Alfalfa and corn seeded together – John Grabber, USDA ARS
Growing alfalfa in rotation with corn improves yields, reduces the risk of crop loss, reduces fertilizer nitrogen and pest control inputs, spreads cropping and labor activities throughout the growing season, improves soil quality, and reduces cropland vulnerability to nitrate leaching, soil erosion, and nutrient runoff. Alfalfa and corn silage also have complementary nutritional characteristics that benefit livestock when both are included in diets. Thus, growing and feeding alfalfa in conjunction with corn can improve the economic and environmental sustainability of crop and livestock production.
Alfalfa has often been replaced in rotations by corn, in part because corn produces greater forage dry matter (DM) yield than alfalfa. First-year yields of spring-seeded alfalfa are particularly low, often one-half of subsequent full-production years. Planting small grain, grass, or legume companion crops with alfalfa can modestly improve forage yields in the establishment year, but seeding companion crops often reduces forage quality. Thus, new approaches are needed to increase the yield of alfalfa, especially during its first year of production.
One way to bypass the low-yielding establishment year would be to interseed alfalfa into corn to jumpstart full production of alfalfa the following year. During and after establishment, interseeded alfalfa could also serve as a cover crop to reduce soil and nutrient loss from cropland. Unfortunately, this system has been unworkable because traditional intercropping methods require producers to plant corn at low densities (sacrificing high silage yields) to allow reliable alfalfa establishment. Therefore, the USDA-Agricultural Research Service, the University of Wisconsin-Madison, and other institutions have been working to find ways to dependably establish alfalfa in high-yielding silage corn.
Initial studies from 2008 to 2012 demonstrated that foliar applications of a commercially available growth regulator, known as prohexadione (PHD), increased seedling survival of interseeded alfalfa by up to 300 percent during establishment in densely planted corn. Subsequent studies identified suitable rates, timing, and adjuvant mixtures to apply PHD to glyphosate-resistant alfalfa interseeded into corn. Because of its effectiveness and low toxicity, efforts are now moving forward to register PHD for use on alfalfa interseeded into corn.
Work in 2015 and 2016 revealed that several non-GMO hybrid and leafhopper-resistant varieties had two- to 40-fold greater survival than glyphosate-resistant varieties, both with and without PHD treatment. To facilitate the use of non-GMO alfalfa for interseeding, encapsulated acetochlor and bromoxynil were tested and found to have promise as herbicides for controlling weeds. Preliminary work last year suggested applying fungicide and insecticide after PHD can further double the survival of adapted non-GMO alfalfa varieties under corn. Therefore, seeding adapted alfalfa varieties and applying PHD and plant protective chemicals appear to be keys for successfully establishing alfalfa in high-yielding silage corn.
When successfully established, first-year DM yields of interseeded alfalfa were two-fold greater than conventionally spring-seeded alfalfa. In initial studies, alfalfa interseeding reduced silage corn yields by up to 15 percent, but shifting fertilizer nitrogen from the mid- to upper-end of recommended rates largely eliminated yield depression. Rain simulator studies indicated alfalfa interseeding reduced runoff of both soil and nutrients by 40 to 80 percent during and after silage corn production, compared to a conventional system where alfalfa was spring-seeded after corn silage. A preliminary economic analysis of a two-year silage corn and three-year alfalfa rotation suggests alfalfa establishment by interseeding followed by full alfalfa production the following year could improve net return on farms by about 27 percent, compared to alfalfa conventionally spring-seeded after corn silage.
Overall, these improvements in crop yields and profitability, and reductions in soil and nutrient loss, are powerful incentives to continue developing reliable and workable corn-interseeded alfalfa production systems for use on farms in northern states where alfalfa cannot be successfully established in the fall after corn silage harvest.
Forage storage and management