Water use efficiency and sustainability of different long-term crop rotation systems in the Loess Plateau of China

In the dryland region of the Loess Plateau in China, improved soil and water conservation practices are essential for sustainable agriculture. The prevailing cropping practice in this region, growing winter wheat (Triticum aestivum L.) as a monoculture, carries two major drawbacks which arise during the fallow period from July to September: firstly, an exposure to soil erosion from rainstorms and, secondly, poor water storage efficiency of rain. Alternative cropping systems were therefore investigated. They comprised four rotations, each of 3 or 4 years, involving different combinations of corn (Zea mays L.), wheat, broomcorn millet (Panicum miliaceum), and pea (Pisum sativum L.). The water use efficiencies (WUEs) and sustainability of the rotations were evaluated at Changwu Agri-ecological Station in the Loess Plateau from 1984 to 1996. Results showed that two of the rotations gave significantly improved grain yields and WUE compared to the standard wheat monoculture. The rotation of corn, wheat, and wheat–millet could increase the duration of crop coverage during the rainy season from a low of 38% of the time for wheat to a maximum of 80%, and the crop precipitation interception index (CPII) from 53% for wheat to a maximum of 73%. All the alternative rotations tested did not significantly affect available soil water at wheat planting. Considering all factors, a 3-year rotation of corn, wheat, and wheat–millet was found to offer the best potential for improving cropping practice in the region.