Effects of Different Nitrogen Applications and Field Return Depth on the Diversity and Function of Bacteria in Returned Straw in Cold Paddy Fields

This study investigates the degradation characteristics, bacterial community structure, and degradation mechanism of rice straw under different levels of nitrogen (N) application and depths of return of 1-mature-winter tillage in paddy fields in a cold zone from the perspective of biodegradation by using the nylon mesh bag in situ culture method. Paludibacteraceae and Ruminococcaceae were the dominant bacteria in the degradation process, and their abundance decreased with the increasing depth of return. The activities of extracellular enzymes associated with the C-cycle (α-glucosidase, β-glucosidase, β-cellobiosidase, and β-xylosidase) were generally higher than those of other functional extracellular enzymes, and straw degradation extracellular enzyme activities generally increased in the middle and late stages (104 d). At an N application rate of 110–150 kg hm −2 , the potential functionality of soil showed a quadratic trend with the increasing N application. When the full amount of straw was returned to the field, there was significant spatial heterogeneity in soil potential functionality. Our results showed that the most optimum N application rate was 140 kg hm −2 , while the best soil return level (0–15 cm) was observed in the tillage layer under full rice straw return in the cold zone.