NEW MEXICO CLIMATE CENTER

New Mexico Crop Information

Alfalfa coefficient(k) to calculate evapotranspiration(ET) where Et=k*Eto

Eto = reference evapotranspiration or potential evapotranspiration referenced to grass.

Crop Coefficients use growing degree days (GDD) accumulated from planting based on the averaging method of calculating GDD with a maximum temperature cutoff of 999 C and a minimum cutoff temperature of -999 C. The Base Temperature is 5 C.

The equation for the crop coefficient (k) is: k=4.05E-1 +1.11E-3 Gdd -4.25E-7 GDD^2+3.56E-11 GDD^3 with an R^2=0.70 based on data from Artesia ,Clovis, Farmington, Las Cruces NM.The crop coefficient equation is appropriate for a flood irrigated crop with alfalfa yield around 20000 kg/ha at 0.0 moisture content.

The reference for this work is Sammis T. W. , C. L. Mapel, D. G. Lugg, R. R. Lansford , J. T. Mc Guckin 1985. Evapotranspiration Crop Coefficients Predicted Using Growing Degree Days ASAE 28(3):773-780