| By using the optimum regression design of three factors and four levels, the experiment of balanced fertilization was carried out on the dry land in Xiji county of south Ningxia for the main crops during 20012003. The results showed that, in the semi-arid areas with 350400 mm precipitation, the optimum fertilization combination for wheat was N 120 kg/hm2, P2>O5 90 kg/hm2, K2O 30 kg/hm2; for pea was N45 kg/hm2, P2>O5 180 kg/hm2, K2O 40 kg/hm2; for film-mulched corn was N270 kg/hm2, P2>O5 120 kg/hm2, K2O 60 kg/hm2; for potato was N225 kg/hm2, P2>O5 72 kg/hm2, K2O 80 kg/hm2. |