Corn and Soybean Grain Yield with Differential Soil Drainage in Minnesota.

The objective of this research was to determine the effects of drainage and N application on corn and soybean grain yields on poorly drained soils. The study was set up in a split-plot arrangement in a randomized complete-block design with four replications, with drainage as whole plot (drained and undrained) and N treatment as split plot. Nitrogen was preplant (PP) applied at 0, 45, 90, 135, 175 and 220 kg N ha^-1 and split application of 45-PP/90-sidedress and 45-PP/130-sidedress for corn. Nitrogen treatments for soybean were check (0-N) and 45 kg N ha^-1 preplant (45-PP), at V4 (45-V4), R1 (45-R1), and R3 (45-R3). Soybean grain yields were similar in drained and undrained soils in 2014, 2015 and 2016 growing seasons. The response to N application in soybean was erratic, grain yields were greater in the fertilized treatments than the check regardless of the time of application in 2015, with no differences in 2016. In 2014, soybean grain yields were greater in the check than fertilized treatment. Corn grain yield was greater in drained (12.3 Mg ha^-1) than undrained soils (10.6 Mg ha^-1) across N treatments in 2015, with no differences in the 2014 and 2016 growing seasons. The three-year mean economic optimum N rate (EONR) calculated from individual years was 129 kg N ha^-1 for drained and 167 kg N ha^-1 for undrained soil. Residual soil N (ammonium plus nitrate in the top 90 cm of soil) at the EONR was 6.4 and 6.9 mg kg^-1 for the drained and undrained soil, respectively. Split-N applications in corn had similar grain yields than preplant application in all three growing seasons.