The competitive effect of almond trees on light and nutrients absorption, crop growth rate, and the yield in almond-cereal agroforestry systems in semi-arid regions

摘要

In recent years, the management of agroforestry systems has been widely focused on reducing the soil erosion and water losses, restoration of environmental balance, increasing the land use efficiency, and elevating economic benefits in different regions. This study was conducted in 2015 to evaluate the interspecific competition in tree-based intercropping systems in a semiarid region of Saman County, Chaharmahal and Bakhtiari Province, Iran. Wheat and barley intercropping with almond trees in comparison with the conventional sole-cropping was investigated in terms of the photosynthetic active radiation (PAR), leaf area index, crop growth rate (CGR), net assimilation rate (NAR), amount of the residual elements in the soil, soil organic carbon, and crop yields at three distances from the trees (0.5 m, 1.5 m, and 2.5 m). According to the results, the PAR intercepted by the crops increased with distances from the tree. The highest intercepted PAR in almond-barley and almond-wheat systems was 1017 and 796 mu mol m(-2) s(-1), respectively, at a distance of 2.5 m from the trees. The shading of the almond tree at 0.5 m from the trunk caused a reduction in the intercepted PAR by about 80%. This trend was repeated for the NAR and CGR, which had the highest values at distance of 2.5 m from the tree. The highest grain yields for wheat and barley (2985 and 2180 kg ha(-1), respectively) were obtained by intercropping systems at the distance of 2.5 m from the trees, which were 35% and 39% higher than their respective monocultures. The remaining nutrients in the soil were also affected by the planting systems and their distance from the tree. For example, in barley-almond system, the highest amounts of soil organic carbon (0.89 g kg(-1)), total nitrogen (0.8 g kg(-1)), phosphorus (15.5 mg kg(-1)), and potassium (289 mg kg(-1)) in soil were observed at a distance of 0.5 m from the almond trees, which were higher than the monoculture by about 55, 63, 48, and 53%, respectively. In general, the amounts of residual nutrients of the soil were greater for the agroforestry system. The reduction of PAR in agroforestry systems was the most important crop limitation, which can be managed by increasing the distance from the trees. According to the data regarding carbon, nitrogen, phosphorus, and potassium residues in the soil of agroforestry system, it could be concluded that soil fertility was not limiting crop performance.