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

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4 Scopus citations


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

Funding Information:
The authors would like to thank Ramer Seeds (Sharon Grove, KY) and Advanta Seeds (Hereford, TX) for supplying the seed for this study, as well as Gene Olson, Gabriel Roberts, Conner Raymond, and Vickie Witcher for assistance in harvesting plots.

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

ASJC Scopus subject areas

  • Agronomy and Crop Science


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