Abstract
SummaryA field survey was conducted to determine the effect of salinity in irrigation water on the yield of orange trees (Citrus sinensis). The part of the survey reported here included 104 sampling sites containing the three variety-rootstock combinations Shamouti orange on sweet lime (Sh × SL), Shamouti on sour orange (Sh × SO) and Valencia orange on sour orange (V × SO). The multiple regression technique was used for the statistical analysis of the data.The analysis yielded multiple regression equations of yield (Y) on salt content of the irrigation water (Cw), soil moisture saturation percentage (SP), the product of the two (interaction term), and qualitative variables (region, tree age, and tree age × Cw interaction). Cw was expressed in terms of chloride (Clw), sodium (Naw) or sodium adsorption ratio (SARW). There was a highly significant correlation between Clw, Naw and SARW, and therefore it was impossible to isolate the effect of each component of salinity. The discussion is given terms of Clw.The regression equation for Sh × SL explained 78% of the variation in Y, in terms of squared deviations from the mean; 20% was due to regional and tree age effects and the rest was due to Clw and SP. Only 42% and 54% of the variability in Y was explained by the regression equations for Sh × SO and V × SO, respectively. Nevertheless, all regression equations had significant R2 values.In all cases the effect of soil texture as expressed by SP and the interaction of SP on Cw was highly significant. The higher the SP value was, the lower was the effect of salinity. For the mean SP value for Sh × SL, there was a yield decrease of 2.31 ton/ha (4.3%) per meq/l increase in Clw. For V×SO, the corresponding yield decrease was 3.25 ton/ha (5.5%) and for Sh×SO there was essentially no effect (actually a slight yield increase).
Published Version
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