Caroline Lancaster, student at Virginia Polytechnic Institute and State University and 2017 University of Nebraska-Lincoln Integrated Agronomic Systems Intern
Katja Koehler-Cole, Post-Doctoral Research Associate, Department of Agronomy and Horticulture
Roger Elmore, Extension Cropping Systems Specialist

Cover Cropping In Rain-Fed Cropping Systems

Cover crops grown after winter wheat harvest in central Nebraska, can help prevent soil erosion, run-off, and nitrate leaching. Further, they can be used for spring grazing. However, some farmers hesitate to grow cover crops because they use considerable amounts of soil water, tie up nitrogen, and offer habitat for crop pests, all of which may reduce the performance of subsequent corn crops. Furthermore, cost associated with establishing and terminating the cover crop can be prohibitive.

What Did We Measure?

We investigated the effects of grass cover crops on the growth, development, and yield of the following corn crop. Cover crops (rye, oats, and a mix of rye and oats) were planted following winter wheat on non-irrigated no-till plots at the University of Nebraska South Central Ag Laboratory (SCAL) near Clay Center. Oats winter-killed and rye was terminated with glyphosate on April 17. Corn was planted on May 7 into cover crop residue. Corn density, height, stalk diameter, and developmental stage were measured weekly from June 8 through July 19, 2017 and were compared to a control (corn grown without a previous cover crop). This is the second year of data collection in a three-year experiment. (See https://cropwatch.unl.edu/2016/what-are-remnant-effects-rye-and-oat-cover-crops-corn-development.)

Did Cover Crops Influence Corn Growth and Yield?

Cover crops did not influence corn density, corn height or corn developmental stages compared to a control (Figure 1). At the end of June, corn stalk diameter after the rye-oat mix was lower than after the control, but by mid-July, this difference had disappeared. Corn growing after rye showed some damage from wheat stem maggots (Figure 2); however, corn yields after the control were the same as after cover crops, and were on average 209 bu/ac.

How Did Cover Crops Impact Soil Water?

Oats winterkilled and rye was terminated in mid-April when it had about 2,000 lb/ac of biomass (Figure 3). Research from Iowa has shown that rye uses roughly 1 inch of water for every 1,000 lb/ac of aboveground biomass (Martinez-Feria et al., 2016). It’s estimated that the rye in our trials used approximately 2 inches of soil water. Rainfall between the time of rye termination and corn planting totaled 2.79 inches, likely replenishing any soil water deficits left by rye. Further, residue left by oats and rye may have reduced water evaporation from the soil.

What about N Immobilization?

Cover crop residue can tie up soil N when its C:N ratio is greater than 25:1. Rye was killed when it was still in the vegetative stage when it usually has C:N ratios between 15:1 and 25:1. (See https://cropwatch.unl.edu/2016/carbon-and-nitrogen-content-winter-cover-crop-biomass). These relatively low C:N ratios should allow rye residue to decompose rather quickly, releasing N from its tissue back to the soil instead of tying up (immobilizing) soil N.

What about Pests and Cover Crops?

Some corn plants growing after rye showed symptoms of wheat stem maggot damage. The main stem had died and multiple tillers had formed. This problem was observed in other fields in Nebraska, where corn was planted into rye or wheat cover crops that were still alive. (See https://cropwatch.unl.edu/2017/suspected-wheat-stem-maggot-damage-corn-following-cover-crops.)

We followed recommendations to terminate rye cover crops two to three weeks before corn planting to avoid the spread of wheat stem maggots from rye to corn. However, in some spots rye escaped termination, allowing the larvae to infest young corn plants.

Take-Home Message

In rain-fed cropping systems in central Nebraska, cover cropping is possible without negative impacts on the subsequent corn crops if guidelines are observed. First, cover crops should be terminated relatively early and corn should be planted no sooner than two to three weeks later. This gives sufficient time for soil water recharge and residue decomposition. Second, care should be taken to kill rye cover crops completely, otherwise the risk of wheat stem maggots spreading from rye to newly planted corn is high.

About the Lead Author

Caroline Lancaster is one of seven undergraduate students completing an Integrated Agronomic Systems Fellowship at the University of Nebraska-Lincoln in summer 2017.

Lancaster received her BS in Crop and Soil Environmental Sciences: Agronomy Option from Virginia Polytechnic Institute and State University and is now pursuing her MS degree in Crop and Soil Environmental Sciences there.

Support

Support for this project was provided by the USDA NIFA Agriculture and Food Research Initiative: Education and Literacy Initiative–Undergraduate Experiential Learning Fellowship Program and the University of Nebraska-Lincoln Department of Agronomy and Horticulture.