Time Course Variation of Some Latex Physiological Parameters Associated with Yield of Rubber (Hevea brasiliensis) Grown in Eastern Province of Sri Lanka

Abstract

Rubber cultivation in Eastern Province, is predominantly in the intermediate zone of which

climatic conditions are considered to be sub-optimal for growing rubber. Due to low level of

atmospheric RH%, latex flow tends to cease early after tapping in these areas. Turgidity of

latex vessels associated with the water content of latex vessels decreases with the sunrise

when evapotranspiration increases. Hence, time of commencing tapping greatly influences on

the latex yield. Therefore, the present study was aimed to identify the best time of the day for

latex harvesting through an assessment on latex physiological parameters.

In order to identify the best time for tapping, variations in several physiological parameters

together with latex yield were assessed at different time intervals, i.e., 04:00, 05:00, 06:00,

07:00 and 08:00 in two smallholder sites in the eastern Province. Latex volume, dry rubber

content (DRC%), initial flow rate (IFR) and plugging index (PI) were analysed along with the

environmental factors at the time of tapping.

Latex volume per day (LVPD) was highly associated with the overall latex yield hence had

become the prime factor concerned. The highest LVPD was recorded between 05:00 to 06:00

hrs. Dry rubber content of latex had increased after 06:00 h and that could be attributed to the

water status of the trees which was governed by evapotranspiration. During 05:00-06:00 hrs

time period, RH% was almost 100% and temperature was around 23° C. When tapping

commenced after 06:00 h, the overall yield declined. There was a tendency of increasing the

plugging index (PI) with the delay of tapping. Therefore, the study concluded that high yields

could be obtained in this agro-ecological region if tapping is performed before 06:00 h.

Keywords: Hevea, Intermediate zone, Rubber, Sub-optimal climatic conditions, Tapping time