By Alison Robertson, Associate Professor
Despite the environmental and soil benefits that cover crops provide, many farmers are reluctant to try cover crops because of reports of possible yield reduction in the following crop. Recently, Sotorius Archontoulis suggested that biotic factors could influence whether rye affects corn yield.
We hypothesized that a rye cover crop could increase the risk of seedling disease in corn, leading to reduced plant population and yield. The thinking was that cereal rye acts as a “green bridge” that maintains or increases the population of seedling pathogens during the normally fallow period that occurs over winter. Because rye and corn are both grasses, they could be susceptible to some of the same pathogens.
In 2014 and 2015, we did growth chamber and field trials to test our hypothesis. We planted corn at various time intervals after terminating a rye cover crop. The timing of cover crop termination relative to corn planting ranged from 21 days before planting corn to 1 day after planting corn. We collected data on seedling disease, plant growth, and yield. We also recovered seedling pathogens from rye and determined if they could infect corn seedlings.
We found that cereal rye does host seedling pathogens of corn, and these pathogens can proliferate on dying rye plants. In both the growth chamber and field trials, we found when conditions were conducive to disease incidence (i.e., cold and wet) and with shorter time intervals between rye termination and corn planting, it resulted in increased seedling disease, decreased emergence, lowered plant population, reduced plant growth and reduced yield compared to corn planted 10 or more days after terminating the rye and compared to corn planted after a winter fallow period. These effects may not be seen in every year. For example, in 2014 of the field trial, corn yield was reduced only if rye was terminated after planting corn, whereas in 2015 all rye treatments affected corn yield to some extent.
This research suggests that planting corn at least 10-14 days after a rye cover crop has been terminated could reduce the risk of corn seedling diseases following cereal rye, particularly if conditions are conducive for disease. In some years, planting corn at shorter intervals after rye termination may have little effect on disease or yield, whereas in other years disease incidence and yield reductions can occur. Similarly, in some fields the presence or absence of a cover crop may not impact disease incidence at all because pathogen populations are very low or are already very high.
Seedling disease is one of several factors that might affect corn growth and yield following a rye cover crop. Achieving good seed depth and seed furrow closure when planting corn into the rye cover crop residue is also critical to plant population and yield. Additionally, because a large rye cover crop can take up substantial nitrogen (N) during growth, some N fertilizer application at planting, which was not done in these experiments, is usually helpful. Understanding the biological and management factors involved with yield risks following cover crops will enable improved management of cover crop systems, and will bring us closer to realizing the potential of cover crops to improve and protect soil and water quality.
This research was funded through grants from the Iowa Nutrient Research Center and the Leopold Center for Sustainable Agriculture.