Impact of Cover Crop Strategies on Productivity of Corn

Axel Garcia Y Garcia

The successful integration of cover crops in the conventional corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] rotation in the U.S. upper Midwest is challenging due to poor establishment, use of fall tillage, and a short seeding season. Most research conducted in the region has assessed the benefits of winter hardy cover crops, but research on winterkilled cover crops seeded late in the growing season is very limited. Grower’s interest in cover crops that winterkill lies in practical and economic reasons: to save time and reduce costs associated with herbicide and labor at termination.

The objectives of this study were to 1) assess the establishment and growth of winterkilled cover crops interseeded late into corn and soybean grown within different tillage practices, and 2) determine the effect of those cover crops in the productivity of corn and soybean. The study was conducted in Lamberton and Waseca, Minnesota. Cover crops were hand-broadcast at R5-R6 corn and R7-R8 soybean in fall 2017 and at R3-R4 corn and R5-R6 soybean in fall 2018. Tillage practices were conventional, strip, and no-till; and cover crop strategies included annual ryegrass [AR; Lolium perenne L. ssp. multiflorum (Lam.) Husnot] monoculture, AR = crimson clover (CC; Trifolium incarnatum L.), and AR + CC +forage radish (FR; Raphanus sativus L.).

Results showed that growth of cover crops was marginal. The three-way mixture of ARCCFR produced the highest biomass (151 lb/ac), followed by AR (137 lb/ac) and ARCC at (122 lb/ac) when pooled across years, location, and primary crops. AR monoculture produced more biomass within corn in 2017 in both locations, suggesting that species richness does not always result in higher productivity. In mixtures, AR consistently produced more biomass than CC and FR; CC had the lowest germination and establishment. Cover crop biomass pooled across location, year, tillage, and cover crop strategy yielded 227 lb/ac in corn and 66 lb/ac in soybean. Cover crop canopy cover averaged 24 percent in corn and 8 percent in soybean during the whole study. The yield of primary crops was affected by weather and year, rather than the cover crop strategy and tillage practice.

The practicality of winterkilled/late-interseeded cover crops lies in its potential to produce biomass and provide ground cover. Although these strategies can produce biomass within corn, it is unclear if the amounts can provide ecosystem services. Their marginal performance in soybean suggests that this strategy may not add value within that crop.