Wheat water balance and its distribution in Gansu province
甘肃省小麦水分平衡及其时空分布模式

Gansu province located in northwest China has an arid and semi-arid climate with an annual mean precipitation of 40800mm.Deficiency of water resources has become the major factors restricting the agricultural development in Gansu province.Using field water balance model,monthly field wheat water balance has been estimated for 80 counties in the province for a period of 1960-2001.Deficit ratio and frequency were adopted to analyze spatial-temporal distribution of field water resources balance.The results show that under normal precipitation condition,rainfall cannot meet water demand for wheat,and that water deficit is the main character of field water resources balance in Gansu.Deficit of field water resources tends to increase from southeast to northwest,and from mountains to basins,varying significantly among the counties studied.Results show that water demand for winter wheat is 464.47 mm,the corresponding water deficit is 144.42 mm and the surplus water is 3.75 mm.As for spring wheat,water demand is 443.83 mm,the corresponding water deficit is 262.87 mm and the surplus water is zero mm.Water deficit of spring wheat is higher than that of winter wheat.Deficit water reaches the largest amount in May and July for both types,but the stability of water deficit for winter wheat is lower than spring wheat.For winter wheat,the highest frequency of water deficit is media,while it is more severely for spring wheat.