High corn seeding rates don’t necessarily mean higher profits
Technology and equipment --- yield maps, global positioning systems (GPS), variable rate planters, etc. --- allows farmers to assign seeding rates to zones within fields.
“Yield maps, aerial imagery and other precision agriculture layers are great at showing the level of variability within fields so it may make sense to vary the (planting) rate,” Reeg said. “However, predicting where to vary planting rates and by how much has proved challenging.”
By testing two populations within the range farmers would consider planting, farmers can find out where low rates do better than high and vice versa.
click image to zoomFigure 1. Aerial imagery with soil map units (SMU’s). Notice the amount of variability within SMU’s. “If you’re going to build zones, shouldn’t you know where you get a better return on investment?” Reeg concluded. “I often see zones created from soil map units that do not align well with the actual soil transitions in the field as shown below in figure 1.
A corn planting rate trial last year in Black Hawk County is a good example, Reeg said. Strips of 28,000 and 34,000 seeds per acre were planted across the field. After emergence, nine areas were checked for uniform stand.
The yield varied by 115 bushels per acre between good soils with high water holding capacity compared to sandy areas. The higher planting rate outperformed the lower rate by 1.2 bushels per acre across the field. But after the cost of the extra seed was factored in and corn at $5 per bushel, the high population lost about $16.50 per acre compared to the lower rate.
Figure 2. Yield map showing variability within a Black Hawk county field. The areas colored green out yielded the red areas by over 115 bushels per acre. The farmer found out the low population out yielded and financially outperformed the higher population in the less productive area (12.6 acres) by about $15 per acre, while the high population in the high productive area (41.4 acres) lost about $1 per acre. “There’s no doubt changing population can impact yields,” Reeg said. “Whether it’s financially good is another thing. Validating the yield difference of planting rates is an essential step in developing variable rate planting prescriptions.”
Reeg encourages farmers looking to improve profitability to test products and management practices on their farms using replicated strip trials.