Crop Coefficient

Pinto Beans Coefficient(kc) to calculate evapotranspiration(ET) where Et=kc*Eto

Eto = reference evapotranspiration or potential evapotranspiration referenced to grass.

The Pinto beans crop coefficients are from a lysimeter study with a yield of 4100-5300 kg/ha. See Figure 2 for yields of 3000-3500 kg/ha. The crop coefficient of 1.6 is high compared to literature values.

Figure 1

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 10 C. The Base Temperature is 10 C.

The equation for the crop coefficient (kc) is: Kc =5.16E-01 - 3.47E-03(GDD) +1.27E-05(GDD)2 - 8.42E-09(GDD)3 with an R^2=0.9 based on data from Farmington NM. The crop coefficient equation is appropriate for a pinto beans field with a yield around 41000- 5300kg/ha.

Figure 2

The equation for the crop coefficient (kc) is: Kc =1.96E-01 - 2.12E-04(GDD) +5.72E-06(GDD)2 - 4.77E-09(GDD)3with an R^2=0.50 based on data from Farmington NM. The crop coefficient equation is appropriate for a pinto beans field with a yield around 30000- 35000kg/ha.

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

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