| The paper introduces the ratio to mutually transform between the reference evapo-transpirations by FAO-recommended Hargreaves formual and by Penman-Monteith Formula, then uses Hargreaves formula and Penman-Monteith Formula to calculate the crop evapo-transpirations during various growth periods with the 19-year meteorological data measured by the Experiment Station of Irrigation of the Northwest A&F University, and late on determines the empirical coefficient of Hargreaves formula through analysis. The experiences prove that the result is reliable and feasible for production practices. |