Browsing by Author "Alexander, Jonathan"

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    Management Considerations for Maize in Kura Clover Living Mulch
    (2022-05) Alexander, Jonathan
    Kura clover living mulch (KCLM) can be incorporated into upper-Midwestern row-crop production systems to provide perennial living groundcover during vulnerable spring and fall fallow periods. The cool season legume crop takes advantage of an extended growing season to increase carbon capture, provide habitat and nutrition to soil biota, and reduce nutrient loss relative to monocrop maize. These advantages, as well as observed improvements in water infiltration and reductions of soil and nitrate loss, may help to mitigate regionally important environmental impacts from intensive agricultural production systems in the upper Midwest. Designing KCLM systems for upper-Midwestern row-crop production requires consideration of the current production needs and management strategies. The objectives of this research were to (i) determine the effect of row establishment method and fertilizer N rate on maize yield and nitrogen use efficiency, (ii) identify the effect of row establishment method and fertilizer N source on the spatiotemporal distribution of clover and maize roots, and (iii) describe the effect of fertilizer N rate on the spatial and temporal distributions of clover biomass inputs, soil N concentrations, and nitrous oxide emissions within a KCLM for maize. These questions were addressed with two field experiments conducted at the Rosemount Research and Outreach Center in Rosemount, MN and one experiment conducted at Rosemount and the Arlington Research Station in Arlington, WI. The results of this research indicate that optimal row establishment methods during drought conditions depend on the severity of moisture stress, tillage intensity is positively correlated with clover root loss, maize roots were isolated to the tilled row zone to a depth of 0.20 m, and N2O emissions are alarmingly high from the interrow zone under normal growing conditions. The conclusions of this work are that aboveground clover biomass inputs provide a relatively small amount of N to the row crop and that N contributions are sourced from disturbed roots during row establishment. This indicates that N management in a KCLM-maize cropping system is highly dependent on stand history. Finally, 85% of N2O was emitted from the interrow zone in a KCLM under normal weather conditions. This finding indicates that hotspots of microbial denitrification are a potentially significant contributor to N2O emissions in KCLM systems, and that mitigation strategies may depend on clover residue management. Overall, KCLM systems may benefit maize producers in the upper Midwest, but care must be taken to mitigate known management challenges. Further research should be conducted to define remaining management questions and to identify strategies to mitigate high N2O emissions from these systems.
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    Nitrogen Dynamics and Management for Maize Production in Kura Clover Living Mulch
    (2019-06) Alexander, Jonathan
    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.