Study On Measuring Crop Evapotranspiration And Crop Coefficients Changes For Winter Wheat And Maize

ET is an important element for estimating irrigation water requirements and in waterresource management. It is of great significance in the agricultural production. In this paper,the calculation of crop evapotranspiration (ETc) and crop coefficient (Kc) of winter wheat andmaize was conducted with data obtained through large-scale weighing lysimeter undersufficient water supply. While combined with the experimental data between1998and2011, aregulative formula was discovered which can be representative of the semi-arid andsemi-humid district. The results can provide reference to the studying on the irrigationagriculture in the arid and semi-arid region of in the loess plateau. The main results are asfollows:(1) The reference crop evapetranspiration of winter wheat is400～460mm and thereference crop evapetranspiration of summer maize is330～410mm.The results show thatreference crop evapetranspiration has positive correlation with temperature (T),radiation (Rn)and sunshine (N). Rnis the most influential factor, following by sunshine and temperature.Linear relation was found between ET0and Rn, exponential relationship between ET0and T aswell. Reference crop evapetranspiration has no obvious positive relation with windspeed.Furthermore, a negative relative relationship is found with relative humidity.(2) Crop evapetranspiration of winter wheat during crop growing stage in Guanzhongregion is350mm～450mm with the average near407mm.The crop evapotranspiration ofwinter wheat in terms of growing periods exerts the feature with two summits insowing-tillering and heading-filling period respectively. It can also be concluded that cropevapotranspiration is proportional to the irrigation and the rainfall as well.(3) Crop evapetranspiration of summer maize during crop growing season in theGuanzhong region is400mm with an average about343mm. Maize's ETchas show a singlesummit relation occurred during heading to grain filling stage with water requirement.Thelowest ETc is during Planting-jointing stage while the least water is needed in grouting-harvest stage.(4) Diurnal variation of soil evaporation was similar to diurnal variation of fieldevapotranspiration. The peak occurred between12:00and14:00o'clock. Soil water content in the0-10cm layer has relatively obvious changes, and the larger depth the milder is thechanges. Curves of evapotranspiration and crop coefficients have same change trend with soilwater content's. There exists quadratic correlation between evapotranspiration and leaf areaindex, and linear correlation between evapotranspiration and leaf area index. Evaporation isinversely proportional to the leaf area index and showed a power function relationship.(5)The two summits of the winter wheat coefficient are observed in the periods oftillering-overwintering and heading-filling.The summit of the crop coefficient is observed inthe period of heading-filling. The results showed that crop coefficient has good second-orderpolynomial,third-order polynomial,and logarithmic relationship with cumulative growingdegree,day after planting,and leaf area index,respectively.