Seasonal Temporal Characteristics of In Situ Straw Decomposition in Different Types and Returning Methods

The utilization of crop straw is important for the green development of agriculture and the ecological environment. China’s agricultural planting structure is diversified and straw utilization has received increased attention. Here, in situ experiment with four types of crop straw (i.e., straw of oilseed rape, wheat, rice and corn) was conducted to analyze the effects of climate factors (i.e., accumulated temperature, AT) and straw returning methods on straw decomposition and the release of nutrients. The AT value was an important factor affecting straw decomposition and carbon, nitrogen, and phosphorus release. When straw was incorporated into the soil, the straw decomposition rate could be stimulated when the AT ≥ 600–740 °C. Under straw mulching, the decomposition rate could be further enhanced if the AT exceeded 960–1300 °C. At the end of the experiment, the decomposition and nutrient release rates increased by 39.7–148.7% and 5.8–171.5%, respectively, under straw incorporation compared to straw mulching. The differences under different returning methods in straw decomposition and nutrient release rates were higher in the summer–autumn stage (114.3–148.7% and 14.7–171.5%) than in the winter–spring stage (39.7–47.6% and 5.8–62.5%). The variance in the C/N ratio and the infrared characteristic peak of different straw types affected the decomposition rate and nutrient release characteristics. This study concludes that straw decomposition and nutrient release varied widely among different AT values, straw types, and returning methods.