2018-10-16_PERMIT FILE - M2018039 (2)

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Table 2.Estimated seasonal water requirement(consumptive use)in western Colorado*(inches/season). Canon Monte City Cortez Durango Gunnison Fruita Meeker Vista Norwood Salida Walden Alfalfa 39.69 29.36 27.49 17.99 36.22 23.55 23.58 23.58 24.83 12.89 Grass hay/pasture 33.49 24.74 23.17 17.12 31.44 21.43 19.85 20.40 20.90 13.61 Dry beans 19.93 Corn,grain 25.12 Corn,silage 22.21 17.98 16.06 22.67 17.34 Corn Melons Orchards w/o cover crop 27.12 Orchards w/cover crop 25.71 Potatoes 16.49 Small vegetables 18.06 6.79 Sorghum,grain Soybeans Spring grains 13.51 14.79 16.73 19.61 15.46 12.66 11.38 18.04 (barley,wheat) Sugarbeets 31.58 Wheat,winter 18.70 20.13 18.83 18.95 Av.Precipitation 12.99 12.90 18.59 11.00 8.30 17.06 7.25 15.73 11.37 9.56 Av.Effective Precipitation 9.28 5.09 8.34 3.80 3.98 6.19 3.93 6.05 5.66 3.02 *Colorado Irrigation Guide,1988.Net irrigation requirement is the difference between crop consumptive use and effective precipitation. 0 80 percent of the ir- as compared to continuous corn,which o Wheat Corn Soybeans rigation required for is predominantly irrigated from June to Ez comaximum produc- early September. tion.The final option Crops such as corn,soybean and wheat N would be to raise 50 have different timings for peak water use percent of available (Figure 3).With low capacity wells,plant- acres to dry bean and ing multiple crops with smaller acreages 50 percent to corn allows for water to be applied at amounts CL C and maintain maxi- and times when the crop needs the water. May June July Aug. Sept. mum production on The net effect of irrigating fewer acres at v all acreage. any one point in time is that ET demand Figure 3:Example of daily ET during the of that crop can be better met.If capacities growing season. are increased by splitting acres into crops Limited Water that have different water timing needs, Limited Water Management - Low management can be done to replace stored Capacity Systems soil moisture rather than maintaining soil Management - When managing for maximum moisture near field capacity in anticipa- Reduced Allocations production,irrigation systems must have tion of crop ET since the system will not When producers are faced with reduced minimum capacities that meet crop water meet ET. surface water storage,they have three man- requirements during peak water use pe- Another option is to plant the entire agement options.They can: 1.)reduce ir- riods.(See Fact Sheet 4.704,Center-pivot pivot or field to a single crop.Irrigation rigated acreage,2.)reduce irrigation to the Irrigation Systems.)If irrigation system management with low capacity systems entire field,or 3.)include different crops capacities are below what is normally requires that a producer maintain soil that require less irrigation.Option 1 will required,reduced yields are expected with moisture at or near field capacity when idle potentially productive ground while normal precipitation.Management strate- ET is less than what the system can apply. option 2 will reduce yields for the irrigated gies to compensate for low capacity include When the ET for the crop is greater than acres unless precipitation is above normal. pre-irrigation and beginning irrigation at the capacity of the system,plants will Option 3 incorporates the use of crops higher soil moisture contents.These strate- use stored soil moisture to maintain ET. that require less irrigation for maximum gies may maintain yields in above normal This type of management is necessary to production to apply the"saved water"for precipitation years but do not help as much insure that moisture will be available for traditionally irrigated crops. in below normal precipitation years.Man- plants when they reach the reproductive An example in Longmont would be agement strategies to alleviate this problem growth stage.However,if precipitation is irrigating all corn or irrigating some corn include splitting systems into two or more less than anticipated,soil moisture may be and dry beans.Corn requires 17.3 inches of crops that have different peak water needs, less than 50 percent of available during the irrigation(85 percent efficiency)and dry thus reducing the rate of water require- reproductive growth stage and yields will bean requires 10.4 inches.If the alloca- ments during both peak periods. be reduced. tion from the ditch limits a producer to Crop rotations also spread the irriga- 14 inches of water,he or she could raise tion season over a greater time period as Colorado State University,U.S.Department of 80 percent of their acres to irrigated corn compared to a single crop.When planting Agriculture and Colorado counties cooperating. and the remainder in dryland production multiple crops such as corn and winter CSU Extension programs are available to all without or idle.They could also raise 100 percent wheat under irrigation,the irrigation sea- discrimination.No endorsement of products mentioned of available acres to corn and apply only son is extended from May to earl October is intended nor is criticism implied of products not pp Y Y Y Y mentioned.