Establishment and First Year Yield of Interseeded Alfalfa as Influenced by Corn Plant Density and Treatment with Prohexadione, Fungicide and Insecticide

Abstract

Interseeding alfalfa (Medicago sativa L.) into a silage corn (Zea mays L.) companion crop can increase the yield and profitability of forage production and reduce the risk of nutrient and soil loss from cropland, but unreliable establishment of alfalfa hampers the adoption of this practice on dairy farms. This study evaluated plant survival, foliar health, and dry matter yields of two alfalfa varieties when established in corn sown at populations ranging from about 47,500 to 100,000 plants per ha−1 and when treated with prohexadione (PHD), PHD followed by fungicide and insecticide (PHD-FI), or not treated with agrichemicals. The plant density of alfalfa during establishment was adversely impacted by above average precipitation and high corn populations, but substantially improved by PHD-FI treatment, which limited alfalfa etiolation, disease, and defoliation. First-cut dry-matter yields of interseeded alfalfa after corn were maximized at a stand density of approximately 200 plants m−2 or 850 stems m−2 and total first year yield exceeded conventionally spring-seeded alfalfa by 59 to 75%. Overall, our results indicated that PHD-FI treatment promoted good establishment and subsequent forage production of interseeded alfalfa. Applications of PHD-FI must, however, be fine-tuned, and additional management practices must be developed to ensure both good yields of corn silage and reliable establishment of interseeded alfalfa, especially during wet growing conditions.

Ecological Intensification of Food Production by Integrating Forages

“…Successful establishment of forage legumes in a maize-silage companion crop for subsequent forage production appears to be highly dependent on management practices, growth environment, and the developmental characteristics and yield potential of maize. Multi-year studies in Wisconsin, USA demonstrated that alfalfa establishment in maize silage is favored by early interseeding prior to the V2 stage of maize using normal alfalfa seeding rates, and by planting maize at moderate maize populations to lessen competition and allow some penetration of direct sunlight to alfalfa seedlings following maize canopy closure [132][133][134][135]. Establishment of interseeded alfalfa in Wisconsin was further enhanced by planting a suitable variety [136] and by treating seedlings with the gibberellin inhibitor prohexadione followed by fungicide and insecticide to promote root growth and overall plant health [132][133][134]136].…”

“…Several options for controlling weeds have also been developed for interseeding systems utilizing glyphosate-resistant and non-GMO alfalfa and maize [139]. Alfalfa variety selection and agrichemical use is of little consequence, however, if establishment is carried out under conditions that favor an open maize canopy, relatively low yields of maize, and low pressure from weeds, disease, or insects [133,135,136,139]. Red clover (Trifolium pratense L.) has typically been interseeded into maize at the V4 to V6 stage as a short-term cover crop, and although establishment can be inconsistent, it can in some years produce high yields of forage the following year [140].…”

Establishment of alfalfa interseeded into corn in response to one cycle of selection and hybridization

“…Final stand density in late October was not related to stand density in early July (covariate p = 0.77). A prior study also found that comparable variations in plant density among alfalfa varieties early in the growing season had no effect on final stand density following corn harvest (Grabber et al., 2021).…”

“…Final stand densities of several polycross entries averaged 115 plants m −2 and one hybrid entry averaged 147 plants m −2 when established with PFI. A recent study found, however, that stand densities of interseeded alfalfa approaching 200 plants m −2 following corn harvest would be needed to maximize alfalfa yield the following year (Grabber et al., 2021). This indicates several cycles of selection for this trait will be needed to ensure stands of interseeded alfalfa following corn harvest will be sufficient to maximize subsequent forage production.…”

“…Improved intercropping practices, such as early interseeding of alfalfa, proper weed control and crop seeding rates, and foliar application of prohexadione, fungicide, and insecticide (PFI) have improved the reliability of alfalfa establishment under corn (Grabber, 2016; Grabber et al., 2021; Osterholz et al., 2021; Osterholz et al., 2018; Osterholz et al., 2018). Unfortunately, establishment during wet growing conditions exacerbates alfalfa seedling death due to high disease pressure and excessive competition from corn, leaving swards with inadequate plant density to support high yields of forage in subsequent years (Grabber et al., 2021). Therefore, further work is needed to identify means for ensuring reliable establishment of alfalfa under wet growing conditions.…”