Nitrate can carry over in many medium and fine textured Wisconsin soils especially when growing season rainfall is below normal and yields are lowered by moisture stress. Most areas of Wisconsin received below normal precipitation during the 2003 growing season, and nitrate carryover could be an important factor affecting nitrogen needs in 2004. Taking carryover nitrate into consideration may be particularly beneficial this year due to the expected higher N fertilizer prices.

Research in Wisconsin indicates that nitrate carryover can be frequent on medium and fine textured soils (Vanotti and Bundy, 1994). Testing soils for residual or carryover nitrate has been examined in the northern Midwest, and procedures for adjusting N rate recommendations for corn have been developed in Minnesota and Wisconsin (Bundy et al., 1992; Schmitt and Randall, 1994; Bundy and Andraski, 1995). Wisconsin recommendations for soil sampling and testing for nitrate carryover are shown in University of Wisconsin extension publications A3512 (Bundy et al., 1995) and A3624 (Bundy and Sturgul, 1994). In brief, the procedure involves sampling soils to a depth of 2 ft in 1-ft depth increments in early spring before corn planting and analyzing these samples for nitrate-N. Nitrate-N in the 2-3 ft depth increment is predicted from the nitrate content of the 1-2 ft depth increment using a model (Ehrhardt and Bundy, 1995). The 0-3 ft nitrate-N content is used to adjust corn nitrogen recommendations for as described in A3624 (Bundy and Sturgul, 1994).