer is an effective measure to improve the soil fertility and realize the sustainable development of agriculture in the winter wheat-summer maize rotation system from Guanzhong Plain in Northwest China.