Prohexadione-Calcium Improves the Establishment and Yield of Alfalfa Interseeded As a Dual Purpose Cover-Forage Crop into Silage Corn.

Interseeded alfalfa could serve as a dual purpose crop for providing groundcover during silage corn production and forage during subsequent years of production, but this system has been unworkable because competition between the co-planted crops often leads to stand failure of interseeded alfalfa and reduced yields of corn. A series of replicated field studies from 2008 to 2014 in Wisconsin identified the gibberellin inhibitor prohexadione-calcium (PHD) as a useful plant growth regulator for enhancing survival of alfalfa planted with imazethapyr- or glyphosate-tolerant corn in early to mid May. Prohexadione sprayed in June with drop nozzles at 0.7 to 1.0 kg per ha typically reduced alfalfa top growth by 20% in July and doubled or tripled alfalfa seedling survival under the corn canopy compared to non-treated controls. First-year yields of alfalfa established the previous year by interseeding were two-fold greater than alfalfa conventionally spring-seeded after corn. Prior year PHD applications increased first year alfalfa yields by 12% and fall stand densities by up to two-fold compared to untreated interseeded controls. Alfalfa interseeding reduced silage corn yields by 9 to 15% compared to corn-only controls and application of PHD on interseeded alfalfa did not alleviate yield depression in corn. Ongoing studies are aimed at identifying the lowest effective rate and optimal timing of PHD application, and further work is needed to lessen yield reductions of corn and to refine production systems for producers. An economic analysis suggests such a system could improve the profitability of first-year alfalfa by $170 to $290 per hectare compared to conventional spring-seeded alfalfa.