Estimation of water use of mature coconut (Cocos nucifera L.) cultivars (CRIC 60 and CRIC 65) grown in the low country intermediate zone using the compensation heat pulse method (CHPM)

The compensation heat pulse method (CHPM) was used to determine the diurnal variation and daily total water use of two coconut varieties (i.e. CRIC 60 and CRIC 65) growing on two contrasting land suitability classes (i.e. S2, Kurunegala series, and S4, Kuliyapitiya series) in the low-country intermediate zone (IL1) of Sri Lanka. The average daily total sap flow (Fd) of CRIC 60 and CRIC 65 on S2 were 120 and 90 L d-1 while on S4 it was 92 and 79 L d-1 respectively. Palms on S2 showed higher Fd than those growing on S4, with 27% and 15% increases in CRIC 60 and CRIC 65 respectively. The greater soil depth and the water holding capacity of S2 and the consequently greater trunk water storage of palms growing on S2 were the probable causes. CRIC 60 showed 24% and 22% greater Fd than CRIC 65 on S2 and S4 respectively. On S4, this was primarily because of the higher leaf area per palm of CRIC 60. On S2, both varieties had similar leaf area, indicating that varietal differences in root water absorption and stem water conductance capacities were probably causing the varietal difference in Fd. On the majority of measurement days, all palms reached their maximum hourly sap flux (Fm) after 1000 h, maintained it until 1600 h followed by a rapid decline. Fd showed a strong positive correlation with Fm. A significant positive correlation between daily total sap flow and total leaf area per palm provided strong validation to the results obtained.

Keywords: Cocos nucifera L., compensation heat pulse method, daily total sap flow, maximum hourly sap flux, sap wood area.

doi :10.4038/jnsfsr.v37i3.1211

J.Natn.Sci.Foundation Sri Lanka 2009 37 (3):175-186