Relationship Between Water and Fertilizer for Wheat and Effect on Wheat Yield in Rainfed Field of Loess Plateau

Relationship between water and fertilizer was investigated for three years in isolated microplot experiments. An approximately linear relationship was found between the water content and the wheat yield when the amount of fertilizer was constant. However, the relationship between the amount of fertilizer and the wheat yield was parabolic when the amount of water supply was constant. The amount of nitrogen and water content had a positively alternative effect but the amount of phosphorus had not. Fertilization can improve water effiency and increase wheat yield. The amount of increase in wheat yield by fertilizer can be arranged as follows: with high rainfall year larger than year with medium rainfall larger than year with low rainfall. In different rainfall years(355 mm/a, 411 mm/a, 523 mm/a), when wheat yield is highest, the amount of nitrogen and phosphorus are N 64.5 kg/hm², P₂O₅52.55 kg/hm²; N 127.5 kg/hm², P₂O₅105.0 kg/hm² and N 192.0 kg/hm², P₂O₅157.5 kg/hm² respectively.