Combined Organic Fertilizer and Straw Return Enhanced Summer Maize Productivity and Optimized Soil Nitrate-N distribution in Rainfed Summer Maize-Winter Wheat Rotation on the Southeast Loess Plateau

Organic fertilizer and straw return are sustainable measures for increasing crop yield and improving the soil environment. The present study investigated the effects of combined organic fertilizer and straw return on soil nutrient status, soil nitrate-N distribution, and crop productivity in rainfed maize-wheat rotation on the southeast Loess Plateau. Based on a long-term field fertilization experiment, we reported the effects of four fertilizer management strategies (i.e., chemical NP fertilizers [NP, conventional practice]; chemical NPK fertilizers [NPK]; chemical NP fertilizers combined with organic fertilizer [NPOF]; and chemical NP fertilizers combined with organic fertilizer and straw return [NPOFS]) on productivity in summer maize and winter wheat from 2015 to 2020 season and the soil properties in the 0-60-cm soil layer and the soil nitrate-N distribu-tion in the 0-380-cm soil layer at maturity of winter wheat in 2020. The results averaged from 2015 to 2020 showed that NPOFS increased the grain yield of summer maize by 10.34-11.25%, and water use efficiency by 21.44-32.54%, compared with NP, NPK, and NPOF; however, it had no significant effect on winter wheat yield. All four treatments benefited topsoil (0-20 cm) properties, and NPOFS was superior to NP, NPK, and NPOF in increasing the content of soil organic matter, total nitrogen, available phosphorus, and available potassium, in the 0-60-cm soil layer. Meanwhile, compared with NP and NPK, NPOFS significantly increased soil nitrate-N accumulation by 63.22% and 49.87%, respectively, in the 0-100-cm soil layer and decreased by 24.78% and 10.19%, respectively, in the 200-380-cm soil layer. These results suggest that the combination of organic fertilizer and straw return could improve soil fertility and summer maize productivity and significantly reduce nitrate-N accumulation in the 200-380-cm soil layer. Their use should be recommended for coordinated crop productivity and the soil environment in rainfed summer maize-winter wheat rotation on the southeast Loess Plateau.