Building a Nitrogen Recommendation for Irrigated Sweet Corn.

Wisconsin ranks second nationally in the production of sweet corn grown for processing. The sweet corn is grown primarily in the Central Sands Region of Wisconsin and under pivot irrigation. Most fields exceed the recommended rate of nitrogen (N) for this crop because of the high loss environment (sandy soil) and the high value of the crop. Over application of nitrogen common and used primarily as a form of insurace. However, this, in part, has led to an increase in groundwater nitrate concentrations that far exceed the drinking water standard. To evaluate the effect of N magement on sweet corn yield and economics, we conducted to seperate experiments: 1) on-farm N rate trials and 2) N rate, variety, and seeding density experiments. The objective of this research was to: 1) determiene the agronomic and economic optimum N rate for this production system and 2) determine which management practices can be applied to reduce the need for additional N or improve nitrogen use efficiency. Results from these studies indicate that the currently recommended rate of 168 kg ha^-1 is adquate for optimum yields, although the small, non-staticially significant yield increases with additional fertilizer can result in an increase in net economic return. Newer varieties of sweet corn out-yield older varieites, but the optimum N rate is similiar. There was not a significant increase in cut kernel yield above 168 kg ha^-1, so this rate can be considered the optimum rate for both fresh market (ears) and processing (kernel) yields.