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Title:   Author  item
                                            Grabber, John
  Submitted to: Agronomy Journal
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 12/21/2015
                                    Publication  Date: 3/4/2016
                                    Publication URL: http://handle.nal.usda.gov/10113/62835Citation: Grabber, J.H. 2016. Prohexadione-calcium improves stand density and yield of alfalfa interseeded into silage corn. Agronomy Journal. 108:726-735.Interpretive Summary: Producers looking to maximize the economic and environmental sustainability of their farms often utilize crop rotations where corn and cover crops are followed by several years of alfalfa production. Unfortunately, farm profitability in this system is constrained by the cost of growing cover crops with corn and by the low yield of alfalfa during its first production year. Alternatively, alfalfa interseeded into corn could provide groundcover during corn production and jumpstart alfalfa forage production the subsequent year, but this system has been unworkable because competition between the co-planted crops often leads to stand failure of alfalfa. Recent field studies have 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. Ongoing work is needed to maximize the reliability and profitability of this production system for a wide variety of farms.
                                Technical Abstract: Interseeded alfalfa (Medicago sativa L.) could serve as a dual-purpose crop to provide groundcover for silage corn (Zea mays L.) and forage during subsequent years of production, but interspecific competition often leads to poor stands of alfalfa and unsatisfactory yields of corn. Four experiments evaluated whether interspecific competition could be alleviated by application of plant growth retardants (PGRs) on alfalfa interseeded at corn planting. In three experiments, foliar application of prohexadione-calcium (PHD) on seedlings approximately doubled stand density of interseeded alfalfa during establishment in corn and following one year of alfalfa forage production. Untimely PHD application in one experiment, however, failed to prevent stand failure of alfalfa growing under warm and damp conditions that favored vigorous growth of corn. When successfully established without PHD, average dry matter yield (DMY) of interseeded alfalfa the year following corn was 85% greater than conventionally spring-seeded alfalfa; prior year PHD application further increased DMY of interseeded alfalfa by 15%. When tested with PHD in two experiments, seed soaking or coating with uniconazole (UCZ) or paclobutrazol (PBZ) reduced stand density and had neutral or adverse impacts on DMY of alfalfa following corn. Interseeding reduced silage corn DMY by an average of 10% compared to monoculture corn and PGR treatment of alfalfa usually failed to alleviate yield depression in corn. Overall, PHD shows promise for enhancing the establishment and subsequent yield of interseeded alfalfa, but further work is needed to refine this production system for farm use.


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