Water Production Function
Barley Water Production function or the relationship between Evapotranspiration and yield
Et = evapotranspiration or water used by crop.
The water production function has grain yield expressed in kg/ha at 14.0 % moisture content.
The water production function is y= -2107+142.8 Et . The coefficient of determination is 0.83
The reference for this work is Kallsen, C. E. , T. W. Sammis. E. J. Gregory. 1984. Nitrogen and Yield as related to water use of spring barley. Agronomy Journal 76:59-64
Barley coefficient(kc) to calculate evapotranspiration(ET) where Et=kc*Eto
Eto = reference evapotranspiration or potential evapotranspiration referenced to grass.
Crop Coefficient uses growing degree days (GDD) accumulated from planting based on the averaging method of calculating GDD with a maximum temperature cutoff of 30 C and a minimum cutoff temperature of 5 C. The Base Temperature is 5 C.
The equation for the crop coefficient (kc) is: kc=5.70E-2 +3.23E-4 Gdd +3.94E-6 GDD^2-3.26E-9 GDD^3 with an R^2=0.93 based on data from Farmington NM. The crop coefficient equation is appropriate for a barley field with a yield around 7000 kg/ha. The point with a kc of 1.6 was not included in the regression analysis.
The reference for this work is Kallsen, Graig E., E. J. Gregory, T. W. Sammis. Oct. 1982. Water -Use production functions of selected agronomic crops in northwestern New Mexico, Phase II. New Mexico WRRI report No. 155
Climate data should be copied from web site using Netscape. If you use Explorer, copy climate data to Notepad and then copy from Notepad to spreadsheet. Click on part of picture for instructions on how to fill out spreadsheet. A copy of the spreadsheet has been developed that uses Samani's equation for potential evapotranspiration requiring only temperature data.
Climate data should be copied from web site using Netscape. If you use Explorer, copy climate data to Notepad and then copy from Notepad to spreadsheet. Click on part of picture for instructions on how to fill out spreadsheet.