Fig. 4. Soil nitrate in the 0- to 30-cm depth during the 2000, 2001, and 2002 growing seasons for shallow (2 cm) and deep (10 cm) N placement in the conventional tillage, no-tillage, and zone tillage corn phase of a wheat–corn–soybean rotation. Error bars are standard error (N = 6). Arrows denote the time of sidedress N application to corn.