Application of rubber growth models and soil water balance to evaluate crop coefficient for rubber
1997
Van Rans, E. | J. Kosaiseveet | Verplancke, H. | S. Pratummintrat | S. Somnak | Shamshuddin Jusop
Many Projects have been earmarked for rubber cultivation in Northeastern Thailand although the area is regarded unsuitable. People question the viability of growing rubber in a region where rainfall is low and dry period is long. This study was assigned to use rubber growth models to evaluate crop coefficient for rubber. Four soil series along a toposequence in Maha Sarakharm Province were studied using RRlM 600 clone. The growing perriod of rubber tree was related with humidity index. The index was obtained from the crop evapo-transpiration (Etcrop) which was calculated from actual evaporation (PAN A, Etp) and crop coefficient for young rubber (Kc), Etcrop = ETp x Kc. The crop coefficient for young rubber was evaluated, using field soil moisture data based on soil water balance and law of constancy of mass. The crop coefficient value for rubber (Kc) was modified around the year with the relative soil moisture content in each soil averaging 0.71 g/cm3• The girth of rubber trees showed highly significant correlation with the land index. The growth models tested were GI =50 0.907496 + 0.145276 LI (R2 = 0.98) and TY = ---------------------------, where (0.907946 + 0.145276 LI)GI is girth increment, LI is land index and TY is tapping year. The models were used to evaluate the establishment of rubber in Ubon Ratchathanee province.
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