Straw return strategies to improve soil properties and crop productivity in a winter wheat-summer maize cropping system

Crop straw return is widely implemented in winter wheat and summer maize rotation systems. Nevertheless, research characterizing how different straw return methods affect soil properties and grain yield in this double cropping system has been limited. A fixed-site field trial was carried out from 2017 to 2020 to examine the impacts of four straw return methods on the annual changes of soil properties within the top 0–20 cm of soil and grain yield in a winter wheat-summer maize cropping system in North China. The four treatments were: (1) both wheat and maize straw removal (CK), (2) application of only maize straw (W0M1), (3) application of only wheat straw (W1M0), and (4) both wheat and maize straw application (W1M1). The cumulative carbon inputs under the four straw return methods ranged from 11.87 to 36.51 Mg ha−1, which led to changes in SOC stock of −1.30–2.16 Mg ha−1 from 2017 to 2020. Straw return significantly increased the contents of soil organic carbon, mineral nitrogen and available phosphorus. In addition, the soil urease, alkaline phosphatase activities and microbial diversity under straw returning treatment were significantly higher than those in CK. Significant linear relationships existed between annual carbon inputs and soil nutrient contents. And annual straw return had cumulative effects on changes of soil properties. Straw return significantly increased grain yield in the double-cropping system, and significant correlations were observed between the annual changes of grain yield and soil properties. Overall, the W1M1 treatment was the most effective strategy for improving soil properties and crop yield. Return of maize straw alone also maintained relatively high soil fertility with significantly lower carbon inputs, which allows the unused wheat straw to be used for other purposes and maximize the utilization efficiency of all straw resources.