Estimating corn yields
I was on our weekly agronomy conference call Monday morning and Jim Noel, NOAA meteorologist, told us that weather forecasters are calling for a shift in the weather from wetter than average like we had this spring and early summer, to drier than average. That afternoon we got 1.5 inches of rain in Ostrander. It was a little funny at the time, but as I drive around the county and the state there is no doubt that a drier weather pattern did kick in around late June. Noel says that forecasters are predicting that this type of weather pattern will likely continue into August as well. Forecasters are not predicting a drought but are saying that the rainfall will average at or below normal.
This has been a year that really tests a farmer’s ability, and I have to say Delaware County farmers have done a great job. Even with the erratic spring weather pattern. The corn, while uneven in places, looks very good. The warm weather has allowed a growth explosion in many fields. Keep in mind that when corn is at this stage of growth and under favorable growing conditions plants can grow nearly three inches per day. Around the county I have seen a lot of difference in corn size. Some corn is starting to tassel but in the same row, other plants will be much different in size. Farmers need to assess how much of the uneven height is due to uneven emergence. Although some of the variability in plant height can be related to uneven emergence, plant height is not a reliable indicator of plant growth stage in corn. In some fields that show variability in plant height, tall and short plants may actually be at fairly similar stages of growth based on leaf collars.
Peter Thomison, extension specialist at OSU Extension Horticulture and Crop Science, says the question is what impact will variability in development have on crop yields? It’s been well documented that uneven emergence affects crop performance because competition from larger, early emerging plants decreases the yield from smaller, later emerging plants. According to one popular rule of thumb, if two neighboring plants differ by two or more leaves, the younger plant will almost always be barren or produce a worthless type nubbin ear. Several studies have been conducted to determine how later emerging plants impact yield within a field of normal emerging corn.
Research in Ontario indicated that when 17 percent of the plants are delayed in emergence by two leaves, overall yield was reduced 4 percent; when delayed by four leaves, 8 percent yield losses were observed. Plants neighboring late emerging plants only partially offset yield losses. Illinois and Wisconsin research considered the response of corn when 25, 50, or 75 percent of the plants were planted either 10 or 21 days after the original planting date. Overall, grain yields were reduced 6 to 7 percent by a delayed planting of 10 days regardless of the percentage of plants delayed.
However, when planting was delayed 21 days, yields were reduced 10 percent when 25 percent of the plants were delayed, 20 percent when 50 percent were delayed, and 23 percent when 75 percent of the plants were delayed. In a Minnesota study, corn planted normally was compared to that where half of the seeds were planted either 7 or 14 days later. Normal plants had larger stalks, more tillers, longer ears, more ears, fewer barren plants, and more grain per plant than late plants. Yields were reduced more the longer the delay.
Hopefully this will give you some guidance when estimating corn yields this fall. Things look good considering the spring we had but we have a long way to go.
Rob Leeds is an OSU Extension Educator for Agriculture/NR.