In arid regions, the different intercropping systems reduce interspecific competition to improve system productivity

The aims of this study were (1) to assess which intercropping system is feasible in enhancing soil moisture and promoting crop root growth and (2) to integrate crop root data to assess which intercropping system can reduce interspecific competition and thus increase system productivity. The optimal cropping system was determined by calculating the land equivalent ratio.

In this study, we designed two intercropping systems (intercropped apple–soybean and intercropped apple–alfalfa) and three monocropping systems (monocropped apple, monocropped soybean and monocropped alfalfa) that analysed the effects of these intercropping systems on soil moisture, crop roots, interspecific relationships and yields to determine the most suitable cropping system for local promotion.

Within 50–200 cm from the tree, the apple–soybean intercropping and apple–alfalfa intercropping systems increased soil moisture by 27.91% and 30.23%, respectively, compared to apple monocropping. The root system of intercropped apple was mainly distributed in 20–40 cm soil depth, while the root system of intercropped soybean and intercropped alfalfa moved to shallower soil layers, mainly in 0–20 cm soil depth. In addition, within the distance of 100–200 cm from the tree, soybeans were more competitive than apples and apples were more competitive than alfalfa, whereas apples were more competitive than soybeans and alfalfa at 20–60 cm soil depth. The land equivalent ratio for apple–soybean intercropping system was 1.34 and for the apple–alfalfa intercropping system was 1.18. On balance, apple–soybean intercropping system was more suitable for local promotion.

These results showed that apple–soybean intercropping system has less interspecific competition than apple–alfalfa intercropping system and that the system is more productive and more suitable for local extension.