Methods and knowledge towards the improvement of legume cover crops for the Northern U.S.

Abstract

Corn and soybean production currently occupy 67% of all Minnesota cropland. Cover cropping, though up more than 40% since 2012, only occupies 2.7% of MN cropland. Logistically, the short growing season in northern states hinders establishment and return on investment for cover crops compared to environments with longer growing seasons. Nonetheless, summer-annual production without winter vegetative cover leaves soil barren for most of the year, making it vulnerable to soil erosion via water or wind. Projections of rainfall intensification in the Upper Midwest may worsen the situation, where ~10 t per hectare of soil are already lost in the Lake States each year. Without vegetative cover from late autumn to early spring, un-sequestered nitrates are easily lost to ground water or waterways, which is accelerated by the 37% of MN cropland above tile drainage. Cover crops provide one method to reduce these negative externalities of crop production on MN landscapes. However, the immediate challenge is incorporating them into an already established cropping system, without reducing the productivity or profitability of that system. Legume cover crops, if able to survive harsh winters, could provide an economic incentive to farmers due to biological N fixation, which could also reduce global reliance on synthetic-N, which is the most energy-expensive input for convention farmers. However, very little effort has been made to improve legume cover crops for Northern U.S. cropping systems. To improve the performance and adaptability of legume cover crops, foundational research will be required that provides knowledge of traits of interest (Chapter 2), methods to select desirable phenotypes (Chapter 3), and resources to facilitate variety improvement (Chapter 4). Though the challenges of cover crop improvement and implementation are much the same for legume species, this thesis primarily focuses on improvement efforts for the winter-hardy annual legume, hairy vetch (Vicia villosa R.).