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F . . HUUCATION <br />Prepared by James Barnhill, Weiser County USU Extension Agricultural Agent <br />Nothing will affect production in a management plan more than providing adequate irrigation. Different soil types hold <br />various amounts of water. Once gravitational water has flowed out ofa saturated soil, it is at geld capacity " (the capacity ofthe <br />soil to hold moisture is full). The "wer plants can extract & called available water: However, by rite time all the available water is <br />used, the plants are dead .about hatfaf the water in a soil at field capacity is held so tightly that plants cannot extract it. That half is <br />called unavailable water. To avoid plant stress, irrigate when half of the available soil water is used up. <br />sort, WATFIn <br />- Field Capacity <br />( Irrigate to prevent plant stress <br />- Plants die <br />- No water left in soil <br />Nvheit to irrigate? <br />In all soils other than sand, a rough check on soil <br />moisture can be done using the Soil Ball Method. <br />Dig a small hole and remove a handful of soil from 6 <br />to 12 inches deep. Squeeze the soil into a ball. Then, <br />open your hand and bounce the ball (in the palm of <br />you .hand). If it remains in a stable shape, the soil has <br />more than 50 percent of its available water. If it <br />crumbles, it needs irrigation. <br />How>iong to hvigate3 <br />In general, irrigate clay soils for longer periods, and <br />sandy or rocky soils for short periods. Soils with a <br />finer particle size, like clay, hold more water than <br />coarse soils, like sand. It takes approximately 1 inch <br />of water to refill one foot of clay or loam soil. It only <br />takes 0.5 inches of water to recharge a foot of sandy <br />soil. <br />Knowing the application rate or soil intake rate are <br />important in calculating how long to run the irrigation <br />system. <br />Sprinkler: To determine the application rate of a <br />sprinkler, place straight-sided containers under the <br />sprinkler system for an hour, then average the depth <br />of water in the containers. From this the inches/hour <br />can be determined. Periodically check sprinkler <br />uniformity. <br />.f=lood: To estimate the amount of water absorbed per <br />hour under flood irrigation, refer to the intake rate for <br />the particular soil type as listed in Table 1. <br />The length <br />a <br />of time the <br />irrigation <br />system runs <br />will <br />determine 1.4 <br />how much av <br />Water is <br />f ?rw <br />applied. <br />There is no ,4 <br />point in <br />filling the soil profile with water to a depth greater <br />than the crop roots can reach. <br />Table 1. AVAILABLE WATER <br />SOIL <br />"T'EXT'URE WATER AVATI .ABLE FOR UtiE <br />::.BETWEEN IRRIGATIONS <br />(501 OFAVAILA13LEWATER) INTAKF. RATE' <br />'.INCIIESI <br />IIOUR <br />Sand 0.5 inch/.foot 1.0-3.0 <br />Loam 1.0 inch/foot 0.3-0.8 <br />Clay 1.0 inch/foot 0.01 - 0.2 <br />Adapted from: S ri? inklers, Crop Water Ilse and <br />Irrigation Time. Weber County, Utah State <br />University Extension, ENGR/BIE/W W 14, April <br />2001. <br />'Normal ranges. Intake rates vary greatly with soil <br />structure and structural stability. <br />61