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Irrigation requirements for alfalfa in the Nicola Valley Willcocks, Timothy John

Abstract

The Nicola Valley, in the dry interior of British Columbia, is an important cattle ranching area. Alfalfa and grass hay are grown to provide winter feed for the cattle, but due to the low annual precipitation (9.5 ins. at Merritt) and high rate of evapotranspiration, irrigation is necessary. Of the licenced water supply, 95 percent is licensed to agricultural use. In this study, which is of the reconnaissance type, current irrigation practices within the area are described, and on the basis of available data and some field measurements, a method is developed from which irrigation and drainage requirements are determined for several typical locations. Seasonal evapotranspiration was estimated from readings obtained from an Ogopogo carborundum block evaporimeter, and for Merritt, Douglas Lake, and Quilchena, seasonal requirements were found to be 26, 19, and 24 acre ins./acre respectively. The leaching or drainage requirement was found to be low in the Nicola Valley. A local maximum value of 8.3 percent was found, but drainage water not exceeding one percent of consumptive use was estimated for an average season. It was considered advisable to add gypsum to irrigation waters in certain cases to prevent sodium alkali soils from developing; the more usual tests indicating sodium hazard gave unsatisfactory results. The concept of efficiency of water use requires some careful definition: it is pointed out that present definitions of water efficiency can be misleading. Conveyance efficiencies were found to be highly variable with seepage values of 8 percent to 96 percent per mile; efficiency of distribution of irrigation water within a field was taken from comparative data.

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