Water balance study for some rubber soils in East Thailand
1998
Pratummintra, S. | Shamshuddin Jusop | Siti Zauyah Darus | Ramst. E. Van | Verplancke, H.
Traditionally, rubber grows under rainfed conditions, except in nurseries where irrigation is necessary. Ideally the monthly rainfall should be sufficient to meet the water requirement of the rubber tree. In a tropical monsoon climate, the potential evapotranspiration rate is around 4 mm day E-1. Therefore, a monthly rainfall of 125 mm is considered essential to maintain optimum gaseous exchange. Water consumption through water balances study is based mainly on meteorological data or on the static concept, assuming no water movement between the rooting zone and the deeper soil horizons. The objective of this study was to determine the actual water use by rubber trees and to quantify the parameters in the water balance equation for crop coefficient of rubber in Thailand. In this study, rubber plantations were selected in flat areas, with average slopes of less than 2 %. Ring samples were collected from each plantation at the dept of 10, 20, 40, 60, 80, 110, 150 and 180 cm or until a consolidated layer or ground water table. The reference crop evapotranspiration (Eto) calculated by the Applied Penman Method (Frere and Popov) was found to be close to the value obtained by the PAN A method. The evapotranspiration rate in East Thailand averages around 4.94 mm/day. The crop coefficient for rubber (Kc) averages around 1.28 in all sites of study. The Kc value varies during the year, with the highest value during the rainy season (3.67 in July-August) and the lowest values found during the cold and dry season (0.14 in January-February).
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