CRDSS_Task1_14-15_Penman-Monteith Equation

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To solve the above problem and the missing Kc values for some crops required in the CU model crop type list, it is assumed that some general similarity in the crop characteristics and seasonal growth dates can be applied to estimate the absent crop Kc values. These assumptions imply that some crop Kc values are equal and can be used for the same KC categories. These are : Spring Wheat=Barley =Spring Grain Winter Wheat= Fall Wheat Dry Beans=Snap Beans=Green Beans Corn=Corn Silage=Corn Grain=Sweet Corn Hill Pasture Grass= Grass Pasture= Meadow Harvest Grass=Sod Farms or Lawns Orchard with Covers= Orchard without Covers It should be noted that the lacking references for crop coefficients can be filled in the future for each Kc category whenever this data is available for the area. The basal reference crop coefficients for an alfalfa base given in Table 1 shows six different crop types. These values have been taken from Jensen et al. (1990). Figure 1 shows the plot of these data with respect to the series number. The plot gives the general trend for the Kc values for different crops, and the series number does not represent the days from planting date. Table 1 should be used to determine exactly the growth period in days for each series point of interest shown in Figure 1. The same thing is true for all other tables and figures given in this section. Table 2 and Figure 2 also give the basal crop coefficient values but for a grass base. Tables 3 and 4 and Figures 3 and 4 show the mean crop coefficient for an alfalfa and a grass base given respectively, which was modified and adapted for the Gunnison River basin by the CRDSS CU team. Reference Crop Routines Some of the routines in the CU model for the PM equation were developed by W.W.Wheeler and Associates. The PM equation is based on a standard alfalfa and grass reference crop equation as presented in Jensen et al. (1990). 3.0 CONCLUSIONS AND RECOMMENDATIONS The CU model uses the PM equation in computing reference crop ET in the Gunnison River basin. This equation required crop coefficient curves for each crop in the model. To determine the derivative of experimental crop coefficients is complex and time consuming process. The CRDSS CU team adopted and modified basal and mean crop coefficients for both an alfalfa and a grass base in the Gunnison River basin using the local crop growth data. The original Kc values were published in the engineering field; most of these data were given in Jensen et al. (1990). 4 A 275 01.09.95 1.14-15 Al-azzawe