Incorporating nitrogen-fixing cover crops into short rotation woody crop (SWRC) plantations may increase soil and tree nitrogen while sustaining, or even improving, yields. This study examined the impacts of Trifolium pratense L. at different seeding rates on soil and poplar N and poplar growth when alley cropped in a one-year old plantation for 2 years compared to natural vegetation and a bare-soil control. These vegetation types were applied in the field under a wide (3.05 m) and narrow (1.82 m) tree alley width. Results showed two of four variations including red clover had 151% and 222% higher soil NO₃⁻ levels compared to controls in the second year (wide spacing/full seed rate and narrow spacing/half seed rate, respectively). This correlated with a 26% and 23% increase, respectively, in poplar leaf N concentrations compared to controls. At the wide spacing and full clover seed rate, poplar foliar P was 80% lower compared to controls, implying significant competition. However, results also showed the potential to mitigate this effect with wider tree spacing and lower cover crop seeding rates, without compromising nitrogen benefits. Although higher foliar nitrogen levels did not correlate with increased poplar productivity within 2 years, the results of this study suggest nitrogen-fixing cover crops can improve soil and poplar nitrogen and may sustain SWRC nitrogen requirements over one or multiple rotations.

中文翻译：

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胡同种植的三叶草的氮素贡献可能维持边缘土地上的短周期木本作物产量

将固氮覆盖作物掺入短轮伐木本（SWRC）人工林中可以增加土壤和树木的氮素，同时维持甚至提高单产。这项研究研究了在同种植被和裸露的土壤中，在一岁的人工林中种植2年的胡同中，不同播种率的三叶叶草对土壤和杨树N和杨树生长的影响。这些植被类型在宽（3.05 m）和窄（1.82 m）的树巷宽度下应用到田间。结果表明：两个四的变化，包括红三叶草具有151％或更高222％的土壤NO ₃ ^-与第二年的对照水平相比（分别为宽行距/全苗率和窄行距/半苗率）。与对照相比，这分别与杨树叶N浓度增加26％和23％有关。在较宽的空间和三叶草的完全播种率下，与对照相比，白杨的叶面磷低80％，这意味着竞争激烈。但是，结果还表明，在不损害氮素效益的情况下，可以通过更宽的树木间距和更低的覆被作物播种率减轻这种影响。尽管较高的叶面氮水平与2年内杨树生产力的提高没有关系，但这项研究的结果表明，固氮覆盖作物可以改善土壤和杨树的氮素，并可以在一轮或多轮耕作后维持SWRC的氮素需求。