Summer annual grass-legume mixtures may provide supplemental grazing for livestock when cool-season pastures are less productive, but nitrogen fertilizer recommendations for these mixtures are not well established. Inputs to these systems are often high, so optimizing N fertilizer rates may increase appeal to producers. This study evaluated the effects of increasing botanical diversity and N fertilizer application on the yield and botanical composition of summer annual mixtures in four environments in Kentucky. Nitrogen fertilizer rates of 0, 56, 112, 168, and 224 kg N ha^–1 were applied to a sudangrass [Sorghum bicolor (L.) Moench × Sorghum sudanese (P.) Stapf] monoculture, a three-species mixture, and an 11-species mixture. In three out of four environments, sward biomass increased as N application increased (average of 15 kg dry matter (DM) ha^–1 increase per kg N ha^–1; p < .05). Mixture complexity had no effect on forage DM accumulation in three out of four environments (4,000, 5,830, and 7,280 kg DM ha^–1 averaged over mixture for three environments; p > .05). Mixtures were overwhelmingly dominated by grasses, resulting in low functional diversity. Legumes did not respond to N (p > .05), but their contribution to sward DM was <4%. Species compatibility should be a priority when utilizing multi-species mixtures. If a stronger legume component is desired, care must be taken to provide management that favors these species, such as reduced grass-seeding rates to limit competition, especially during initial establishment.

中文翻译：

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氮肥用量对夏季一年生牧草混合物产量和植物成分的影响

当冷季牧场产量较低时，夏季一年生草豆类混合物可为牲畜提供​​补充放牧，但对这些混合物的氮肥建议尚未确定。这些系统的投入通常很高，因此优化氮肥用量可能会增加对生产者的吸引力。本研究评估了在肯塔基州四种环境中增加植物多样性和施氮肥对夏季一年生混合物产量和植物成分的影响。将0、56、112、168和 224 kg N ha ^{–1 的}氮肥施用于苏丹草 [ Sorghum bicolor (L.) Moench × Sorghum sorghum sudanese(P.) Stapf] 单一栽培、三物种混合物和 11 物种混合物。在四分之三的环境中，生物量草地增加如N应用增加（平均15公斤干物质（DM）公顷^-1每千克氮公顷增加^-1 ; p  <0.05）。在四种环境中的三种环境中，混合物的复杂性对草料干物质的积累没有影响（4,000、5,830 和 7,280 kg 干物质公顷^–1三种环境的混合物平均；p  > .05）。混合物以草为主，导致功能多样性低。豆类对 N ( p > .05)，但它们对草地 DM 的贡献 <4%。在使用多物种混合物时，物种兼容性应该是优先事项。如果需要更强的豆科植物成分，必须注意提供有利于这些物种的管理，例如降低草种播种率以限制竞争，尤其是在初始建立期间。