Establishment and first year yield of interseeded alfalfa as influenced by corn plant density and treatment with prohexadione, fungicide and insecticide

Authors: Grabber, John; SMITH, DAMON - University Of Wisconsin; Osterholz, William - Will; RENZ, MARK - University Of Wisconsin

Submitted to: Agronomy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/3/2021
Publication Date: 11/19/2021
Citation: Grabber, J.H., Smith, D., Osterholz, W.R., Renz, M.J. 2021. Establishment and first year yield of interseeded alfalfa as influenced by corn plant density and treatment with prohexadione, fungicide and insecticide. Agronomy. 11(11). Article 2343. https://doi.org/10.3390/agronomy11112343.
DOI: https://doi.org/10.3390/agronomy11112343

Interpretive Summary: Planting alfalfa in corn silage is one way to reduce soil and nutrient loss from cropland and to improve the productivity and profitability of forage production on dairy farms in the northern USA. One barrier preventing adoption of this technique is unreliable establishment of alfalfa seedlings under corn. The purpose of this study was to determine if alfalfa establishment under corn could be improved by applying several combinations of a plant growth retardant, fungicide, and insecticide to alfalfa seedlings and by adjusting the plant population of corn. Our results revealed that a combined application of all three agrichemicals and planting corn at low to moderate populations provided the best results, but survival of alfalfa seedlings was still less than desired when air temperatures and rainfall were above normal. Therefore additional management practices must be developed to ensure alfalfa can be established in corn under relatively wet and warm growing conditions.

Technical Abstract: Interseeding alfalfa into a corn silage companion crop can increase yields and profitability of forage production and reduce the risk of nutrient and soil loss from cropland, but unreliable establishment of alfalfa hampers adoption of this practice on dairy farms. This study evaluated plant survival, foliar health, and dry matter yields of two alfalfa varieties interseeded into corn when established without agrichemical treatment or when treated with prohexadione (PHD) or PHD followed by fungicide and insecticide (PHD-FI). Penetration of photosynthetically active radiation (PAR) to alfalfa was varied by planting corn at populations ranging from about 47,500 to 100,000 plants per hectare. Plant density of alfalfa following establishment was positively associated with PAR penetration through corn and substantially improved by PHD-FI treatment which limited alfalfa etiolation and defoliation. First-cut dry matter yields of interseeded alfalfa after corn were maximized at a stand density of approximately 200 plants or 850 stems per square meter and total first year yield exceeded conventionally spring-seeded alfalfa by 59 to 75%. Overall our results indicated that PHD-FI treatment and adequate PAR penetration through corn promoted good establishment and subsequent forage production of interseeded alfalfa. Additional management practices must, however, be developed to ensure interseeded alfalfa can be established under corn during relatively wet and warm growing conditions.