Light reduction in silvopastoral systems and self-shading in treeless grasslands can lead to shade-avoidance responses by tropical grasses. Light environment in association with nitrogen (N) supply influence the growth and nutritive value of forage grasses. This study aimed to quantify forage accumulation (FA) and forage nutritive value of tropical grasses differing in growth habit in environments with contrasting light and N resources. A field study was conducted using ‘Jiggs’ bermudagrass [Cynodon dactylon (L.) Pers.] and ‘Mulato II’ hybrid brachiariagrass (Urochloa spp). Full-sun environments were compared with shaded environments where shade cloth limited incident radiation to 45% of ambient. Low and high N treatments were imposed (30 and 120 kg N ha⁻¹ after each harvest), resulting in a 2 × 2 × 2 factorial arrangement of treatments in four replicates of a randomized complete block design. Forage was harvested every 28 d from May to September in 2014 and 2015 to determine FA. Herbage crude protein (CP) concentration and in vitro digestible organic matter (IVDOM) were assessed. Annual FA was greater for Mulato II than Jiggs and for high-N and full-sun treatments. Species showed similar CP concentrations, but Mulato II had greater IVDOM than Jiggs, likely due to a greater leaf percentage. Shade increased CP concentration of the forages whereas effects on IVDOM were not consistent. Although more productive with greater leaf percentage and nutritive value than decumbent, stoloniferous Jiggs, upright-growing, bunchgrass Mulato II was not persistent when multiple freeze events occurred during winter, limiting its adoption in cooler subtropical environments.

中文翻译：

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遮荫施氮肥影响不同生长习性C4草的牧草积累和营养价值

林牧系统的光照减少和无树草原的自荫可导致热带草的避荫反应。与氮 (N) 供应相关的光环境影响牧草的生长和营养价值。本研究旨在量化不同生长习性热带草在光照和氮资源对比的环境中的草料积累 (FA) 和草料营养价值。使用'Jiggs'狗牙根[ Cynodon dactylon (L.) Pers.]和'Mulato II'杂交腕形草( Urochloa spp)进行了实地研究。将全日照环境与遮光布将入射辐射限制在环境的 45% 的遮光环境进行了比较。实施了低氮和高氮处理（30 和 120 kg N ha ^-1每次收获后），在随机完整区组设计的四个重复中产生 2 × 2 × 2 的因子排列处理。2014 年和 2015 年从 5 月到 9 月每 28 d 收获一次草料以确定 FA。评估了草本粗蛋白 (CP) 浓度和体外可消化有机物 (IVDOM)。Mulato II 的年度 FA 大于 Jiggs 以及高 N 和全日照处理。物种表现出相似的 CP 浓度，但 Mulato II 的 IVDOM 比 Jiggs 更高，可能是由于叶片百分比更高。遮荫增加了草料的 CP 浓度，而对 IVDOM 的影响并不一致。虽然在冬季发生多次冻结事件时，比平伏的、匍匐茎的 Jiggs、直立生长的束草 Mulato II 具有更高的叶片百分比和营养价值更高产，