Influence of nitrogen rate on corn grain yield, nitrogen use efficiency, and nitrate leaching on coarse-textured Minnesota soils

Abstract

Nitrogen (N) is often the limiting nutrient in irrigated sandy soils. Nitrogen poses a threat to water quality in its nitrate form because it is easily leached through the root zone of the corn (Zea Mays L.) crop following rain and irrigation events. Leaching is enhanced in sandy soil conditions because sandy soils are particularly well drained. In this study, N was broadcast applied as urea on fields planted with corn at eight rates from 0 kg ha-1 to 314 kg ha-1 in 45 kg ha-1 increments. Urea was applied as a split application with half at planting and half at the V4 growth stage. The study was conducted at four locations, each containing four replications in a randomized complete block. In addition to urea treatments, two coated urea products, Environmentally Smart Nitrogen and SuperUrea, were applied as a single at planting application. Nitrogen uptake, leaf chlorophyll, normalized difference vegetation index (NDVI), grain yield, grain N, nitrogen use efficiency (NUE), basal stalk nitrate (BSN), and residual soil nitrate-N (RSN) were evaluated with respect to N rate. Nitrate-N leaching was monitored with suction tube lysimeters at three of four locations. Results showed an increase in leaf chlorophyll, N uptake, grain yield, grain N, and basal stalk nitrate-N with increased N rate. Normalized difference vegetation index was not affected by N rate for most locations and sampling times. Residual soil nitrate-N and nitrate-N in the leachate tended to be least for the control, but their relationship with applied N rate was not significant because of variability in the data. Nitrate concentration in the leachate was affected by the day of the year at all three locations in which it was evaluated. Coated urea products generally did not increase NDVI, N uptake, NUE, grain yield, or grain N in comparison with split-applied urea at identical N rates. Results for coated urea products were similar to those of untreated urea, despite being applied only at preplant and not as a split application.