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 µmol 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.

中文翻译：

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半干旱地区扁桃树对光和养分吸收、作物生长速度和扁桃-谷物农林业系统产量的竞争效应

近年来，农林复合系统管理的重点是减少水土流失和水流失，恢复环境平衡，提高土地利用效率，提高不同地区的经济效益。本研究于 2015 年进行，旨在评估伊朗恰哈马哈尔省和巴赫蒂亚里省萨曼县半干旱地区基于树木的间作系统的种间竞争。从光合有效辐射（PAR）、叶面积指数、作物生长率（CGR）、净同化率（NAR）、残留量等方面对小麦和大麦与杏仁树间作与传统单作进行了比较。土壤中的元素、土壤有机碳和距离树木三个距离（0.5 m、1.5 m 和 2.5 m）的作物产量。根据结果​​，作物截获的PAR随着与树的距离增加而增加。杏仁-大麦和杏仁-小麦系统的最高截获 PAR 分别为 1017 和 796 µmol m -2 s -1 ，距离树木 2.5 m 处。距树干 0.5 m 处的杏树遮荫导致截获的 PAR 减少了约 80%。NAR 和 CGR 重复了这种趋势，它们在距离树 2.5 m 处具有最高值。小麦和大麦的最高谷物产量（分别为 2985 和 2180 kg ha -1 ）是通过距离树木 2.5 m 的间作系统获得的，这比它们各自的单一栽培高 35% 和 39%。土壤中剩余的养分也受到种植系统及其与树木距离的影响。例如，在大麦-杏仁体系中，在远处观察到的土壤有机碳 (0.89 g kg -1 )、总氮 (0.8 g kg -1 )、磷 (15.5 mg kg -1 ) 和钾 (289 mg kg -1 ) 含量最高距杏树 0.5 m，分别比单一栽培高约 55%、63%、48% 和 53%。一般来说，农林复合系统的土壤残留养分量更大。农林业系统中 PAR 的降低是最重要的作物限制，可以通过增加与树木的距离来管理。根据农林复合系统土壤中碳、氮、磷和钾残留的数据，可以得出结论，土壤肥力并未限制作物生长。在距杏树 0.5 m 处观察到土壤中的钾和钾（289 mg kg -1 ），分别比单一栽培高约 55%、63%、48% 和 53%。一般来说，农林复合系统的土壤残留养分量更大。农林业系统中 PAR 的降低是最重要的作物限制，可以通过增加与树木的距离来管理。根据农林复合系统土壤中碳、氮、磷和钾残留的数据，可以得出结论，土壤肥力并未限制作物生长。在距杏树 0.5 m 处观察到土壤中的钾和钾（289 mg kg -1 ），分别比单一栽培高约 55%、63%、48% 和 53%。一般来说，农林复合系统的土壤残留养分量更大。农林业系统中 PAR 的降低是最重要的作物限制，可以通过增加与树木的距离来管理。根据农林复合系统土壤中碳、氮、磷和钾残留的数据，可以得出结论，土壤肥力并未限制作物生长。对于农林复合系统，土壤中残留的养分量更大。农林业系统中 PAR 的降低是最重要的作物限制，可以通过增加与树木的距离来管理。根据农林复合系统土壤中碳、氮、磷和钾残留的数据，可以得出结论，土壤肥力并未限制作物生长。对于农林复合系统，土壤中残留的养分量更大。农林业系统中 PAR 的降低是最重要的作物限制，可以通过增加与树木的距离来管理。根据农林复合系统土壤中碳、氮、磷和钾残留的数据，可以得出结论，土壤肥力并未限制作物生长。