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Title: Prohexadione-calcium rate and timing effects on alfalfa interseeded into silage corn

item OSTERHOLZ, WILLIAM - University Of Wisconsin
item RENZ, MARK - University Of Wisconsin
item LAUER, JOSEPH - University Of Wisconsin
item Grabber, John

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/10/2017
Publication Date: 1/4/2018
Publication URL:
Citation: Osterholz, W.R., Renz, M.J., Lauer, J.G., Grabber, J.H. 2018. Prohexadione-calcium rate and timing effects on alfalfa interseeded into silage corn. Agronomy Journal. 110:85-94.

Interpretive Summary: Alfalfa interseeded into corn fields could serve as a dual-purpose crop by providing groundcover during silage corn production and cattle feed during subsequent years of production. In the past, 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. The goal of our research is to identify plant growth regulator (PGR) treatments and management practices that will boost the success rate of alfalfa establishment while limiting yield depression of corn. Our previous work identified prohexadione-calcium as an effective plant growth regulator for doubling the survival of alfalfa interseeded into corn as a dual-purpose cover and forage crop. Subsequent work described in this paper has determined application rates for prohexadione when used in this system. Additional studies are needed to optimize prohexadione application on conventional and hybrid alfalfa varieties that previous research has shown to be better adapted for interseeding into corn. The ultimate aim of this work is to develop reliable and workable corn-interseeded alfalfa production systems that will reduce soil erosion and improve soil health.

Technical Abstract: Prohexadione-Ca (PHD) can enhance establishment of alfalfa (Medicago sativa, L.) interseeded into silage corn (Zea mays, L.), but optimal application rates and timing for this growth regulator are unknown. Two experiments examined how single or split applications of 0.25 to 1.0 kg a.i. ha-1 of PHD on 15- and 25-cm tall glyphosate-resistant alfalfa seedlings influenced growth, stand density, and yield of alfalfa and corn compared to untreated controls. Compared to controls, PHD treatment reduced seedling topgrowth and increased stand density of alfalfa in three out of four locations and in alfalfa dry matter yield in two out of four locations the following year. Alfalfa responses were not consistently influenced by the rate and timing of PHD application, but higher rates proved advantageous under conditions that impaired alfalfa seedling survival under corn. Application of PHD on alfalfa had little or no effect on corn heights and yields. Corn population and alfalfa seeding rates influenced corn silage yield and alfalfa stand counts in at least one location, but these factors had little effect on crop responses to PHD. Combined two-year yields of corn followed by alfalfa were 12% greater for the interseeding system than for solo-seeded corn followed by spring-seeded alfalfa. Overall, a single application of 0.5 to 1.0 kg a.i. ha-1 of PHD on 15- to 25-cm tall alfalfa proved most effective for improving stand density and occasionally yield of glyphosate-resistant alfalfa. Additional studies are needed to optimize PHD application on alfalfa varieties that are better suited for interseeding.