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<br />C) <br />'::'1 <br />~ <br />Q') <br />-.,J <br />W <br /> <br />"the whole area. <br />in surface inflow <br />drains during the <br /> <br />This is explained by the difference <br />rates across the area between <br />two stages. <br /> <br />"Comparison of continuous ponding with alternate <br />ponding and draining shows that in the latter case <br />complete desalinization is achieved with consider- <br />ably less leaching water. The leaching efficiency <br />is not very high under continuous pondlng." <br /> <br />Robinson and Luthln (1967) concluded that intermittant flooding was more <br />effIcient in terms of salt removed per unit of water applIed but took longer <br />to leach a given soil sarea than did the continuous ponding. Unpublished <br />data of Malek Kaddah, Soil Scientist at Imperial Valley Conservation Research <br />Center, ARS, Brawley, showed that leaching could reduce surface salts from a <br />range of 15 mmho/cm to a range of 3-4 mmho/cm and that wi thin 2 years the soil <br />was back to its original salt content. <br />Sprinklers can be used to good advantage for leaching. Wilson and Luthin <br />(1963) noted that rainfall was more effective than ponding for leaching. <br />Nielsen, Bigger and Luthin (1965) noted that sprInkling was more effective <br />than pondlng in salt removal. Collis~George and Laryea (1971) note that <br /> <br />"When unstable soi I moisture potential is 0 or near <br />0, the structure collapses greatly reducing and the <br />movement of the wetting front and infiltration rate <br />are small compared to a stable soil. <br /> <br />"The infi Itration behavior of unsaturated soi Is <br />with restricted supply rates which do not develop <br />surface ponding is similar to that of structurally <br />stable materials under the same restricted supply <br />rate, in that the structure is not destroyed." <br /> <br />Robinson et al. (1968) noted that bulk densities of Imperial clay soils <br />remained 1~1o lighter under sprinkler irrigation that under flood irrigation. <br />The seed bed granulation remained under the sprinklers, but broke down during <br />flooding. Where sprinklers are available for non-ponding rates of application, <br />they will be of advantage. <br />Kovda (1973) presents a concept of leaching after each 20 irrigations <br />with a 1,000 ppm water. The leaching would drop the soil salinity to one- <br />half its value, i.e., when soil which initially contained 0.2% salt was <br />allowed to increase to 0.4% salt, a 1,000 ppm irrigation water would then <br />have a leaching phase to drop the water to 0.2% again. <br />Operators which are utilized In the agricultural operations of Imperial <br />14 <br />