Abstract

Widespread water deficit is expected to depress growth and yields of oil palms, which sustain daily losses of water through evapotranspiration of 4-5 mm. While accurate predictions for soil moisture deficit are essential for supplying water to plants through irrigation when rainfall is insufficient, soil moisture deficit is difficult to assess. In Malaysia (as in other oil palm-growing countries) rainfall and rain days are the sole climatic parameters recorded; this limited information is insufficient for reliable estimates of water deficit. This paper reports the adoption of a new method of prediction for soil moisture deficit that takes into account the effective rainfall, evapotranspiration, and a correction factor for the water-holding capacity of the soil. Monthly effective rainfall varied from 11% of gross rainfall to 84%. The number of months with soil water deficit varied from 2 to 12 (mean = 9). Values of water deficit obtained were close to those calculated using the Penman equation, thus validating this method of prediction of water deficit.

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