Submitted to: Plant Growth Regulator Society of America Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 6/27/2016
Publication Date: N/A
Technical Abstract: Recent USDA-NASS data indicate alfalfa and corn were planted on about 0.8 and 1.9 million hectares per year, respectively, in the Northeast, Great Lakes, Upper Midwest, and Northern Mountain regions the USA. Because both crops are often grown in rotation, alfalfa could be interseeded at corn planting throughout these regions to serve as a dual-purpose crop for providing groundcover during silage corn production and for forage production during subsequent growing seasons. Unfortunately, this system has been unworkable because competition between the co-planted crops often leads to stand failure of interseeded alfalfa. Recent Wisconsin studies demonstrated that properly timed foliar applications of prohexadione-calcium (PHD) doubled plant survival of alfalfa during establishment in densely planted silage corn. The following year, the average dry matter yield of interseeded alfalfa treated with PHD was two-fold greater than conventionally spring-seeded alfalfa. In other work, interseeded alfalfa reduced fall and spring runoff of water and phosphorus by 60% and soil erosion by 80% compared to cropland containing only silage corn residues and weeds. These improvements in crop yields and soil and water conservation are powerful incentives for implementing this production system on farms, but poor seedling survival of interseeded alfalfa at some locations, even with PHD treatment, proved to be a major barrier blocking implementation of this system. Fortunately, a major breakthrough occurred in 2015 when it was discovered that conventional and glyphosate-resistant alfalfa varieties differ substantially in both plant survival and response to PHD when interseeded into corn. In this study, plant density of 20 alfalfa varieties in October, four weeks after corn harvest, ranged from 18 to 90 plants m-2 without PHD and from 55 to 210 plants m-2 with PHD treatment. Plant density responses of varieties to PHD treatment ranged from not significant to an increase of nearly 4-fold. Plant survival of alfalfa was not associated with plant characteristics measured during the growing season or with most plant traits. However, two alfalfa varieties with the leafhopper-resistance trait ranked first in plant survival. Overall, these results suggest the corn-interseeded alfalfa production system could be implemented over a wide array of locations if an appropriate alfalfa variety is sown and treated with PHD.