Impacts of Cover Crop Diversity and Termination Method On Organic Grain Crop Performance.

Many studies have demonstrated the weed suppressive potential and fertility contributions of individual cover crop species, but the value of diverse cover crop mixtures has received less attention. Moreover, there is increasing interest in conservation tillage strategies for cover crop termination. The objective of this study was to determine the effects of cover crop diversity and termination method on weed suppression, soil nitrogen availability, soil water content, and grain yield in a rotation of organic field crops. A field experiment was conducted between 2009 and 2011 near Mead, NE where spring-sown mixtures of 2, 4, 6, and 8 cover crop species were included in a sunflower – soybean – corn crop rotation. Cover crops were planted in late-March, terminated in late-May using a field disk or sweep plow undercutter and main crops were planted within one week. Cover crop termination with an undercutter decreased weed biomass by 4% (±2.5%) relative to the no cover control at 34 days after planting main crop (DAP) in 2009.  However, the combined effects of increasing cover crop diversity and termination with an undercutter increased weed suppression at 23 DAP in 2010; weed biomass in the undercut 8 species mixture was reduced by 46% (±12.6%) relative to the no cover control. Undercutting cover crops increased soil nitrogen availability (3.2 ppm ± 0.2) relative to incorporation with a disk (2.2 ppm ± 0.2) at 29 DAP in 2010. All cover crop mixtures reduced soil water content prior to main crop planting, while cover crop termination with an undercutter increased soil water content by as much as 7.3% (± 0.2%) compared to the field disk during early main crop growth. Most importantly, cover crop termination with an undercutter increased corn and soybean yields by as much as 32% (±7%) and 34% (±16%) compared to the no cover control, respectively.