Improving Irrigation in Eastern Oregon

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Developing new irrigation land generally presents some soil and irrigation management problems. Certain problems emerged on the Owyhee Project shortly after irrigation was initiated in 1935. Among these were high water use, low irrigation efficiency, low water intake rates, excessive surface runoff, and scattered nonproductive "slick spots." Similar problems exist on other irrigation projects. These problems were studied as a cooperative State-Federal research program beginning in 1946 and ending in 1953, except for observations and certain final tests made in 1954. Main results of the experimental plot research have been published in Oregon Agricultural Experiment Station Technical Bulletins 22 and 23. Results of farm field trials from 1950 to 1953 are presented in this publication. Recommendations for handling soil and furrow irrigation problems in this and other areas also are reported. "Slick Spots" a Problem: The problem - Irregular areas with poor or no plant growth are scattered throughout many fields. These areas are recognized easily in freshly tilled fields by their gray color, compared to the brown color of the surrounding soil. Water penetration is poor and crops suffer from water shortages during the warmer part of the season, even with frequent irrigations. Subsoils also contained adsorbed sodium which harms sensitive plants. The cause - The exact sequence of events is uncertain, but under an earlier influence of salts, sodium was adsorbed by the clay particles. The clay particles dispersed and moved downwards in the soil, leaving an ashy gray surface soil of low fertility and forming a clay layer in the subsoil which water and plant roots find difficult to penetrate. How to improve "slick spots" - Sodium must be removed from the clay particles and replaced by calcium to improve the physical condition so water and plant roots can penetrate. Research trials showed the best way to accomplish this change is a combined application of gypsum and manure. Gypsum supplies calcium to replace sodium from the clay, and manure temporarily improves the physical condition and water penetration. Straw, hay, and crop residues also can be used. Liberal amounts are needed. On trial plots, 50 tons per acre of manure and 16 tons per acre of gypsum were used. These rates aren't too costly because usually there is a relatively small total area of slick spots on any one farm. Work the gypsum and manure into the surface and plant a crop. A forage crop is preferred. If residues other than manure are used apply supplemental nitrogen and phosphorus. One hundred pounds per acre each of N and P205 (phosphate) are suggested initially. If the forage mixture does not contain a legume, additional nitrogen may be needed the second year. If straw is used, nitrogen will be needed both for decomposition of the straw and for crop growth. Watch carefully for nitrogen deficiency, and supply more nitrogen as needed. Frequent irrigation is necessary to wash out replaced sodium. Forage crops hasten the removal of sodium because they require more irrigations per season. Increase in organic matter and improvement in the soil's physical condition also will be more rapid with forage crops. Sulfur and waste sugar beet lime were tried but were not as effective as gypsum. In this soil, the calcium from lime application proved to be less soluble than from gypsum. Sulfur is most effective on calcareous soils. Slick spots in this area are calcareous only in the deeper substrata.

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ELECTRONIC FILE - BOTANY:OTHER

This bulletin reports cooperative research by the Oregon Agricultural Experiment Station; the Bureau of Reclamation, U.S. Department of the Interior; and the Soil and Water Conservation Research Branch of the Agricultural Research Service, U.S. Department of Agriculture. The latter now includes the U.S. Salinity Laboratory and the former Division of Irrigation, Soil Conservation Service, who participated.