Improving Nitrogen Use Efficiency in Potato and Sweet Corn On Irrigated Sandy Soils.

Potato and sweet corn are high value, high nitrogen demand crops grown on irrigated sands in Central Wisconsin. As part of the vegetable industry in the region, these crops contribute to $6 billion in economic value to the state. Additionally, groundwater nitrate concentrations in this region in many cases severely exceed drinking water standards. Multiple field trials were conducted between 2009 and 2012 to quantify yield response of potato and sweet corn to alternative N fertilizer practices. Nitrogen use efficiency parameters [e.g. partial nitrogen balance (PNB) and uptake efficiency (UpE)] have been calculated. For potato, use of polymer-coated urea (PCU) applied at less than University recommended rates were the key to improving NUE as there was no loss in yield. However, use of PCU resulted in yield loss on sweet corn. Across years and fertilizer sources, the PNB (N removed with harvest ÷ N applied) for potato ranged from 40 to 92%, although N supplied through irrigation water was not included in these calculations. The UpE [(whole plant N w/ fertilizer – whole plant N w/o fertilizer) ÷ N applied] for potato ranged from 29 to 52%. Sweet corn had a different pattern of PNB and UpE, with relatively low PNB (30-40%), but much greater UpE (69-88%). Three things are clear, (1) use of PCU is a key component of improving NUE in these systems, (2) there are still many gains left to be made in N management on these two crops and (2) these two high N demand crops have very different impacts on N remaining in the soil system at the end of the growing season.