Effects of controlled-release blended fertilizers on greenhouse gas emissions and nitrate residue in wheat-maize rotation system

Ever-increasing nitrogen fertilizers have posed extreme pressure on the environment for the winter wheat-summer maize rotation system in the North China Plain. Controlled-release fertilizer can be expected to serve as the nutrient-efficient and environment-friendly approach. The available nutrients are applied at controlled rates or concentration levels required for the crop growth in the soil while maintaining the nutrients for a longer period. The controlled-release fertilizers can be considered as an effective measure to improve crop yield and nitrogen use efficiency. This study aims to explore the impacts of one-time fertilization of controlled-release blended fertilizer on the crop yield, greenhouse gas emissions (GHGs) and nitrate residues in the winter wheat-summer maize rotation system. A field experiment was conducted with the summer maize cultivar of Zhengdan 958 and the winter wheat cultivar of Jimai 22. Five treatments were performed on both winter wheat and summer maize, including no nitrogen control (CK), farmers' conventional nitrogen application (FFP), optimized nitrogen application (OPT), CRU1 (the blending ratios of coated urea and traditional urea on winter wheat and summer maize were 5:5 and 3:7, respectively), and CRU2 (the blending ratios of coated urea and traditional urea on winter wheat and summer maize were 7:3 and 5:5, respectively). A comparison was then made on the yield, GHGs, and soil nitrate nitrogen residues among different treatments. The results showed that the nitrogen application significantly improved the single-season and annual crop yield in the wheat-maize rotation system (P<0.05). CRU1 and CRU2 treatments increased the summer maize, winter wheat, and annual yields by 1.4%-3.0%, 1.9%-3.4%, and 1.6%-3.1%, respectively (P>0.05), compared with FFP. Nitrogen application also significantly increased the annual emissions of soil N₂O and CO₂ in the wheat-maize rotation system (P<0.05). The annual accumulation of N2O emissions from soil treated with CRBF1 and CRBF2 was significantly reduced by 27.7%～34.6%, compared with FFP treatment (P<0.05). The nitrogen also increased the annual global warming potential (GWP) of the wheat-maize rotation system (P<0.05). The annual GWP of CRBF1 and CRBF2 treatments decreased by 4.2% and 5.7%, respectively, compared with FFP treatment. There was a significant difference in the CRBF2 treatment (P<0.05). The application of nitrogen reduced the annual greenhouse gas emission intensity (GHGI) of the wheat-maize rotation system. The annual GHGI of CRBF1and CRBF2 treatments decreased by 5.6% to 8.6%, respectively, compared with FFP treatments (P>0.05). CRBF1 and CRBF2 treatments were also reduced by 30.6%-34.3% (P<0.05) for the nitrate nitrogen residues in the 100-200cm soil layer, indicating the lower risk of nitrate nitrogen leaching. In summary, the controlled-release blended fertilizer can be expected to reduce the GHGs and soil nitrate nitrogen residues for the high crop yield. The finding can provide the data and theoretical support for the highly efficient application of nitrogen fertilizer in the winter wheat-summer maize rotation system.