306 Borlaug Hall & Zoom
Kura clover living mulch (KCLM) can be incorporated into upper-Midwestern row-crop production systems to provide perennial living groundcover during 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.
Through careful agronomic design, with consideration to practical and economic constraints, we can remove main barriers to the adoption of this conservation cropping system. Broadly, we aimed to determine the optimal management of KCLM systems with regard to tillage and fertilizer N management through the investigation of agronomic performance and N cycling dynamics. The specific 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.
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 are isolated to the tilled row zone, 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 is 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.