Soil moisture preservation and improving of crop yield in dry land under long-term wheat/maize rotation

Abstract: Conservation tillage including no tillage and subsoiling with straw mulching can reduce soil disturbance and superfluous evaporation, reserve more soil water and enhance soil fertility, and promote the crop yield. However, applying mono tillage practices in a long term would decrease the crop yield, and bring some defects for the environment and limit the growth of crop. Tillage rotation rotated different soil tillage practices in a rational sequence, and it combined the conventional tillage, rotary tillage, no tillage, and so on. An optimal rotation can alleviate some disadvantages brought by long-term mono tillage. Now the research on tillage rotations mainly focused on rotation of no tillage with subsoiling and short term (2-5 years) tillage experiment. However, the effect of conservation tillage rotation is a long and slow process. And the research on some other tillage rotations was less. To explore the optimal tillage rotation for the winter wheat-spring maize system on Loess Plateau, a long term experiment was conducted in Heyang County, Shaanxi Province from 2007 to 2017. There were 4 tillage rotations in this experiment: rotation of no tillage with subsoiling (NS), rotation of subsoiling with conventional tillage (SC), rotation of conventional tillage with no tillage (CN), and continuous conventional tillage (CT). The effects of tillage rotations on soil water use and soil water conservation and crop yield increase were detected in 10 years, and there were 5 whole tillage cycles during this experiment. The result showed CN rotation enhanced soil physical property in 10 years, and the soil bulk density of CN rotation was 1.31 g/cm3 in the soil depth of 0-60 cm. Tillage rotations can reserve more soil water in fallow period, CN rotation was the best one, and the mean soil water storage was 385.8 mm in 10 years. During crop growth season, tillage rotations can provide better soil water condition for crop growth, and CN rotation had better soil water condition during crop growth season in winter wheat - spring maize rotation. Moreover, tillage rotations can increase the crop yield and water use efficiency (WUE) when compared with CT treatment. In 10 years, CN produced higher yield and WUE of winter wheat and spring maize; the average values of crop yield were 5221 and 7433 kg/hm2, respectively, and the average values of WUE were 15.5 and 20.7 kg/( hm2·mm), respectively. In 2007－2017, CN rotation provided the best economic profit, and the average value was 6254 yuan/ hm2. In 2007, water deficit in key growth season of spring maize limited the crop yield, yield of NS, SC and CT treatments declined significantly, and the economic profits were all in negative values, but CN rotation produced higher crop yield and better economic profit than other tillage treatments. This illustrated that CN rotation was more suitable for the crop production in arid area and dry year. In a comprehensive consideration, the CN rotation enhances the soil property effectively, reserves more soil water and produces higher crop yield, and is the optimal tillage system for the sustainable development of dryland agriculture.