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nDn:i'1" - 5 - specific minerals or compounds and the rates at which they may enter ground waters. Conflicting with the danger of ground water pollution, is the need for application of additional irrigation water beyond plant growth needs to avoid the accumulation of excessive amounts of salts in the root zone. The ~inerals applied in irrigation water will accumulate unless the soil is p~riodically flushed of salts. Although the total mineral content varies from a low to high salinity hazard from farm to farm in the Blue River Basin, the aver- age would be in the medium ranGe. This cal13 for a leaching require- ment of 10-15 percent additional water above crop requirement. This may be provided by precipitation m03t years but added irrigation wa- ter may be needed for this purpose. This would occur when rainfall plus irrigation is only equal to or less than the water needed for crop requirement plus the 15% leaching requirement. An alkali hazard may also exist in localized areas such as cen- tral Saline County. Chemical amendments with additional leaching May be needed to counteract this problem. On these farms it may be nece- ssary to aF-ply 30~ more irrigation \.:atel' to meet leaching needs. \1A TER USES Most row crops will use from 23-)111 net water through harvest in the evapotranspiration process. would be supplied partly by effective rai~fall and irrigation water. from planting time This requirement the remainder by Research by the Agronomy Department, University of Nebraska, showed an increase of crop consumptive use of approximately III of additional water when adequate fertilizer was applied for maximum yields of corn, grain sorghum and wheat. This increased crop con- sumptive water use, however, is more than offset by the increased efficiency of soil water in producing crain as shown in Table 3. Table 3 NEAN C"IT PRODUCTION PER INCH 0,' \'IA r?:R COl1SUNPTIVELY BY CROP No Fertilizer Fe!'tilizer Applied % Yield Increase Corn 2,98 cwt. 4,26 cwt. 43 Grai n Sorghum 2.99 3,81 28 Wheat 1.41 1.58 12 Good fertilizer p!'Bctices means more cwt of grain from the water applied and is therefore a good practice for gaining the most benefit from our water resources. The research on which Table 3 is based alse showed that additional water was needed when the crop was adequately fertilized. One additional inch of water, for example, was required to increase the yield of corn from an average of 91 bushels to 133 bushels per acre. Nebraska agricultural statistics show that in 1965 average yields of irrigated corn were 96 bushels in the East and South regions.