By Joel Ransom
In general, plant stands in most corn fields look great this year, especially when traveling on a paved road at the speed limit. However, dry soils, crusting and in a few cases frost damage have cause reduced populations and uneven emergence. I have had a few questions about what that will mean for yields. I previously reported guidelines for replanting based on the percent stand, so in this report I will focus on the impact of lack of uniformity in emergence on yield. Of the main crops planted in North Dakota, corn is one of the most sensitive when it comes to plant population and uniformity in timing of emergence. Partly this can be explained by the small number of seeds that are planted relative to other crops (30,000 for corn verse 1.5 million for wheat) so a missing plant has a proportionally greater impact. Additionally, corn is a poor competitor during early development, so a late emerging plant rarely will achieve its genetic potential and in the worst case will not produce an ear but will compete for light, water and nutrients with neighboring plants. In other words, it becomes an expensive weed. Under the leadership of Lindsay Novak, extension agents and specialists in many regions of the state evaluated corn fields for emergence uniformity in 2013 and 2014. They also quantified the impact of observed planting outcomes on yield within a field and on individual ears. The most common problem observed was plants emerging late (5-7 days after the first flush). In the most variable rows monitored, up to 25% of the corn plants were found to be in this category in 2013. Doubles were rare (<2%), while skips or plants that failed to emerge averaged about 4.4% of the potential stand. Extra-late emergers (10-17 days after the first flush) averaged 4% of the plants.
Data from this study on yield loss based on the category of the plant and its position relative to either a skip or a late emerger are summarized in Table 1. Not surprisingly the most significant loss in yield occurred from skips (seeds that did not germinate, did not get planted or seedlings that failed to emerged). Though plants neighboring these skips grew larger cobs (see photo), this increase could only account for 22% of the yield that was lost by the missing plant. There was significant yield loss from late emergers and as previously mentioned this was the most common category. Moreover, the later the emergence relative to the first flush the greater the yield loss. In this study no late emergers were reported to be barren, though it is not unusual to see plants that emerge late that never produce a cob. They also found that doubles actually increased yields slightly. These data were collected from single ears so there is plenty of chance for errors when extrapolating to a whole field. Nevertheless, hopefully these data will give you some idea of the yield losses you may anticipate if you had issues with stand establishment this season.
