Identifying Topographic and Soil Parameters for Variable Seeding Rate Applications in Corn.

The capability to use variable seeding rates has increased dramatically in recent years. Farmers and agronomists frequently collect and analyze soil samples to determine nutrient needs for subsequent crop production. Our objective was to identify the linkage between topography and soil parameters with seeding rates to optimize Iowa corn grain yield. Treatments for this research included five seeding rates (61,750; 74,100; 86,450; 98,800; and 111,150 seeds ha^-1) in a randomized complete block design with five replications at 3 locations in central Iowa. Total cropped area used for the three studies was approximately 35.2 ha. Soil samples were analyzed for soil Olsen-P, Ammonium-Acetate-K, pH, OM, CEC, and texture. Topographic data (elevation, slope, aspect, and curvature) were determined from LIDAR. In four of the six site years, seeding rate was significantly correlated with grain yield, of which, two were moderately correlated and four had low correlation. There was no clear pattern of correlation of variance for soil or topographic parameters across the site-years. A multiple regression with adjusted R-square selection was conducted pooling variables across site-years, resulting in an R-square of 0.06 from inclusion of 7 parameters.  Finally, multiple regressions were conducted for each site-year. The best fit R-square for each site-year regression ranged from 0.12 to 0.63 while the number of variables included in the regressions ranged from 5 to 11.