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<br />1 infiltration occupies a significant portion of the time. Crop roots can <br /> <br />2 then absorb the water as it goes by. With infrequent irrigation, a <br /> <br />3 large quantity of water is stored during a short time. For this stored <br /> <br />4 water to be used, it must be brought into contact with active roots. Th <br />L <br />5 only way this can take place is for the soil near the~Toots to drysuf- <br /> <br />6 ficiently to establish a sizable hydraulic gradient. But, as the soil <br /> <br />7 dries, hydraulic conductivity decreases precipitously -- as much as <br /> <br />8 several thousandfold. <br /> <br />[See Rawlins (4) and Rawlins and Raats (3) for a <br /> <br />9 detailed theoretical analyses of this process.] The larger the quantity <br /> <br />lG vi water stored in the scil profile, the deeper it will extend beyond <br /> <br />11 the active roots, and the longer and more severe the drying period must <br /> <br />12 be to bring it back to the roots. This drying can seriously reduce crop <br /> <br />13 growth. <br /> <br />If the soil is not permitted to dry long enough to allow this <br />I <br /> <br />14 water to be pulled back to the roots and used, the remaining water is <br /> <br />15 simply flushed out the bottom of the root zone when the soil's water <br /> <br />16 stDrage capacity is refilled by the next irrigation. By supplying the <br /> <br />17 crop's water heeds on a frequent basis, water need not be stored deep <br /> <br />18 ,~tt~n the profile, and the long extraction process can be avoided. As <br /> <br />19 a consequence, the average soil water content remains far higher, even <br /> <br />20 with very low deep percolation, than it do~s with infrequent irrigation. <br /> <br />21 This constantly high soil water content is ideal for maximum growth of <br /> <br />22 most crops. It eliminates drought-induced yield reductions and keeps <br /> <br />23 solutes contained in the irrigation water diluted. <br /> <br />24 lfuether water is actually saved with high-frequency 'irrigation, <br /> <br />25 depends on how closely the irrigator matches the quantity of water <br /> <br />26 applied to the crop's needs. Considerable progress has recently been <br /> <br />G,,~C";Q <br />27: r::ade in the use _ of c:limatological data to sch2dule irrig~"'t_o'r( 'off 3. '("ide J <br />