| Crop coefficient is an important parameter for calculating crop water requirements and reasonable distribution of irrigation water and water resources. According to the observated records from 1991 to 2011 in 10 typical agricultural meteorological stations of Heilongjiang province, the average soybean growth stages were determined by using the statistical method, the crop coefficients of soybean were estimated by using the FAO recommended Penman-Monteith Formula and water balance equation in root zoon, and the variable rule of crop coefficient of soybean was further analyzed. The results indicated that: In recent 20 years, the sowing date of soybean was delayed average 5 days, the harvest date was delayed 10 days, and the average soybean growing season was from first day of May to last day of September. The soybean crop coefficient displayed unimodal distribution in whole growing season. The average crop coefficient in whole growing season was 0.61, the highest value was 0.96 at podding stage, the second was 0.75 at flowering stage, the lowest value was 0.32 at seedling and maturing stages. The crop coefficients in three leaves stage, branching stage and poddring stage were 0.60, 0.62 and 0.71, respectively. The water sensitive period was podding stage and flowering stage. |