Water use of interseeded cover crops in rainfed maize–soybean rotations in the Northern U.S.

Introduction Cover crop adoption in U.S. crop rotations is steadily increasing. In the upper Midwest, where the conventional maize ( Zea mays L.)–soybean [ Glycine max (L.) Merr.] rotation is mostly rainfed, there is legitimate concern that cover crops may affect available soil water and the establishment of the subsequent main crop. Methods A study was conducted to evaluate 1) the effect of interseeded cover crops on soil moisture at seeding and termination, and subsequent maize and soybean yields, and 2) seasonal evapotranspiration ( ET ) or water use of the main crops and cover crops. Field trials were conducted from 2016 to 2019 at three locations in the upper Midwest using four treatments: monoculture cereal rye ( Secale cereale L.), two-species rye + crimson clover ( Trifolium incarnatum L.), three-species rye + clover + forage radish ( Raphanus sativus L.), and a fallow (no-cover planted) as the control. Results The ET of cover crops varied between 52 and 110 mm, 70% of which was attributed to its evaporation component. Meanwhile the ET for maize and soybean ranged from 364–516 mm and 378–503 mm, respectively, 20% of which was attributed to evaporation. Regardless of the interseeding strategy, the biomass of cover crops was low in two out of the three experimental years due to weather conditions, resulting in little to no effect on soil water content or crop yield. Discussion Our findings suggest that late interseeded cover crops for conditions in the northern U.S. may have limited impact on soil available water or the productivity of the subsequent crop when cover crop growth is low.