Can Corn Benefit From Social Distancing?

Dr. Alison Robertson and Sarah Kurtz

Occasionally, corn planted after a cereal rye cover crop may have reduced yields. Proposed reasons for this yield decline include allelopathy, seedling disease, nitrogen immobilization and poor planter performance. In our lab, we are interested in understanding how seedling disease and allelopathy contribute to corn yield decline to develop best management practices for growing corn after a cereal rye cover crop. We will save the allelopathy story for another blog, and focus on seedling disease in this blog.

Corn seedling disease pathogens survive in the roots of cereal rye. We wondered if planting corn at a distance from a cereal rye crop, in other words “social distancing” the two crops, might reduce seedling disease and mitigate yield loss.

In 2019 and 2020, with funding from the Iowa Nutrient Research Center, we investigated the effect of “social distancing” on corn planted after a winter cereal rye cover crop. To do this we planted cereal rye in three spatial arrangements (treatments) and compared corn growth and development, seedling disease and yield of corn among the three treatments and a no cover crop control. We (i) broadcasted cereal rye, (ii) drilled cereal rye in three 7.5” rows in the corn interrow and (iii) drilled one row of cereal rye in the corn interrow. Thus, when corn was no-till planted, the corn was 0”, 7.5” and 15” away from the cereal rye residue (Figure 1).

Figure. 1. Diagram showing treatments to assess the effect of social distancing on growth, seedling disease and yield of corn.

Table 1 summarizes our results. In 2019, corn seedlings were shortest when corn was planted 0” from cereal rye residue and tallest when the corn was planted 15” from the cereal rye residue. Corn shoot height did not differ among the treatments in 2020. Corn seedlings were most vigorous (approximately half a growth stage ahead and heavier) in the no cover crop control and when corn was planted 15” from the cereal rye residue compared to the corn planted within the cereal rye residue. In general, seedling disease was low and did not differ among treatments in 2019. In 2020, however, disease was more severe in seedlings planted within the cereal rye residue and 7.5” from the cereal rye residue than seedlings planted following no cover crop or planted 15” from cereal rye residue. In 2020, more barren plants were observed in corn planted into cereal rye residue compared to the other treatments.  In both years, corn yield generally decreased as corn was planted closer to cereal rye residue.

Table 1. Growth parameters and radicle rot severity at V2 to V3, barren years, and yield of corn planted at various distances from cereal rye cover crop residue in 2019 and 2020.

These data suggest that physically distancing the corn crop from the cereal rye cover crop is one way to reduce the negative effects of a winter rye cover crop on corn. As precision planting becomes more common on Iowa farms, it is possible farmers could deliberately seed a winter cereal rye cover crop in the interrows to physically separate the cereal rye from the corn rows planted the following season. Note however, in this study we did not investigate the effects of social distancing corn from cereal rye residue on the ecological services that a rye cover crop provides. A primary reason for growing cover crops is to protect soil and improve water quality. Other reasons include weed management and improving soil health. Since less ground is covered when a single row of cereal rye is seeded in 30-inch rows, there is more bare ground that may be subject to erosion, reduced infiltration and weed establishment. Moreover, the cereal cover crop may capture less nitrate, resulting in more leaching and reduced improvement in water quality. Further studies to understand the effects of winter cereal rye spacing arrangements on erosion, water quality, and weed control are needed.