By Matt Stockton
Agricultural Economist
Background
Cover crops in corn and soybean systems can reduce soil erosion, mitigate nutrient loss, improve soil physical properties, and increase yields. High biomass production is key for cover crops to fulfill these functions, but may not be attainable due to the short window of opportunity for winter cover crops in Nebraska corn and soybean systems. Cover crops may negatively impact subsequent crop yields if they cause soil water deficits or immobilize nitrogen upon their decomposition.
With this study we want to determine the feasibility and impact of winter cover cropping on soil quality, soil water, and crop yields in corn-soybean systems across Nebraska. Our objectives were to quantify cover crop emergence, fall and spring biomass production, soil water changes, soil chemical and physical property changes, and crop yields.
Study Description
Experiments were carried out at four University of Nebraska research sites. The two irrigated studies were at the South Central Agricultural Laboratory near Clay Center and the West Central Research and Extension Center at North Platte. The two rainfed studies were at the Agricultural Research and Development Center near Mead and the Haskell Agricultural Lab near Concord. Five types of cover crops were grown:
- cereal rye (alone),
- forage radish (alone),
- a mix of hairy vetch and winter pea,
- a mix of cereal rye, forage radish, hairy vetch and winter pea, and
- a mix of these four along with red clover, black oats, and forage collards.
Cover crops were planted either early (broadcast into corn or soybeans when corn was at the half-milk stage) or late (drilled after corn or soybean harvest). All cover crops were terminated with glyphosate two weeks before planting corn or soybeans. Variables measured included cover crop emergence, fall and spring biomass production, soil nutrients (nitrogen, phosphorus, potassium and organic C), bulk density, aggregation, water infiltration, soil water, and crop yields.
Applied Questions
Which cover crops produce the most spring biomass? Cereal rye was the highest producer, yielding up to 1,800 lb/ac in the first year and up to 4,800 lb/ac in the second year at the Haskell Agricultural Lab site. Forage radishes winterkilled and the legume mix yielded less than 500 lb/ac at any site-year. Mixes were intermediate in productivity, but most of their dry matter was rye.
Which planting date resulted in the most spring biomass? The early planting date had significantly higher biomass.
What were the impacts on crop yields? Corn yields were 10 bu/ac lower and soybean yields were 4 bu/ac lower after early-planted cover crops at the Haskell Agricultural Lab in 2015. No impacts on corn or soybean yields were found at the other research sites.