As farmers strive to create sustainable cropping systems, the concept of variable rate has become a staple of many cropping plans. The concept of using variable rates started with lime and fertilizer applications-putting the right rate of nutrients where needed instead of over or under applying. The same practice can now be used when planting corn and soybean crops with the use of planters equipped with variable-rate seeding (VRS) technology that allows farmers to change seeding rates as they plant.
Generally, one would think more plants per acre would mean more ears and more yield. This is not always the case as sometimes more ears can mean lighter or less kernels.1 An economic optimum seeding rate must be found. Corn products can tolerate their neighbors much better today than 50 years ago.2 Over the last 50 years, seeding rates and yields have increased. Iowa seeding rates, for example, have increased about 425 plants per acre per year since 2001.2
The economic balance that must be found can be achieved by matching plant populations to productivity “zones” in a field.3 A prescription must be created to spatially match a desired population to a zone. In order to create a zone, field variability must be understood. The “zones” can be built from historical yield data, soil types, aerial imagery, CEC soil maps and other means. Multiple years of yield data from a calibrated combine should be used instead of just one year to find anomalies. The number of zones used in a field may depend on the size of and variability within a field. The creation of three to five zones can usually cover the needs of a field.
Once zones have been built and placed, the agronomic response to each zone must be known to best match the ideal seeding rate to each zone. Channel® Seed customers may utilize the population optimizer tool. Please visit the population optimizer tool at https://www.channel.com/en-us/tools/population-optimizer.html for plant density recommendations for your region. Several other factors should be considered when selecting product seeding rates including plant stalk ratings, nitrogen use, current fertility levels, and economics.
In many instances VRS may lead to lower input costs and higher yields. Often, for corn, seeding rates are increased in higher productivity zones and lowered in lower productivity zones. The opposite is true for soybeans – often, higher planting rates are required in lower productivity zones while lower planting rates can be used in higher productivity zones where more growth and branching can occur.
If VRS is actively utilized, it is important to validate the zones and populations within the zones. Check strips should be included to validate the economic return of the VRS zones. As fertility and agronomics change over time, it may be necessary to change zones and/or prescriptions. The addition of drain tile may greatly impact the yield potential of a region, which can require changes over time.
1Nielsen, R.L. 2013. Thoughts about seeding rates for corn. Corny News Network Articles. Purdue University. https://www.agry.purdue.edu/.
2Abendroth, L. and Elmore, R. 2007. Corn seeding rates and variable-rate seeding. Integrated Crop Management. IC-498. Iowa State University Extension and Outreach. https://crops.extension.iastate.edu/.
3Hawkins, E. and Singh, M. 2019. The art and science of variable rate seeding. Michigan State University Extension. (E. Hawkins is associated with The Ohio State University). https://www.canr.msu.edu/.
Corn yield response to seeding rate. 2019 Research Report. Channel.com. https://www.channel.com/en-us/agronomy/corn-yield-response-to-seeding-rate.html
Web sources verified 3/8/2020
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