Browsing by Author "Wiering, Nicholas"

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    Evaluating winter-hardiness and developing a screening method for freezing tolerance in the leguminous cover crop Hairy Vetch (Vicia villosa R.)
    (2018-01) Wiering, Nicholas
    Hairy vetch (Vicia villosa R.) is a winter-annual legume that is grown as a cover crop and forage. In addition to reducing soil erosion and suppressing weeds, the species can facilitate enough biological N fixation to supplement or replace the N requirements of maize. Although more winter tolerant than most leguminous winter-annuals, it does not reliably overwinter in temperate environments such as the upper Midwestern United States. Our objectives were to screen a collection of accessions for winter-hardiness and develop a screening method for freezing tolerance in a laboratory setting. To identify winter-hardy germplasm, we evaluated the winter survival of 30 accessions in nine Minnesota environments. Mean percent survival among accessions ranged from 15 to 82% and resembled a bimodal distribution. Due to large variation among and within environments, a method of controlled freezing was developed to supplement field evaluations and advance breeding efforts. No differences in freezing tolerance were found among accessions without prior exposure to cold acclimation. However, large differences were apparent when plants were first grown for two weeks in greenhouse conditions and then cold acclimated for four weeks (3°C; short-day photoperiod). Lethal temperatures were determined from six 24-hr programmed freezing treatments. Programmed cycles began at -3°C and gradually decreased to target temperatures ranging from -13 to -21°C. This method of controlled freezing correlated highly with winter survival in field evaluations (rs = 0.77). This study highlights the value of priori testing of experimental parameters in controlled freezing studies and the importance of validating such methods with field evaluations.
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    Methods and knowledge towards the improvement of legume cover crops for the Northern U.S.
    (2021-01) Wiering, Nicholas
    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.).