2013 Annual Report
1a.Objectives (from AD-416):
1. Evaluate early- and mid-season growth regulator treatments for promoting the establishment of interseeded glyphosate-tolerant alfalfa without limiting yields of glyphosate tolerant corn.
1b.Approach (from AD-416):
Objective 1: With assistance from the ARS SY, the University of Wisconsin will handle planting of glyphosate-tolerant corn at two locations in May along with fertilizer applications, pest control, and harvesting of whole-plant corn for yield in September at roughly 35% dry matter. The ARS SY will interseed glyphosate-tolerant alfalfa into corn during May and, with assistance from the University of Wisconsin, will handle pest control and measurement of alfalfa forage yields under a 3-cut harvest management during the following year. In initial studies, the University of Wisconsin will spray prohexadione-Ca in June and, with the ARS SY, assess affects on alfalfa growth during corn production and 4–6 weeks following corn harvest. Subsequent studies will examine the use of prohexadione-Ca with other foliar or seed applied growth regulators to identify promising approaches for modulating competition between the co-seeded crops and for enhancing the establishment and subsequent production of interseeded alfalfa. The ARS SY and the University of Wisconsin will jointly plan experiments, analyze data, and publish results.
This research is in support of Objective 2 of the parent project: Improve establishment, harvest management, and storage methods to reduce nitrogen inputs, increase the profitability of crop rotations, increase the recovery of dry matter and nonstructural carbohydrates, improve the energy density of baled hays, and mitigate the negative effects of rainfall on ensiling, storage, and feeding characteristics of rain-damaged silages. In mid-May 2012, corn and interseeded alfalfa were planted at normal versus reduced seeding rates at two sites in Wisconsin. One site was subsequently abandoned because unusually dry spring conditions caused highly variable establishment of interseeded alfalfa. At the second site, the gibberellin-inhibitor prohexadione-calcium was sprayed at several rates via drop nozzles on alfalfa herbage in split applications at 38 and 48 days after planting or in a single application 48 days after planting. The later application was made just before the normal time of canopy closure by corn. We also included non-prohexadione treated control plots seeded only to corn and control plots seeded with corn plus alfalfa. Shifting from a single to a split application of prohexadione proved more effective for reducing alfalfa stem elongation under the corn canopy, but unusually persistent dry conditions throughout the growing season severely stunted corn growth whereas interseeded alfalfa grew vigorously in all treatments. As a result, prohexadione treatment of alfalfa had significant but very small effects on dry matter yields of silage corn in 2012 and on alfalfa dry matter yields and stand density in 2013. Similar experiments of corn with interseeded alfalfa were planted at two sites in 2013 to again compare single vs. split applications of prohexadione. In a separate study, the gibberellin-inhibitors uniconazole and paclobutrazol were used as seed treatments for alfalfa interseeded into corn at both sites in 2013 to assess their value for modulating competition between the co-seeded crops and for enhancing the establishment and subsequent production of interseeded alfalfa. Experiments at one site were largely abandoned in 2013 because unusually wet spring conditions caused highly variable establishment of interseeded alfalfa.