Improving Nitrogen and Water Use Efficiency in Intensive Cropping by Optimized Management and Crop Rotations

Nitrogen (N) and water are key resources for crop production and improving the efficiency with which they are used remains a major global challenge in intensive cropping systems. Here, we report how crop yield, N and water use efficiency, N surplus, and economic benefits can be improved from optimized management and crop rotations. A conventional winter wheat-summer maize double cropping (CN/<i>WM</i>) rotation in a three-year field experiment in the North China Plain is compared with alternative optimized rotations. The first three optimized treatments were wheat-summer maize rotation with optimized N and irrigation rates, tillage and straw management (ON/<i>WM</i>), and partial manure substitution (ONM/<i>WM</i>) or biochar addition (ONB/<i>WM</i>); the fourth optimized treatment was winter wheat-summer maize-spring maize producing three harvests in two years (ON/<i>WMM</i>); and the last was spring maize incorporating green manure during the fallow season for one harvest per year (ON/<i>GM</i>). The results showed that the ON/<i>WM</i>, ONM/<i>WM</i>, and ONB/<i>WM</i> had comparable yields to CN/<i>WM</i>, but significantly increased N use efficiency by 19-41% and water use efficiency by 13-20% and reduced N surplus to 353-531 kg N ha^-1 2yr^-1. From these three optimized treatments, the ONM/<i>WM</i> performed better, with a comprehensive evaluation index of 0.66 and the highest economic benefits. The ON/<i>WMM</i> and ON/<i>GM</i> treatments also significantly increased N and water use efficiency but resulted in relatively low crop yields and profits; nevertheless, they significantly reduced water use and are suitable for water saving cropping systems. We concluded that optimized management-combined manure with synthetic N fertilization in wheat-summer maize rotations can achieve high crop productivity, environmental, and economic benefits, which contribute to a more sustainable crop production.