Effects of alfalfa-grain (oil) crop plowing rotation on soil moisture and crop yield in Loess Plateau

In order to evaluate the water adaptability and economic benefit in different rotation systems, and put forward the suitable alfalfa-crop rotation model for the Loess Plateau, the soil moisture and crop yield were investigated,,while the economic benefit of the crop rotation field and fallow land was analyzed after plowing the 6-growth-old alfalfa grassland. The results showed that different alfalfa-crop rotation patterns had differences in restoring the soil moisture. After the post-harvest of the second year, alfalfa-rotation and alfalfa-leisure-leisure modes exhibited the best water eco-environment, soil moisture of which in 0-300 cm layer was close to continuous cropping; the soil moisture recovery layer appeared in 100-340 cm compared with the pre-stage of plowing alfalfa, but alfalfa-winter wheat-winter wheat mode had the worst water eco-environment and its soil moisture recovery layer appeared in 120-320 cm. After plowing the 6-growth-old alfalfa grassland, the soil moisture in 0-500 cm layer of two years for alfalfa-crop rotation was far from the level of continuous cropping. In the first and second year of rotation, the average of winter rape grain yield and water use efficiency respectively were increased by 34.9 %, 44.4 %(P<0.05) than the continuous winter rape cropping. The average of winter wheat grain yield and water use efficiency respectively were increased45.0 %, 42.9 % (P<0.05) than the continuous winter wheat cropping. The benefit analysis in two years showed that the average output to input ratio of winter wheat rotation system was 1.5 times of continuous winter wheat cropping, 2.5 times of winter rape rotation and 3.4 times of continuous winter rape cropping. So the rotation of winter wheat was more suitable and efficient than winter rape after plowing the 6-growth-old alfalfa grassland. The study provide a reference for the sustainable use of alfalfa grassland and establishing a stable agriculture ecological system for dry land.