Kura clover living mulch (KCLM) systems have been investigated for incorporation into upper-Midwestern row-crop rotations to provide living groundcover during vulnerable spring and fall fallow periods. The extended growing season of the cool season legume crop takes advantage of sunlight energy that is not utilized for photosynthesis in monocrop systems; increasing carbon capture, supplies of root exudates to the soil microbiome, and tightening nutrient cycles through active root growth. These conceptual advantages, as well as observed improvements in water infiltration and reductions of soil erosion and nitrate leaching, may help to mitigate regionally important environmental impacts from agricultural production. Designing KCLM systems for upper-Midwestern row-crop production requires consideration of the current production needs and management strategies, and the full quantification of environmental benefits cannot be determined in the absence of robust nitrogen (N) management guidelines for maize production in KCLM systems. The objectives of this study were to (i) determine spring agronomic management strategies that improve N contributions from the KCLM system, and (ii) determine factors influencing N management guidelines for continuous maize grain and stover production in KCLM. These questions were addressed with two field experiments, both conducted at the Rosemount Research and Outreach Center in Rosemount, MN. To determine the effect of agronomic management techniques on in-season N contributions from the KCLM, soil and gaseous N pools were measured over 12 weeks in 2018 following treatment applications of clover residue removal or return and banded herbicide or rotary zone tillage. Clover residue removal did not influence N pool concentrations, while banded herbicide and rotary zone tillage enriched the soil with inorganic N relative to an unmanaged control, where rotary zone tillage was superior to banded herbicide. This experiment concludes that a producer may harvest clover prior to seeding row-crops without altering N management and rotary zone tillage increases in-season N contributions from the living mulch through greater disturbance and incorporation of above and below-ground N-rich clover biomass pools. To determine factors influencing N requirements for continuous maize production in KCLM, a two-year nitrogen rate trial was conducted in 2017 and 2018 on first-year maize and second-year maize after maize following forage management in a KCLM system. This study determined that first-year maize production after at least one year of forage management is self-sufficient in N, while N contributions for second-year maize production is reliant on the number of years in forage management prior to first-year maize seeding. While spring management of the KCLM enriches the soil with inorganic N, this contribution does not provide the total N requirements for high-yielding maize. Continuous maize production in KCLM depletes labile and biomass N pools that accumulate during forage management and subsequent years of crop production require fertilizer N at similar rates to conventional production systems.
University of Minnesota M.S. thesis. June 2019. Major: Land and Atmospheric Science. Advisors: John Baker, Rodney Venterea. 1 computer file (PDF); x, 60 pages + 2 supplementary tables
Nitrogen Dynamics and Management for Maize Production in Kura Clover Living Mulch.
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