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002703 establishing irrigation schedules. In marginal operations, the farmer's resources are too meager to cope with the difficult problems common to irrigation in arid regions. Good management generally results in high yields. Two crops per year are common in many irrigated areas though double-cropping is limited in some places by iate..eason water shortages. About 33 percent of the irrigated acreage is adequately managed, with onfarm measures to increase production and conserve water. On the irrigated land, the major crops are feed grains and hay, vegetables, cotton, and citrus and other fruits. Dryland farming, with about 3.3 million acres cultivated in 1965, has reached or passed its peak. The small grains, grasses, and other crops traditionally produced this way can be produced more profitably under irrigation. While production from dryland farming is at a higher level per acre than it was in earlier days, largely because of technological advances, it is still subject to improvement. Crop production generally is an exclusive land use except where hunting may be permitted and livestock used to harvest certain crop residues. Needs and Problems - Crops On irrigated land the major problems, exclusive of water supply, pertain to water distribution and maintenance of soil fertility. Under the common furrow or border irrigation methods, water tends to pond temporarily unless grades and lengths of runs are adjusted to soil conditions and to the rates of water application. Where ponding takes place, salt in the soil rises to the surface and depresses crop yields. Waterlogging also may occur in the soil profIle with the same depressing effect over a longer time. Sometimes seepage from canals also results in waterlogging. Maintenance of soil fertility on both irrigated and dry .farmed land is much less of a problem from the nutrient standpoint than it was before commercial fertilizers became easily available. Under intensive cropping, soil structure or tilth still deteriorates unless organic matter is added. Satisfaction of the projected needs for the products of agriculture will require that more land be irrigated but will permit a small reduction in the acreage farmed without irrigation. Current and projected needs for irrigated and nonirrigated cropland are shown in figure 37. Plan Response - Crops The framework plan provides for the installation of onfarm measures for crop production improve- ment on the following acreages: 18 16 14 (f) 12 w 0: U <t 10 "- 0 (f) z 8 Q ..J '" :;; 6 4 2 0 LanJ Management ./"'" / V IRRIGATED LAND / ~y FARMED LAND 1965 1980 2000 2020 Figure 37 .-Land needs for crop production. 1966.1980 1981-2000 2001-2020 . 12.8 million acres .12.5 million acres . 9.7 million acres For irrigated land, the various measures for better water distribution include lining of onfarm ditches; land leveling, and releveling; as well as changes from one irrigation method to another - furrow to sprinklers, for example. Improvement in the shaping of ridges between furrows will protect seed against salt accumulations that develop at the soil surface as evaporation takes place. To avoid erosion, surface disposal systems will be provided to handle excess rain or irrigation water. Onfarm subsurface drainage measures, including drain tile, are provided where water table problems exist or will develop under expanded irrigation. Soil fertility and structure will be maintained or improved through cover cropping and crop rotation. Dry .farm lands are protected from erosion through such measures as contour cultivation, fall chiseling, stubble mulch tillage, and installation of diversion ditches and grassed waterways. Grain-fallow rotation and improved cultural operations to conserve 89