Submitted to: Agronomy Journal
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/1/2014
Publication Date: 6/13/2014
Citation: Reese, C., Clay, D., Clay, S., Bich, A.D., Kennedy, A.C., Hansen, S., Moriles, J. 2014. Winter cover crops impact on corn production in semiarid regions. Agronomy Journal. 106:1479–1488. Interpretive Summary: Cover crops are used in agriculture to manage soil fertility, improve soil quality and water use, and reduce weeds, insect pests, and diseases. This study examined the effect of cover crops (winter mustards) in a wheat-corn rotation in semi-arid South Dakota. No-till corn yields were reduced by cover crops due to lack of adequate water and nitrogen. Cover crops contributed to higher bacteria to fungi ratios and reduced soil nitrate-N in the spring. This study showed that in a semi-arid environment, cover crops planted early can reduce yields through increased water and nutrient stress. A cover crop, planted in areas of limited moisture due to either regional climate or landscape, may use valuable soil water in the early spring not leaving enough moisture for the crop. Producers in semi-arid regions are then faced with balancing the benefits of cover crops with the negative aspects of reduced soil moisture for their cash crop. These results are important to producers, agronomists, soil scientists, soil conservation professionals, and extension personnel because the information provides guidance in proper management and use of cover crops to improve yields and soil, air and water quality.
Technical Abstract: Cover crops have been proposed as a technique to increase soil health. This study examined the impact of winter brassica cover crop cocktails grown after wheat (Triticum aestivum) on corn yields; corn yield losses due to water and N stress; soil bacteria to fungi ratios; mycorrhizal markers; and gene regulation in eight key genes. The research was conducted at summit and footslope positions at three northern Great Plains sites in 2011 and 2012. No-till was used at all sites and the fall cover crop seeded after wheat harvest. The following spring the plots were split by 4 N rates (0, 34, 67, and 134 kg NH4NO3-N/ha). Soil was analyzed for microbial biomass, bacteria/fungi ratios, mycorrhizal markers, soil moisture, and inorganic N. Leaf samples, collected at corns V12 growth stage were analyzed for gene response and after physiological maturity grain samples were collected and analyzed for yield loss due to water and N stress using 13C isotopic techniques. At a site with moderate (9.4-13.0 Mg grain/ha) yields, cover crops increased yield losses due to water, which was associated with down regulation in 2 of the 3 marker genes associated with mineral nutrition and one of the two marker genes associated with photosynthesis. At all the sites, the markers for vesicular arbuscular mycorrhizae increased at the summit position, but were not different with cover crop. These results are attributed to the cover crop using water that could have been used by the crop. Findings also showed that winter cover crops contributed to a higher bacterium to fungi ratio and reduced soil nitrate-N in the spring. The study suggests that in a semi-arid environment, cover crops planted early can reduce yields through increased water stress.