By Rebecca Johnson, Agronomy Student at Iowa State University and 2016 University of Nebraska-Lincoln Experiential Fellow
Advisors: Katja Koehler-Cole, Post-Doctoral Research Associate, and Roger Elmore, Extension Cropping Systems Agronomist, both in the Department of Agronomy and Horticulture
While the benefits of cover crops often take years to become evident, the negative effects are typically more immediate and obvious. Cover crops can improve soil structure and reduce erosion. If cover crops are left on the soil surface after termination, the soil remains cool. Cover crops also can immobilize soil N and leave soil water deficits, all of which can slow corn emergence and growth.
Figure 1. Differences in corn development stages on July 21.Figure 2. Corn in the rye-oat (left) and oat plots on June 23.
We carried out an experiment to investigate the effects of grass cover crops on the growth and development of subsequent corn. Cover crops (rye, oats, and a mix of rye and oats) were grown following winter wheat on non-irrigated no-till land at the University of Nebraska South Central Ag Laboratory (SCAL) near Clay Center. The oat cover crop winter-killed and the rye was terminated with glyphosate on April 25 and May 5. Corn was planted into the residue on May 8. Corn density, height, stem diameter, and developmental stage were measured weekly from June 16 to July 21.
Cover crops did not influence corn density. Early in the season, corn stalk diameter and corn height were lower in the rye and rye-oat treatments, but by the final collection date, no differences were found.
To measure corn development, we developed a scale ranging from -2 to +2 (Figure 1) where -2 and -1 represented the last two leaves before initiation of reproductive development, +1 denoted VT, and +2 denoted silk. When this scale was analyzed, we found that the development of corn following oat cover crops was significantly ahead of the development of corn following rye or rye-oat mix. Corn developmental stage in the control plots (no previous cover crop) was intermediate and not different from corn development of any of the cover crops tested.
Several factors probably contributed to this difference in corn development. Heavy residue in the rye and rye-oat mix plots at corn planting could have delayed warming of the soil, slowing emergence and corn development compared to the oat plots, where residue was mostly decomposed (Figure 2).
In addition, soil water availability after rye could have impacted corn growth. Rye was actively growing until two weeks before corn planting, and could have used more soil water than what was replenished by the rains in April and May.
It is also possible that the differences in corn development were due to nitrogen immobilization. The oat cover crop winter-killed and thus had a longer time to decompose than the rye cover crop. Nitrogen in the oat residue might have become available to the corn in May and June, a time when corn N demands are greatest.
From the first year data of this study, it appears that most effects of cover crops on corn growth are short-lived. To understand and alleviate possible negative effects of cover crops, future research should include soil temperature and soil water measurements. Cover crops that winterkill might be more appropriate under non-irrigated conditions in south-central Nebraska, as they allow for soil water replenishment before the next crop is planted. Corn yield data will be collected in the fall and will help determine cover crop impacts on corn yields.
About the Author
Rebecca Johnson
Rebecca Johnson is currently a junior at Iowa State University studying agronomy with a focus in crop management and business. She grew up in rural south-central Iowa and has always had an interest in agriculture.
She has a passion for cover crops and wants to help producers integrate sustainable practices into their current management systems. After graduating, Johnson hopes to attend graduate school to learn more about cover crops and would like to work as an extension agronomist after that. While at UNL this summer, she worked with Roger Elmore, extension cropping systems agronomist, Kenny Roche, post-doctoral research associate, Katja Koehler-Cole, post-doctoral research associate, and Justin McMechan, extension crop protection and cropping systems specialist.
Support for this project was provided by a grant from the USDA NIFA FY15 Agriculture and Food Research Initiative: Education and Literacy Initiative–Undergraduate Experiential Learning Fellowships Program.
