Geo-informatics Techniques for Assessing Physiological Status and Productivity of RRIC 121 Genotype of Hevea brasiliensis (Rubber) under Different Harvesting Systems

AbstractRubber (Hevea brasiliensis) one of the main plantation crops in Sri Lanka is the onlyplant species cultivated commercially for natural rubber harvesting. Novel systems forharvesting have been introduced but spatial distribution of photosynthetic potentialdetermining key factor for sustainable cultivation has not been properly explored. Use of suchtechniques such as Satellite Remote Sensing (RS) and Geographic Information System (GIS)to analyse spatial and biological factors related to the productivity of rubber plantation withdifferent harvesting systems is the main objective of the present study.Quikebird high resolution satellite images were used for RS analysis. Chlorophyllcontent of rubber leaves was measured using a SPAD-502 chlorophyll meter. Chlorophyllcontent and satellite images were analysed using GIS and spatial statistical methods todetermine the variation in different harvesting systems. Yield data were collected from thestudy site and yield parameters were correlated with chlorophyll content and NormalizedDifference Vegetation Index (NDVI) values. Results revealed all systems exhibitedpromising yield performance without significant deviation but slightly higher yield perhectare per year (YPH) and dry rubber content of latex (DRC) were recorded in quarter spiralbased once in three days (S/3 d4) and weekly (S/2 d1 2d7) harvesting systems. Chlorophyllcontent and rubber yield showed direct correlation in all systems. NDVI vs chlorophyllshowed positive correlation r2=0.65 and spatial distribution of chlorophyll and NDVI valuesdemonstrated sound physiological status of plants across the plantation with differentharvesting systems. Cost effective LIH systems showed better production trenddemonstrating relatively higher yield while reducing tapping cost and labour. Satellite basedremote sensing technique is an easy and efficient tool to estimate productivity of rubberplantation over a large area.Keywords: Chlorophyll, NDVI, harvesting, Remote Sensing, Rubber

RESPONSE OF LOW FREQUENCY HARVESTING SYSTEMS OF RUBBER UNDER DRIER CLIMATIC CONDITIONS IN SRI LANKA

Escalating cost of production (COP) and inadequate supply of skilled harvesters are among the major issuesthat natural rubber industry face today. Low frequency harvesting (LFH) systems of which trees are tappedin a lesser frequency than once in two days, are considered to be one of the solutions to overcome theseissues. With the focus given to expand rubber in drier climates, the present study was aimed to investigateon the yield response of LFH systems, viz. harvesting trees once in three (d3), four (d4) and six (d6) days inthe intermediate zone (IZ) with the stimulation protocols developed for the wet zone (WZ). With thedecrease in harvesting frequency in IZ, yield per tree per tapping (GTT) increased, however yield per treeper year (YPT) decreased. No such declines were observed in WZ. Stimulation had no negative impact onpercentage dry rubber content in latex (%DRC) or incidence of Tapping Panel Dryness. Whilst only the S/2d3 system is acceptable for IZ in the present form, stimulation protocols are to be revised in other LFHsystems. Bark consumption was reduced significantly by LFH resulting in several long-term beneficialeffects. Effect of stimulation on latex physiology is also discussed.Keywords: Climate change, Ethephon, Hevea, Low frequency harvesting, Rubbe

Profitability of Adopting Extended Low Intensity Harvesting Systems for Rubber

In harvesting, rubber tree is generally tapped along the half of the circumference of the trunkwith the frequency of once in two days (S/2 d2). Low intensity harvesting (LIH) systems inrubber plantations appeared to be a practical solution to address the issues related to labour,high rate of bark consumption and cost of production. Low intensity of harvesting could beachieved by reducing either the frequency of harvesting or tapping cut length or both.Recently two extended low intensity systems i.e. S/2 d4 (tapped along the half of thecircumference of the trunk with once in four days frequency) and S/4 d3 (tapped along thequarter of the circumference of the trunk with once in three days frequency) wasrecommended for harvesting rubber in Sri Lanka. Generally no estate would adopt LIHsystems in its full extent. Therefore, profitability of adopting S/2 d4 and S/4 d3 systems in anestate with 500 ha at different rates was worked out for general information. In this case,effects on production cost, net income and harvester requirement were analysed withdifferent adoption rates.Adoption of S/2 d4 and S/4 d3 systems may reduce the total production cost at rates of 1.86and 1.73 million rupees per 10% increase in adoption extent with S/2 d4 and S/3 d4 system,respectively However, adoption of the total extent of a 500 ha estate will get the benefit ofreduction of the production cost in Rs.18.69 and 17.28 million annually compared to tappingthe total extent with S/2 d2 system.Net annual income gained from 500 ha of rubber harvested with S/2 d2 system will be Rs.95.57 Mn. Adoption in 10% of the extent with S/2 d4 and S/4 d3 harvesting systems mayincrease the net income of the estate in Rs.1.87 Mn and 1.73 Mn per year, respectively.Adoption of 100% of the area with S/2 d4 and S/4 d3 system may increase the annual netincome to Rs. 114.26 Mn and Rs. 112.85 Mn, respectively.Harvesting 500ha of mature extent with 400 tappable trees needs 333 harvesters per day at d2frequency. Adoption of 10% of the extent with d4 and d3 frequency may reduce the harvesterrequirement in 5% and 3%, respectively. However, adoption of 100% of this extent with S/2d4 and S/4 d3 harvesting systems reduces the daily required number of harvesters to 167 and222, respectively.

Preliminary Investigations of an Oil Based Ethephon Mixture (Motex Plus) on Low Intensity Harvesting Systems of Rubber

Low intensity harvesting (LIH) systems facilitate to reduce the cost of production (COP)through the reduction in the cost of tapping and also to minimise the harvester requirement inrubber plantations. In addition, considerable financial benefits are expected due to theincrease in economic lifespan of trees caused by the reduction in bark consumption. Tocompensate the yield loss due to lowering the intensity, 2-Chloroethylphosponic acid(ethephon) is used as a yield stimulant in LIH to enhance the yield per tapping. Allcommercial formulations of ethephon available in Sri Lanka have been water based.Although such formulations have an advantage in preparing different dilutions by mixingwith water, their long term effectiveness in field application are often questionable. A new oilbased formulation (Motex plus) has been introduced to Sri Lanka and therefore, the studyrecorded here was focused to assess its effectiveness in application of LIH.Performance of three low intensity systems recommended in Sri Lanka i.e. S/2 d3 (half spiralbased once in three days harvesting), S/2 d4 (half spiral based once in four days harvesting),and S/4 d3 (quarter spiral based once in three days harvesting) was tested with application of2.5% Motex Plus, every two months interval except during wintering, monthly and every twoweeks intervals, respectively together with S/2 d2 (half spiral based once in two daysharvesting) system for comparison. Dry rubber content of latex in LIH systems were above35% whilst it was about 33% in S/2 d2 system. Yield per tree per year in S/2 d3, S/2 d4 andS/4 d3 systems were 5.69 kg, 5.48 kg and 6.19 kg, respectively showing a slight higher yieldover the S/2 d2 system. Therefore potential reduction in the dose of oil based formulation isalso discussed. Number of trees affected with tapping panel dryness was comparably lower inLIH systems. Although the bark consumption per tapping was slightly higher in LIH systems,overall bark consumption has dramatically been reduced due to lesser number of tappingdays.

Effect of Some Leaf Characteristics on Determination of Leaf Chlorophyll Content of Hevea brasiliensis with SPAD-502 Chlorophyll Meter

Chlorophyll meter SPAD-502 is widely used in determining leaf chlorophyll content in fieldplants as it is non-destructive and less time consuming. Currently, there are about 25 Heveagenotypes recommended by the Rubber Research Institute of Sri Lanka. Characteristics ofleaves, i.e., leaf thickness, wax and water content varies among the genotypes and also couldaffect the readings of the SPAD-502 chlorophyll meter. Therefore, this study was carried outto investigate effect of leaf thickness, wax and water content on determination of leafchlorophyll content of H. brasiliensis with SPAD-502 chlorophyll meter.Most commonly grown Hevea genotypes i.e., RRIC 121, RRIC 100, RRISL 203 and RRISL2001 were selected for the study. Leaf samples of each genotype were collected from thebudwood nurseries in Dartonfield Estate, Agalawatta. SPAD value of each leaf sample wasmeasured and subjected to analyse the actual chlorophyll content by acetone extractionmethod. Leaf thickness, water content and epicuticular wax content of each leaf sample werealso measured by using standard test methods.The highest leaf thickness, wax content and water content were observed in RRIC 100genotype whilst RRISL 203 genotype gave the lowest values. Leaf chlorophyll content ofRRIC 121 genotype was comparatively lower with an average value of 36.51 μg/cm2.However, the highest leaf chlorophyll content was observed in RRISL 203 genotype and theaverage value was 54.28 μg/cm2. Despite the genotype average, leaf wax content and watercontent were 79.75 μg/cm2 and 55.79%, respectively whilst leaf thickness was 0.126 mm.Pearson correlation coefficients for leaf thickness, wax content and water content vs. readingof SPAD-502 chlorophyll meter were above 0.05% and revealed that these three parametersdid not affect the reading of SPAD-502 chlorophyll meter significantly (p=0.05) indetermination of leaf chlorophyll content of H. brasiliensis.Keywords: Chlorophyll, Epicuticular wax, Hevea, Leaf thicknes

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

Rubber cultivation in Eastern Province, is predominantly in the intermediate zone of whichclimatic conditions are considered to be sub-optimal for growing rubber. Due to low level ofatmospheric RH%, latex flow tends to cease early after tapping in these areas. Turgidity oflatex vessels associated with the water content of latex vessels decreases with the sunrisewhen evapotranspiration increases. Hence, time of commencing tapping greatly influences onthe latex yield. Therefore, the present study was aimed to identify the best time of the day forlatex harvesting through an assessment on latex physiological parameters. In order to identify the best time for tapping, variations in several physiological parameterstogether 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 rubbercontent (DRC%), initial flow rate (IFR) and plugging index (PI) were analysed along with theenvironmental factors at the time of tapping. Latex volume per day (LVPD) was highly associated with the overall latex yield hence hadbecome the prime factor concerned. The highest LVPD was recorded between 05:00 to 06:00hrs. Dry rubber content of latex had increased after 06:00 h and that could be attributed to thewater status of the trees which was governed by evapotranspiration. During 05:00-06:00 hrstime period, RH% was almost 100% and temperature was around 23° C. When tappingcommenced after 06:00 h, the overall yield declined. There was a tendency of increasing theplugging index (PI) with the delay of tapping. Therefore, the study concluded that high yieldscould 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 tim