Prohexadione‐Calcium Rate and Timing Effects on Alfalfa Interseeded into Silage Corn

Abstract

Core Ideas Higher prohexadione rates of 0.5 to 1 kg a.i. ha–1 enhanced interseeded alfalfa establishment and yield under stressful establishment conditions.Prohexadione application to 15 vs. 25 cm tall alfalfa seedlings provided similar improvements in alfalfa stand density and yield.Interseeding alfalfa increased overall corn+alfalfa forage production by 12%. Prohexadione‐calcium (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 applied to 15 or 25 cm tall glyphosate‐resistant alfalfa seedlings influenced growth, stand density, and yield of alfalfa and corn compared to untreated controls. The PHD treatments reduced seedling top growth by 13 to 32% and increased stand density of alfalfa by 19 to 81% in three out of four locations and alfalfa dry matter yield by 4 to 23% 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 2‐yr 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 effective for improving stand density and occasionally first year yield of glyphosate‐resistant alfalfa.

Alfalfa establishment with sorghum–sudangrass as a companion crop

“…Interseeding alfalfa within a few days of corn planting provides soil and water conservation benefits including increased living plant cover and reduced soil and nutrient runoff losses during and after corn silage production (Osterholz, Renz, Jokela, & Grabber, 2019). Although the technology shows promise, it is not quite ready for adoption (Osterholz et al., 2018), and traditionally, producers might pair alfalfa with fast emerging companion crops to increase seeding‐year forage production (Buxton & Wedin, 1970; Hoy, Moore, George, & Brummer, 2002; Simmons, Sheaffer, Rasmusson, Stuthman, & Nickel, 1995; Wiersma, Hoffman, & Mlynarek, 1999) and suppress weed growth (Hall, Curran, Werner, & Marshall, 1995; Rehm, Sheaffer, Martin, & Becker, 1998). The use of companion crops provides an alternative to chemical applications for weed suppression (Hunt, MacAdam, & Griggs, 2016; Simmons et al., 1992) and, through an increase in ground cover, they help protect soils from wind and water erosion (Simmons et al., 1992, 1995; Wiersma et al., 1999).…”

Intercropping and relay cropping to increase productivity, resilience, and long-term sustainability of corn and soybean cropping systems in Iowa

“…Similar to 2016, application of PHD did not affect the aboveground biomass or grain yield between the intercropped treatments in 2017. Similar findings were reported in the studies conducted by Osterholz et al (2018) in Wisconsin, where application of PHD on alfalfa had little or no effect on corn plant height and grain yield when alfalfa was intercropped with silage corn. Reductions in corn biomass and grain yield in 2017 were likely the result of a drier summer and inadequate available soil moisture.…”

“…Similarly, corn grain yield was reduced by 24.5% when intercropped with alfalfa (with or without PHD application). Reduction in silage yield when corn was intercropped with alfalfa was reported by Osterholz et al (2018). Similar to 2016, application of PHD did not affect the aboveground biomass or grain yield between the intercropped treatments in 2017.…”

“…It reduces internode elongation (Rademacher, 2000), resulting in increased alfalfa leaf/stem ratio and improved survival under the silage corn canopy (Grabber, 2016). Intercropped alfalfa treated with prohexadione in the seeding year competed less with the corn and improved the survival the survival rate of alfalfa intercropped with silage corn (Osterholz et al, 2018). First-year yields of alfalfa established as an intercrop with corn the previous year were two-fold greater than alfalfa spring-seeded after corn.…”

“…In a corn-alfalfa intercropping system corn would serve as a companion crop to alfalfa during establishment and alfalfa would serve as a cover crop after corn harvest, while also having potential to enhance productivity by bringing alfalfa into full forage production the following year. With the availability of glyphosate-tolerant corn and alfalfa, and the use of growth regulators (Osterholz et al, 2018), corn-alfalfa intercropping has potential in Iowa.…”