Kr. Vijayakumar et al., IRRIGATION REQUIREMENT OF RUBBER TREES (HEVEA-BRASILIENSIS) IN THE SUBHUMID TROPICS, Agricultural water management, 35(3), 1998, pp. 245-259
North Konkan region in the west coast of India is only marginally suit
able for rubber (Hevea brasiliensis) cultivation due to subhumid clima
te. The region has a rainless period with severe soil moisture deficit
s in summer. Heavy leaf injury and shedding is experienced in summer m
onths. The immaturity period of the crop, attainment of 50 cm girth by
main trunk, in the region under rainfed conditions is very long exten
ding to more than 10 yrs. An irrigation experiment was laid out to qua
ntify the requirement of irrigation water and for comparative evaluati
on of basin and drip irrigation systems. In the experimental site, the
drip irrigation was inferior to basin irrigation. Growth rates achiev
ed under irrigation regimes of 1.00 crop evapotranspiration (ETc) and
0.50 ETc were comparable suggesting that only 50% of the estimated cro
p water requirement for the summer season is the irrigation requiremen
t. The immaturity period could be reduced to 6 yrs by irrigation. Suff
icient irrigation was found to eliminate foliar injury and to result i
n a high photosynthetic rate. Path coefficient analysis revealed that
photosynthetic rate, leaf area index, turgor pressure and leaf tempera
ture have direct and positive relationship with the fortnightly relati
ve growth rate. The results of path coefficient analysis of photosynth
etic rate with physiological factors revealed that latex solute potent
ial is the major parameter affecting the photosynthetic rate under str
ess conditions. Other parameters namely, leaf epicuticular wax, turgor
pressure, stomatal resistance and chlorophyll indirectly affect photo
synthesis. (C) 1998 Elsevier Science B.V.