Economic Potential for a Pre Sidedress Soil Nitrate Test Based Variable Rate Nitrogen Application in Corn.

An on-farm research study was conducted at seven sites in Southern Minnesota to determine the economic potential of a pre sidedress soil nitrate test (PSNT) based variable rate nitrogen (N) application in corn (Zea mays L.). Treatments consisted of a spring preplant application based on Univ. of Minnesota guidelines (UM) and two split applications, a fixed (FIX) and a variable (VAR) split application. Nitrogen rates varied among treatments and crop rotations but were constant at each research site for the UM and FIX treatments; whereas, the N rate in the VAR treatment varied across the landscape based on PSNT and a productivity zone factor. The split applications were applied preplant and at about the V6 growth stage of corn. Soil samples were taken at V2 and again at V5 (PSNT) to a 60 cm depth in 30 cm increments. The PSNT sample locations for the VAR treatment were determined by soil types and productivity zones, while other treatments were sampled at regular distance intervals. In four of the seven site-years grain yields were affected by treatment. In two of the four responsive site-years corn grain yield was greatest with VAR, and in the remaining two responsive site-years yield was greater with VAR but VAR was not different from FIX. In two site-years FIX and VAR had $65 more combined net profit per acre than UM. In the other five site years UM had a combined $123 more net profit than the average of FIX and VAR. While sidedress can potentially increase yields, the added costs for soil sampling, soil testing and additional fertilizer decreases the potential for economic gain.