Key Parameters for VRT Soybean Seeding Prescriptions.

Growers are collecting many forms of spatial data for their fields including yield, elevation, and soils data. Highly accurate GPS systems along with advances in variable rate technology (VRT) are allowing growers to create and use variable rate planting prescriptions. However, many growers are unsure of which factors to use when making these prescriptions. Finding the key measureable parameters determining soybean seed yield in Wisconsin and using them to create VRT prescriptions are the objectives of this research. In 2013, 11 fields scattered across Wisconsin were each split into zones perpendicular to their predominant soil types and randomly assigned high, medium, or low seeding rates. The seeding rates were confirmed using the as-planted data collected from the planter data logger and multiple plant population counts were taken to document and confirm early season plant densities in each planting rate zone at predetermined georeferenced grid points. The fields were harvested with combines equipped with GPS receivers and calibrated yield monitors. Preliminary analysis suggests no single parameter best explained yield variability across a majority of the fields in 2013. The highest Adjusted-R² value for single explanatory variable regression analysis in any of the 11 fields was 0.39 for soil pH in the Maly field. Individual field analysis will continue for all variables due to the effect location appears to have on the regression results. Trends are also appearing for overall plant population, soil phosphorus, potassium, and organic matter when the data is combined for all fields. 14 different fields are in the study for 2014 and will be analyzed after all data is collected from the growers.