Field investigation was carried out in the experimental station,Institute of Wheat and Potato in Heilongjiang,124°50′E,48°2′N.The experiment soil belongs to the classification of chernozem.The located site is of a typically heavy frigid climate,an annual mean temperature of 1 3℃,ranging from -42 0 to 38 0℃,an annual mean precipitation of 508 2mm,with 52 6% falling in July and August,and an mean annual evaporation of 1189 7mm.The sample of soil was taken from long-term fields rotating with wheat and so...