Synopsis
Yield depressions of 10 to 35% in irrigated spring wheat resulted from severe soil moisture stress. Reductions were greatest when stress was imposed during or after heading. Grain yield responses to nitrogen were due largely to increased head population. There appears to be no benefit in the irrigation of spring wheat prior to the boot stage unless moisture stress as indicated by wilting or curling of leaves is observed.
The 93-square-mile experimental watershed in Reynolds Creek is aimed toward the solution of water yield, flood flow, and sedimentation problems of the plateau and foothills grazing areas of the northwest. This watershed was selected in 1960 specifically to permit experimental isolation of the several factors affecting the well-known water balance equation. Basic networks for measurements and compilation of inventories of soils, vegetation, surface geology, and topography have been substantially completed. Detailed studies on small, simple watersheds with identifiable characteristics will provide basic understanding of hydrologic processes, which can be tested on the larger, complex subwatersheds of the Reynolds Creek basin. Watershed, Tucson, Arizona; (2) Southern Great Plains Itydrology Research Watershed, Chickashg; Oklahoma; (3) North Central Itydrology Research Watershed, Columbia, Missouri; (4) Southeast Itydrology Research 407 408 ROBINS, KELLY, AND YIAMON Watershed, not yet established; and (5) North-"east Itydrology Research Watershed, not yet established. PROGRAM OBJECTIVES AND RESEARC• APPROAC•
SYNOPSISYield reductions of about 20% under visible moisture stress were measured in Washington state. Causes were as follows: reduction in number of pods before blooming; reduction in number of pods and number of beans per pod during blooming; and reduction in bean weight during ma(uring process. Plant development was retarded by stress before blooming and hastened during blooming and maturing. Irrigation before visible moisture stress appeared to offer no advantage.
Conservation of moisture under field conditions using black, polyethylene film and soil ridging was studied during a 2-year period. Corn, in 42-inch rows, was used as an indicator crop. Results show a minor surface ridge, 90% film-covered, to be effective in conserving moisture and increasing yield and water use efficiency. Results also indicate that ridges without covering may conserve moisture. Subsurface barriers were not effective in moisture conservation or in increasing yields under the conditions studied. Good performance of the covered surface ridges is attributed to increased soil temperature in the spring, better utilization of light rains and suppression of evaporation losses. Supplementary laboratory studies of covered surface ridges substantiated the reasons given for improved moisture conservation.
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