Fig. 3. Yield of winter wheat and maize under minimum irrigation (MI) and full irrigation (FI) from 1997 to 2005 (yield difference of winter wheat between MI and FI was significant at P < 0.05 for six seasons, except in 2002–2003 and 2003–2004; for maize, except in 2002 and 2003, yield difference between MI and FI was significant at P < 0.05; bars represent standard deviation).