Suitable Method For Estimating Irrigation Water Requirement Of Winter Wheat

The northern main production area of winter wheat is selected as research object in this Dissertation. The effects of different time scales on estimated ET0, and the effects of different methods of dealing with the crop water requirement and effective precipitation, and the surplus precipitation on estimated irrigation water requirement(IWR) under different probabilities are analyzed comprehensively with Penman-Monteith equation, water balance equation, hydrological frequency analysis method and long series of meteorological data from NMIC. The main results are as follows:(1) Time scale has a significant impact on estimated ET0. The deviation of estimated ET0 increases with the increase of time scale, compared with the estimated results under daily scale. Dekad scale is recommended for ET0 estimation with agricultural purposes, by considering comprehensively the accuracy, meteorological data demand and agricultural irrigation management demand.(2) The effects of time scale selection on estimated ET0 showed good consistency in northern main production area for winter wheat, and the deviation of estimated ET0 under different time scales has no significant changes with latitude and longitude changes. It may be deduced that the geographic position is not needed to be considered for selecting appropriate time scale for ET0 estimation.(3) While estimating dekad irrigation water requirement of winter wheat with typical year method and probability analysis method, the estimated IWR with probability analysis method is significant lower than that with typical year method under lower guarantee rate, but significant higher under higher guarantee rate, no matter based on dekad IWR database or on dedad crop water requirement database and effective precipitation datebase.(4) Compared to the estimated IWR values for four typical guarantee rates with method in that surplus precipitation in a dekad have no affects on estimation of irrigation water requirement in following dekads, the IWR value, which was estimated with method in that subsequent utilization of surplus precipitation was considered, are less, no matter with typical year method or probability analysis method.(5) Considering subsequent use of the surplus precipitation will decrease estimated IWR values under the four typical guaranteed rates, and reduced values are significantly positive correlation with precipitation. Research results show that in the northern part of North China Plain where the precipitation is less, dealing with the surplus precipitation has little effect on estimated IWR. However in the southern part of the North China Plain where precipitation is more, the way of derling with surplus precipitation has significant effects on estimated IWR, which indicated that more attention should be paid for dealing with the surplus precipitation while estimating IWR for winter wheat.