Fig. 2. Soil NO₃–N content at 0- to 15-cm depth during 1996–1997 and 1998–1999 growing seasons in no-tillage (NT) irrigated maize, for urea fertilization at maize planting (P) and at the six-leaf stage (V6). 0–N is the control; 70 and 210 is kg N ha^-1; F represents flowering; PM is physiological maturity. Asterisks indicates significant effect (P 0.05) of N rate on soil NO₃–N concentration.