The R & D efforts of Rubber Research Institute of India led to development of region-specific high yielding clones, farm mechanization and new techniques for nursery, farm management and crop harvesting for enhancing cost competitiveness and addressing labour shortage. Based on these recommendations, a Benefit Cost Ratio (BCR) analysis was done to check whether natural rubber (NR) cultivation can be made sustainable under the current scenario of plunge in prices. Adopting technology-driven good agricultural practices to increase productivity and reduce cost of production in NR holdings is the key to improve the BCR and thus ensuring sustained supply of NR in the country. The BCRs of NR cultivation under different price and productivity scenarios in the traditional, North East and North Konkan regions were estimated. The present analyses show that adoption of technological innovations with cost-saving and income-enhancing measures can make NR cultivation moderately profitable even during the prevailing low price scenario. In the prevailing situation of low NR price and high labour/input costs, reducing cost of production has a greator impact on improving BCR than increasing productivity. Adopting technological innovations can still make NR harvesting from existing mature holdings profitable. Having invested in developing a rubber plantation, leaving it untapped, blaming low price and absence of any bailout schemes from the government is a lost economic opportunity for the grower and a national waste.

Soil CO2 flux, also often referred as soil respiration is defined as the emission of CO2 generated in the soil as a result of microbial and root activities. Soil CO2 flux was measured and related to soil temperature and moisture in a 21 year old rubber plantation in central Kerala for a period of two years (June, 2010 to May, 2012). Measurements were made on an hourly basis for 272 days in the first year and 308 days in the second year. Soil respiration varied between the two years as well as between seasons in a given year due to variations in soil temperature and moisture. Total amount of CO2 emitted was more in 2010-11 (26.1 tonnes ha-1) than in 2011-12 (20.7 tonnes ha-1) which was apparently related to more rainfall and number of rainy days in 2010-11 than in 2011-12. Soil respiration was slightly more in the night than in the day indicating that the cooler temperature of the night favoured more soil respiration. Soil respiration was higher during monsoon and summer seasons than during post monsoon and winter seasons in both the years. During monsoon, post monsoon, winter and summer seasons, the soil CO2 fluxes were 2.21, 1.45, 1.47 and 2.19 μmol m-2 s-1, respectively in 2010-11. In 2011-12, the soil CO2 fluxes were 1.78, 1.15, 0.98 and 1.75 μmol m-2 s-1 during monsoon, post monsoon, winter and summer seasons, respectively. In general, warmer temperatures favoured more soil respiration when sufficient moisture was available in the soil. When soil moisture status remained continuously high for longer periods, soil CO2 fluxes were impaired. Sudden and intense rainfall during an otherwise relatively dry period led to voluminous eruption of CO2 from soil as observed during many instances in winter and summer seasons in both the years. This may be due to burst of entrapped CO2 in soil pores by rain water. Availability of moisture in soil was more critical than the soil temperature for soil respiration during summer whereas during wet periods, the soil temperature was more important. Rising temperature and changes in the amount and pattern of rainfall as a consequent effect of climate change may affect soil respiration rates which can have profound impact on global carbon cycle and also on soil organic matter, a key component that determines soil fertility. 

Fourteen Hevea clones were assessed for their growth and yield performance in a large scale trial planted in 1989 in Dakshin Kannada district in Karnataka state in southern part of India. Clone RRII 203 had the highest girth after 13 years of tapping (101 cm) which was significantly higher than that of the reference clone RRII 105. Annual girth increment during the immature period was also the highest for RRII 203 (6.4 cm year-1) and this was significantly higher than that of RRII 105 (5.5 cm year-1). Analysis of bole volume of 29 year old trees revealed that RRII 203, PB 255, KRS 25 and RRII 308 were significantly superior to RRII 105. Among the clones tested, RRII 203 recorded the highest (62.9 g t-1 t-1) and significantly higher mean yield over 13 years of tapping than that of RRII 105 (44.9 g t-1 t-1). Clones PB 255 and KRS 25 also had superior growth and yield, as well as tree stand, compared to that of RRII 105. Among the tested clones, PB 255, RRII 203, KRS 25, RRII 308 and reference clone RRII 105 had yield-stability index (YSi) greater than the mean YS. Based on long term growth and yield performance, RRII 203, KRS 25 and PB 255 were selected for further on-farm evaluation prior to release for commercial cultivation. 

Leaf is a metabolically active part of any plant and its chemical composition is a good guide to the plants’ nutritional status. Leaf nutrient status of mature rubber plantations in the estate sector of South India was assessed in a uniform population for the nutrients N, P, K, Ca and Mg. Less than three per cent of the population alone expressed low values for N and P. Six per cent of the population expressed low values for K and 11.0 per cent of the population recorded low values for Mg. However, 30 per cent of the population recorded Ca values lower than the critical level indicating the necessity of supplementation of Ca along with N, P, K and Mg. Among the five nutrients studied, the coefficient of variation was high for K, Ca and Mg. Though a negative correlation was observed between P and Ca concentration with yield, the regression coefficient was too small as expected, as the yield is influenced by many factors and the tree nutritional status in totality with optimum balance among the nutrients, is influencing the yield. Significant interrelationship among the nutrients was recorded in correlation studies. 

Powdery mildew is the major fungal leaf disease of rubber in Tripura. A field trial was conducted to assess the economic impact of sulphur dusting against powdery mildew in 23 year old rubber plantations of clones RRII 105 and RRIM 600. Higher incidence and severity of powdery mildew disease was observed in RRII 105. The average severity of powdery mildew disease in sulphur dusted blocks of the two clones was 28.6 per cent as compared to 55.8 per cent in the undusted blocks. The growth of the trees was adversely affected in the undusted blocks of both the clones. The mean annual crop loss was estimated to be 19.5 and 14.2 per cent in the undusted blocks of RRII 105 and RRIM 600, respectively. The economic advantage of sulphur dusting as control measure against powdery mildew disease was evident as cost of dusting compensated by 1.22 per cent increment in the yield based on the then prevailing costs and price of rubber. 

In India, natural rubber (Hevea brasiliensis) is cultivated in around 8,27,000 hectares of arable land. Major share of the NR growing regions experiences tropical humid climate and the soils are mainly Ultisols with low base saturation, high exchangeable Al and acidic pH. Studies were conducted to monitor the growth of NR seedlings in soils having three different pH viz. 4.4, 5.5 and 7.4 with wide variations in base status in the laboratory condition and in the open-air condition in polythene bags. In the laboratory study, the length and biomass of shoot and root were monitored and in the polythene bags, growth of the plants in terms of shoot diameter, root length, shoot and root biomass at periodic interval (45, 90 and 240 days) were monitored. Growth up to 30 days in the laboratory condition was not affected by soil conditions. In the second experiment, growth measurements on the 45th day indicated no difference between plants grown in soils with three distinctly different pH. However, at 90 days and 240 days significantly lower growth was recorded by plants grown in extremely acidic pH (4.4). Highest growth was recorded by plants grown at pH 7.4. The shoot and root biomass also recorded similar trend. Growth of plants was reduced at extremely acidic pH which may be due to the combined effect of extreme acidity and high Al3+ and H+ ions and low availability of nutrients warranting soil acidity and specific nutrient management for maintaining soil productivity and good growth of rubber plants.