Effects of Different Green Manure Crops on Soil Water, Nitrogen, and Yield: Preliminary Results in an Apple Orchard on the Loess Plateau, China

Abstract

Green manure crops intercropping is an effective agricultural practice to alleviate water and nutrient deficit by improving soil properties in the Loess Plateau of China. However, green manure crops intercropping could cause water and nutrient competition, but the effects of different green manure crops intercropping on soil water and nutrient status are rarely evaluated. Thus, we conducted a field experiment to investigate the responses of soil moisture, nitrogen, and yield to green manure crops intercropping. Three intercropping patterns, apple–ryegrass (AR), apple–spring rape (AS), and apple–alfalfa (AA), were set up with a blank control (CK), which employed clean tillage in the inter-row and row. All treatments had no significant difference on evapotranspiration. At maturity, AR, AS, and AA treatments reduced soil organic matter content by 4.2%, 6.5%, and 18.8%, and total nitrogen content by 0.01%, 1.3%, and 20.3%, relative to CK, respectively. The water competition degree in AR, AS, and AA were 38.4%, 48.8%, and 64.6%, respectively. Ryegrass, spring rape, and alfalfa’s nitrogen use efficiency were 19.71%, 29.24%, and 39.42%, respectively. AR and AS treatments increased the apple yield by 11.7% and 5.7%, and water-use efficiency (WUE) by 14.4% and 7.5%, relative to CK, respectively. AA treatment reduced the apple yield by 6.9% and WUE by 6.8%, relative to CK. All treatments had no significant difference on apple quality. Therefore, in normal water years, we suggest adapting the ryegrass–apple tree intercropping pattern for apple production on the Plateau Loess, China.