In the context of rising demand for natural rubber (NR) and fall in its domestic production, it is important to assess the country’s capacity to produce NR in the coming years.  Since productivity is highly dependent on the age of rubber trees, age composition of the NR holdings is a major determinant of production capacity.  By analysing the demographic trends using historic data of new/replanting in the country between 1956-57 and 2018-19, it was evident that the rate of annual replanting was highly inadequate to replace all the old holdings existing at any point of time. We adopted a scientifically precise and robust method to estimate the fraction of the older holdings getting added to the less productive senile category every year after replanting.  Share of the senile holdings consistently increased over the years.  As of 2020-21, 35 per cent of the holdings was 25 years or older (which was as high as 41% of the mature area) and this share will increase in the coming years if the present low planting tempo continued.  Given that most growers in India adopt alternate daily tapping, holdings that are 25 years or older are likely to be highly unproductive and therefore unprofitable to tap when NR price is low. 

We modelled the past and future trajectories of NR production capacity, defined as the sum of the product of mature area in different ages and the corresponding productivity.  Our analysis revealed two peaks in production capacity, one reaching a high in 2001-02 (8.7 to 9.0 lakh tonnes yr-1) and the other in 2024-25 (10.9 to 11.5 lakh tonnes yr-1). The first peak reflected the planting boom during the decade of the 1980s, catalysed by the release of the first indigenously developed high yielding hybrid rubber clone, RRII 105 and supported by proactive extension efforts by the Rubber Board.  The second peak reflected the massive planting activity for several years that was seen around the world from the middle of the decade of 2000 triggered by a steep rise in NR price.  Presently the planting rate in the country is at a historic low.  Our model predicts that NR production capacity which is presently on the rise will steadily decline in direct proportion to an increasing share of senile holdings from as early as the middle of the current decade which will be hard to reverse for several years to come even if aggressive re/new planting is done now; thanks to the long gestation period of the crop. 

Our model forecasts that NR deficit is likely to increase drastically, warranting more imports in the coming years which will be incongruous with the vision envisaged in the National Rubber Policy and may not be the best desirable option for the NR consuming industry in India. Alternatively, and more likely, the industry may increase the share of consumption of synthetic rubbers which is not in the best interest of the NR grower community or environmental sustainability.  Yet another eventuality might be migration of the industry to those countries that produce surplus quantities of NR, but this will be contradictory to the spirit of Aatma Nirbhar Bharat Abhiyaan. 

Status and distribution of total and different fractions of zinc (Zn) in the nine major series of the rubber growing soils of South India was assessed.  Total Zn status of the soil was comparatively low and the values for the Ap horizon ranged from 47.9 to 81.7 µg g-1. Major share of the total Zn was in the residual fraction which ranged from 25.9 to 70.8 µg g-1 in the Ap horizon among the series.  The water soluble plus exchangeable fraction of Zn for the Ap horizon ranged from 0.19 to 1.83 µg g-1 among the series and the values reduced down the horizons. Among the nine series, the plant available fraction of Zn was found to be extremely low in Kanjirappally, Thiruvanchoor and Lahai series.  Low status of total Zn indicates chances of depletion of Zn reserve with repeated cycles of cultivation.  Replenishment of Zn through fertilizer to these soils especially to Kanjirappally, Thiruvanchoor and Lahai series may be beneficial for improving the plant growth and maintaining/sustaining the Zn status of the soil.

Tapping Panel Dryness (TPD) is a physiological disorder having a negative impact on crop productivity in rubber cultivations.  Factors such as clones, tapping systems, climatic conditions, use of yield stimulants etc. are some attributes considered to be related to TPD in commercial rubber plantations. In this study the propensity of a few widely planted rubber clones to TPD under two different agro-ecological regions and different stages of the tapping cycle was investigated.  The regression model for the relationship between years of tapping and mean percentage incidence of TPD done separately for all estates revealed a positive trend with significant regression coefficients. The increase in mean percentage incidence of TPD for each year of tapping was relatively high in the WL1a agro-ecological region and even among the three estates in the WL 1a agro-ecological region it was highest in the estate recording the highest annual rainfall and wet days. The propensity of a rubber tree becoming dry was found to be almost double in panel BO-2 than in panel BO-1. Clones RRIC 121, RRIC 130, RRISL 201 and RRISL 217 showed differences with regard to increase in mean percentage incidence of TPD per year of tapping during the first five years of tapping. Judicious use of yield stimulants would not enhance the percentage incidence of TPD as per the findings of this study.  The possible loss in crop productivity during the early stages of the tapping cycle for some of the newly recommended clones due to TPD, in Sri Lanka was estimated.

As a perennial tree crop, maintaining identity of different clones of Hevea brasiliensis is important in crop management system and research. Characterisation of RRII 400 series clones derived from same parental combinations for distinguishable phenotypic variations were very low and overlapping especially in the nursery stage. In this context, a set of distal pulvinus anatomical traits viz. shape of the vascular bundles in the abaxial and adaxial side, inter-vascular continuity, medullary bundles, intrusion of cortical cells into the pith, shape of pith etc. were used for identification of  six Hevea clones viz. RRII 414, RRII 417, RRII 422, RRII 430, RRII 105 and RRIC 100. Among these, shape of vascular bundles, features of inter-vascular continuity and intrusion of cortical cells, proportion of vasculature and pith area in the stele are observed to be stable anatomical markers for identification of the above clones.  RRII 414 showed a close affinity to the female parent RRII 105 and RRII 430 showed more resemblance to its male parent RRIC 100.  The other two clones viz. RRII 417 and RRII 422 are intermediate with respect to these traits. Structural traits showed more resemblance between RRII 414 and RRII 422.  Among the six clones studied, RRII 430 showed both morphological and anatomical identity with RRIC 100. It is obvious that anatomical characteristics represent the environmental adaptation of clones and hence could be used as reasonably reliable adjuncts for identification of Hevea clones. 

The present study was taken up to compare yield response of continuous Low Frequency Controlled Upward Tapping (LFCUT) from old and senile rubber trees of clone RRII 118 at Central Experiment Station of Rubber Research Institute of India. The trial was conducted for six years in the virgin bark of high panel above the renewed panels.  Mean dry rubber yield over six years period under S/4 d3 frequency was comparable to S/4 d4, S/3 d4 and S/3 d7 frequencies of tapping. An increase in yield of 23 and 52 per cent was observed in the first year of high panel tapping under S/3 d4 with once in six week stimulation and S/3 d7 with once in three weeks stimulation over S/4 d3 with once in six weeks stimulation.  However, considering the overall mean for six years, yield increase of 26 per cent could be obtained under S/3 d7 with once in three weeks stimulation than S/4 d3 with once in six weeks stimulation.  By adopting d4 and d7 frequencies of tapping, requirement of tapper can be reduced by 25 and 51 per cent, respectively, compared to third daily tapping (d3), with the additional benefits of long term sustainable yield and longer economic life at reduced cost. Practice of continuous controlled upward tapping (CUT) is ideal for assured sustainable rubber production even from trees having unsuitable renewed basal panel, due to high incidence of tapping panel dryness (TPD). 

Variations in soil organic carbon (OC) content and stock in the rubber growing soils in different states in South India were studied.  Soil samples were collected from the traditionally rubber grown areas in Kerala and Tamil Nadu and also from recently cultivated areas in Karnataka, Goa and Maharashtra states.  One composite sample (0-30 cm) of three sub samples from each unit of 50 ha rubber area were collected.  Soil core samples also were taken to estimate the coarse fraction (gravel > 2 mm).  Soil OC estimations and the volume and weight of gravel and fine earth (< 2mm) were determined following standard protocols.  Based on the OC content (%) and weight of the fine earth portion, the stock OC present in the 0-30 cm soil layer was estimated on tonnes ha-1 basis and the samples from each district / state were categorized to low, medium, high and very high classes.  It was observed that more than 90 per cent of the soil samples from rubber grown areas in all the districts / states belonged to the medium, high or very high status.  Considerable variations were noticed in the percentage distribution of samples among the high and very high classes based on OC content and OC stock. However, as observed in the case of OC content, more than 90 per cent of the soil samples were adequate in stock OC also in all the districts / states, except in Thiruvananthapuram and Palakkad districts.  The OC stock in rubber growing soils in South India ranged from 36.5 to 61.4 tonnes ha-1.