Corn field edge effect has once again show up in Iowa. It is raising questions about what is causing it. In 2019 and 2020, I was able to conduct some exploratory data collection to learn more about the phenomenon.
What is it? Edge effect in corn is where the outside rows of corn fields have depressed yields compared to the field interior. This has been most pronounced when the adjacent field is a soybean, hay, or pasture and typically on the southern or western sides of the field. Our experience is that it is much more evident in drought years.
What is causing it? It is often thought to be caused by herbicide drift and this is a plausible cause. However, in our experience we could not confirm herbicide drift. Our work suggests the phenomenon is caused by a combination of corn microclimate and weather patterns. Air passing over and mixing into the corn canopy is initially dryer at the field edge and, due to plant respiration, the air collects more moisture as it passes further into the field. Thus, corn respiration rates are higher (e.g., think more water use occurring) along the field edges because of the drier air. Over time, the greater water use leads to elevated drought stress along the field edges.
What is the yield penalty? In our work with 7 locations in Iowa, the yield penalty was 35 to 70 bushels/acre (figure 1). However, in 2019 the number of kernel rows and kernels per ear were not affected but at 2 of 4 sites the kernel weight was smaller along the edge of the field. In 2020, at 1 of 3 sites, both kernels per ear and kernel weight were reduced. This suggests the timing of stress is occurring in July and August during pollination and grain fill and not during ear formation (V6 to ~V14).
Figure1. Corn edge effect influence on corn yields from the edge of the field at 7 locations in 2019 and 2020.