Nitrogen fertilizer rate effects on yield and botanical components of summer annual forage mixtures

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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.

Original languageEnglish
Pages (from-to)2798-2811
Number of pages14
JournalAgronomy Journal
Issue number3
StatePublished - May 1 2021

Bibliographical note

Publisher Copyright:
© 2021 The Authors. Agronomy Journal © 2021 American Society of Agronomy

ASJC Scopus subject areas

  • Agronomy and Crop Science


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