Abstract:

Enhancing interspecific facilitation and reducing interspecific competition are key to achieving ecological and high-quality development in fruit-grass production systems. Fruit trees have stronger competitiveness than grasses， but the impact of fruit trees on the growth of nearby grasses in in orchards and the main limiting factors are still unclear. This study was conducted in Yanchuan， a major jujube （Ziziphus jujube） production area in the Yellow River floodplain of northern Shaanxi. The jujube orchard had a full ground cover of alfalfa （Medicago sativa） and orchardgrass （Dactylis glomerata）， and the biomass of the herbage photosynthetically active radiation， soil nutrients， and water content were measured in different compass directions and at various distances from the jujube trees. Spatial differences were found in the growth of grass in the orchard， with the highest biomass of grass located to the south of the trees （alfalfa 22.57 g·m^-2， orchardgrass 174.57 g·m^-2）， followed by the east and west， and the lowest to the north （alfalfa 14.29 g·m^-2， orchardgrass 71.84 g·m^-2）. Meanwhile， the closer the proximity to the jujube tree， the more the growth of grass was inhibited. In different compass directions from the jujube tree， there were significant differences in photosynthetically active radiation （PAR） intercepted by the alfalfa and the orchardgrass， with the highest PAR to the south and the lowest to the north of the trees. In all directions， the soil nitrogen and phosphorus nutrient content increased with closer proximity to the tree， while the soil moisture content and photosynthetically active radiation decreased， and the root-shoot ratio of alfalfa and orchardgrass tended to increase. These results reveal that the main factor causing the difference in the growth of alfalfa and orchardgrass in different directions from the jujube trees is competition for light. As the distance of alfalfa and orchardgrass from the trees decreased， the main competitive factor between them was water， followed by light. There was no obvious competition in terms of soil nutrients.

Key words: alfalfa, orchardgrass, fruit tree and forage intercropping system, interspecific competition