Table 5.3 k, and k₂ values to be used in Blaney-Criddle formula (Blaney, 1959) Grow. k₂ (% of k₁) Crop Seas. k₁ Mar. Apr. May June July Aug Sep Oct Nov (mo) Alfaalfa Year 0.85 Citrus Year Decidius Year Grass Year 0.75 2227 70 120 108 114 125 113 108 68 70 93 82 100 98 100 93 93 145 93 29 94 102 154 148 114 90 75 65 44 100 116 132 124 128 128 88 56 Cotton 7 0.65 45 75 100 130 150 Sugar beet 5.5 0.70 53 75 153 242 192 100 42 28 888 Tomato 4.5 0.60 70 122 115 140 Com 4 0.80 46 146 162 100 38 Beans 3 0.65 37 70 165 127 Cereals 3 0.80 102 153 118 24 Potato 3 0.70 75 85 140 110 Sm.Grains 3 0.75 102 153 118 24 Rice 3.4 1.10 30 125 133 131 135 48 Table 5.4 P values to be used in Blaney-Criddle formula (Criddle, 1958) N R T H L A T I T U D E S Mon 24° 26° 28° 30° 32° 34° 36° 38° 40° 42º 44° Jan 7.58 7.49 7.40 Feb. 7.17 7.12 7.07 Mar, 8.40 8.40 8.39 8.38 7.30 7.20 7.10 6.99 6.87 6.76 6.62 6.49 7.03 6.07 6.91 6.86 6.76 6.73 6.65 6.58 8.37 8.36 8.35 8.34 8.33 8.31 8.30 Apr. 8.60 8.64 9.68 8.72 8.75 8.80 May 9.30 9.38 9.46 9.53 9.63 9.72 June 9.20 9.30 9.38 9.49 9.60 8.85 8.90 8.95 9.00 9.05 9.70 9.81 9.92 10.02 10.14 10.26 9.83 9.95 10.08 10.21 10.38 Sep. July 9.41 9.49 9.58 9.67 9.77 9.88 9.99 10.10 10.22 10.35 10.49 Aug. 9.05 9.10 9.16 9.22 9.28 9.33 9.40 9.47 9.54 9.62 9.90 8.31 8.31 8.32 8.34 8.34 8.36 8.36 8.38 8.38 8.40 8.41 Oct. 8.09 8.06 8.02 Nov. 7,43 7.36 7.27 Dec. 7.46 7.35 7.27 7.99 7.93 7.90 7.85 7.80 7.75 7.70 7.63 7.19 7.11 7.02 6.92 6.82 6.72 6.62 6.49 7.14 7.05 6.92 6.79 6.66 6.52 6.38 6.22 The Blaney Criddle method (Blaney and Criddle, 1950; Criddle, 1958) is widely used to determine Potential Evapotranspiration in arid and semi-arid zones. In this method, consumptive use is given as follows: U =25,4 kf (5.10) Where U: Potential evapotranspiration in mm/month k k₁ *k2 monthly crop coefficient k₁ Seasonal coefficient k2: Monthly coefficient as % of k₁. (k₁ and k₂ values are given in Table 5.3 for different crops and months). f: Climatic factor f= 1.8t 32 100 P (5.11) t: Mean monthly temperature in °C p: Monthly daytime hours as a percentage of the annual value, given in Table 5.4 as a function of the latitude of the place and the month of the year. Problem 5.8. The following crops (Table 5.6) will be planted in a new agricultural area where irrigation water will be obtained from a newly found groundwater source. Mean monthly precipitation and temperature values are given in Table 5.7 for an average and also for the driest year for this area, which lies at 34°N latitude. Compute the consumptive use for each month then determine the necessary irrigation amount for an average and also for the driest year. Table 5.6 Information about the planted crops for Problem 5.7 Growing season (month) Crop Area (ha) Corn 100 June - Sep. Small grains 50 March - June Tomato 70 July - Sep. Potato 100 June-Sep. Cotton 200 June - Sep. Table 5.7 Temperature and precipitation data for Problem 5.7 Month June March April May Meant (°C) Pave (mm) Pariest (mm) July Aug. Sep. 12.3 15.7 18.2 21.3 22.4 21.6 16.8 18.5 23.4 15.2 7.3 3.1. 1.3 8.9 12.3 6.2 8.7 3.1.