Crop Water Use and Crop Coefficients of Maize in the Great Plains

Maize water use was measured by water balance in a 6-year field trial in the west-central Great Plains of the United States. Seasonal water use of the 102-day maturity class variety varied from 616 to 774mm, with an average of 666mm. About 10% of the seasonal crop evapotranspiration from the drip-irrigated crop was estimated to be evaporation from the wet soil surface following precipitation or irrigation. Seasonal crop evapotranspiration averaged 68% of tall (alfalfa) reference evapotranspiration and 82% of short (grass) reference evapotranspiration. Derived basal alfalfa-reference crop coefficients, Kcb, matched the ASCE Manual of Practice 70 (MOP #70) [Jensen, M. E., and Allen, R. G., eds. (2016). Evaporation, evapotranspiration, and irrigation water requirements, ASCE Manual of Practice 70, 2nd Ed., ASCE, Reston, VA] values fairly well during crop development, but mid-season values were about 1.05, which exceeded MOP #70 values by about 10%. Short reference Kcb values matched MOP #70 {and Food and Agricultural Organization Irrigation and Drainage Paper #56 [Allen, R. G., Pereira, L. S., Raes, D., and Smith, M. (1998). Crop evapotranspiration: Guidelines for computing crop water requirements, FAO Irrigation and Drainage Paper 56, Food and Agriculture Organization of the United Nations, Rome.]} recommended values fairly well. The derived basal crop coefficients were linearly related to crop canopy ground cover, which provided an excellent way to scale Kcb during both the crop development and maturation stages.