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Fig. 1. Method of optimizing N fertilization for winter wheat (left) and summer maize (right) is based on the plant N demands and soil N supply at three growth stages. Soil Nmin was tested in the effective root depth at different growth periods. Nmin target value included N demand by wheat/maize shoot and N demand by root. In the first year (1999–2000), for winter wheat, Nmin target value from regreening to shooting was 120 kg N ha–1, and from shooting to harvest was 125 kg N ha–1. In the years of 2000–2001, 2001–2002, and 2002–2003, the Nmin target value from regreening to shooting was adjusted to 90 kg N ha–1 and the Nmin target value from shooting to harvest was adjusted to 110 kg ha–1.
