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In scheduling of irrigations it has been customary (1, 2, 3, 4) to credit the soil moisture balance sheet with the depth of irrigation water received and retained by the soil. This depth is usually calculated as (a) a stated percentage of available soil moisture to effective root depth, or (b) the depth of evapotranspiration occurring during an irrigation interval. In practice, these two methods should give essentially the same answer. Credit for an irrigation is entered at the start of the irrigation (2). As previously reported (5), very low balances and soil moisture con tents were found in the latter half of an orchard being irrigated. Before each irrigation was started the balance at the first setting was allowed to lessen to a value representing about 50% available moisture. At semi-arid sites this usually produced balances of less than 50% available water at the last setting of the line, sometimes as low as 20%. Excessive Irying in the second half of the orchard was found to be caused by fluctuations in the weather. The optimum range of soil moisture in orchards was found to be between 100% and about 40% available water.
credit to give for an irrigation when scheduling irrigations
Wilcox, J. C. 1970. CREDIT TO GIVE FOR AN IRRIGATION WHEN SCHEDULING IRRIGATIONS. Canadian Agricultural Engineering 12(1):28-32.
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