关键词: 秸秆还田, 施氮量, 土壤有机碳, 活性碳组分, 酶活性

Abstract:

【Objective】Straw returning is the main conservation tillage measure in the North China Plain, but long-term shallow rotary tillage has caused problems, such as shallow soil layer and nutrient accumulation, which has become an obstacle to the improvement of cultivated land quality in this area. This study was based on a 2-year field experiment to investigate the effects of different straw returning methods and nitrogen application rates on soil organic carbon components and enzyme activity, for providing a theoretical basis for the rational application of straw in North China.【Method】 The experiment set up different straw returning methods (rotary tillage without straw returning (CK), rotary tillage with straw returning (RT), and deep tillage with straw returning (DT)) and nitrogen fertilizer application rates (180 kg N·hm^-2 (N1), 240 kg N·hm^-2 (N2), and 300 kg N·hm^-2 (N3)) as dual factor treatments to analyze the changes in soil organic carbon and labile fractions and enzyme activity under different straw returning methods and nitrogen fertilizer application rates.【Result】 In 2021-2022 and 2022-2023, compared with CK treatment, straw returning treatment significantly increased the soil organic carbon (SOC) content in the 0-20 and 20-40 cm soil layers, with an increase of 5.6%-20.8% and 10.1%-18.8%, respectively, and increased the content of active organic carbon components, such as soil particulate organic carbon (POC), dissolved organic carbon (DOC), and easily oxidizable organic carbon (ROC). Compared with RT treatment, DT treatment could significantly increase the POC content in the 20-40 cm soil layer and the ROC content in the 0-40 cm soil layer. Under different straw returning methods, the effect of nitrogen application rate on SOC did not reach a significant level, but nitrogen application rate increased the content of some activated carbon components. N2 nitrogen application level was more conducive to increasing POC content in the 0-20 cm soil layer, while N3 nitrogen application level was more conducive to increasing microbial biomass carbon (MBC) and DOC content in the 0-20 cm soil layer. In 2022-2023, compared with the CK treatment, the straw returning treatment significantly increased enzyme activities in the 0-20 and 20-40 cm soil layers by 2.3%-30.3% and 5.1%-50.3%, respectively. Compared with RT treatment, the activity of N-acetylglucosamine glucosidase (N-AG) was significantly increased in the 0-20 cm soil layer treated under DT, but the activities of urease (UG) and β - glucosidase (β-G) were significantly decreased. Under RT treatment, the nitrogen application rate of N2 could significantly increase the activity of UG and N-AG compared to other nitrogen application rates; under DT treatment, the nitrogen application rate of N2 could significantly increase the activity of UG and β - G. In the 0-20 cm soil layer, SOC and DOC were positively correlated with catalase (CG) activity, while ROC was positively correlated with CG and N-AG activity. In the 20-40 cm soil layer, ROC and MBC were positively correlated with most enzyme activities. 【Conclusion】In summary, returning straw to the field could enhance the organic carbon, active components, and enzyme activity of surface and sub surface soils. Deep tillage straw returning combined with 240 kg·hm^-2 nitrogen fertilizer was more conducive to increasing the accumulation of soil particulate organic carbon and easily oxidizable organic carbon, as well as enzyme activity, promoting soil fertility and farmland quality improvement.

Key words: straw returning to the field, nitrogen application rate, soil organic carbon, activated carbon components, enzymatic activity