The Potential of the Pre Sidedress Soil Nitrate Test and Variable Rate Application to Improve Nitrogen Utilization in Corn.

An on-farm research study was conducted at four sites in Southern Minnesota to determine the potential of the pre sidedress soil nitrate test (PSNT) as a tool for improving nitrogen (N) utilization 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. Yields were determined both by combine yield monitor and weigh wagon. Treatments significantly affected corn grain yields at three of the four sites. The VAR treatment had 2, 7 and 18% greater yields than the UM treatment at these three sites; however, the VAR treatment received 59, 68 and 83% more fertilizer N, respectively. Generally, the FIX treatment had equal or slightly less yields than the VAR treatment with considerably less fertilizer N. At all sites Partial Factor Productivity (PFP) was greatest with the UM treatment. Ultimately, the potential of the PSNT for improving N utilization in corn remains unclear. While yields were increased there were added costs for soil sampling, soil testing and additional fertilizer. In addition, the short period of time available for soil sampling, testing and fertilizing was a significant logistical challenge.