The extent of the drop in domestic production and price of natural rubber (NR) currently being witnessed are unparalleled in the history of NR cultivation in India.  There are no indications of the price returning to the previous high levels any time soon and contraction in the economy due to the COVID-19 lockdown has further worsened the situation. The present study critically analyses how much income an average small grower can possibly expect to get given the current low productivity and price of NR and the small size of the holdings. Operational profitability of NR harvesting in terms of the Benefit Cost Ratio (BCR) may be still attractive at the current low price, particularly in holdings with better productivity and adopting low-frequency tapping. Resorting to self-tapping by the grower will obviously further improve the BCR. However, the total revenue a small NR grower with 0.5 ha can expect today even with the best BCR is still far less than the earnings of an agricultural labourer or the average household expenditure in rural Kerala. The net income from an average NR smallholding doing alternate daily tapping is less than that of a BPL family.  Thanks to the smallholding size, today rubber is not a rich man’s crop unlike what many presume. The fact that 25-30 per cent of the holdings are presently left untapped and only a small fraction of the smallholders has resorted to self-tapping suggest that a large number of smallholders does not have a primary stake in NR cultivation any longer.  Low price of rubber is a disincentive, particularly for households that depend on NR cultivation as the main source of livelihood.  The very small size of the NR holdings is a major structural impediment to the sustainability of the Indian NR plantation sector due to their poor scale of economy.

Traditional rubber growing regions in India were historically under homestead farming where multiple enterprises co-existed catering to the diverse needs of the farm family. Introduction of natural rubber (Hevea brasiliensis Muell. Arg.) to India by British planters transformed the land use pattern considerably during the last century; a major share of home gardens was converted to monoculture rubber plantations. The history of this transformation, various intercropping practices and research carried out at Rubber Research Institute of India to conserve/increase biodiversity in rubber plantations by developing suitable intercropping systems and permitting natural flora to co-exist with rubber and the impact of crop/species diversification on soil health and resilience are summarized in this review. Conservation of soil moisture by permitting other crops and weeds in rubber plantations and subsequent mitigation of the risks associated with climate uncertainties, revenue generation in the production system and future research priorities are also discussed. Rubber intercropping systems in other South and South East Asian countries are also discussed.

Present study utilized earth observation satellite data to map acreage of existing natural rubber plantations in India to develop a geo-spatial decision support system for the NR plantation sector in the country.  Indian and foreign satellite data were used in the study.  Multi-resolution and multi-temporal satellite data were acquired according to phenology of rubber trees for delineation, mapping and estimation of the spatial extent of NR plantations.  Standard visual interpretation, satellite data classification, on-screen vectorization, extensive ground truth, survey data of NR area statistics, etc. were followed to complete the study.  Results found that satellite-derived acreage of NR plantations of age three years and above in the country was estimated to be around 7,22,440 ha. The spatial extent of NR plantations estimated was the highest in the state of Kerala (5,58,600 ha) followed by Tripura (76,954 ha), Karnataka (31,232 ha) and Assam (30,804 ha). Traditional NR growing regions contributed 77 per cent of the total NR plantations in the country, followed by North-eastern states (18%) and Konkan region (5%). Multi-spectral satellite sensors used in this study (both Indian and foreign) were found effective for mapping NR plantations’ age three years and above at different scale. Spatial distribution maps of NR were geo-spatially analysed and different useful scientific outcomes were generated.  Remote sensing based acreage of NR plantations, scientific uses of geo-referenced NR area distribution maps and necessity of updating the mapping of NR plantations in the country (using latest satellite data) are discussed. Use of geo-spatial technology for mapping entire NR plantations in the whole country was a first attempt in India and it is a powerful tool to monitor changes in the NR plantation landscape of the country in time and space.

Water mining by mature rubber trees grown under three different agro-climatic conditions, viz. traditional rubber growing region in Kerala, and two non-traditional regions, namely the hot and dry North Konkan region in Maharastra and cold Sub-Himalayan region in West Bengal was measured using thermal dissipation probes (TDP). In Kerala and West Bengal, rubber trees were grown under rain fed conditions whereas in the drought prone Maharastra, they were grown either as rain fed or irrigated (during rain-free summer months). The mean water mining rate was 22 L tree-1 day-1 in Kerala, around 23 L tree-1 day-1 in West Bengal and around 25 and 19 L tree-1day-1 for irrigated and rain fed trees, respectively in Maharastra. Water use efficiency (WUE) of mature rubber trees estimated as dry rubber production or tree biomass for a unit amount of water consumed varied between the three regions. In Kerala this worked out to be 8.0x10-4 kg rubber kg-1 water and 3.8x10-3 kg biomass kg-1 water whereas in the drought-prone Maharastra WUE was very less (3.7x10-4 kg rubber kg-1 water and 2.0x10-3 kg biomass kg-1 water in rain fed and 4.8x10-4kg rubber kg-1 water and 2.3x10-3 kg biomass kg-1 water in irrigated trees). In the case of cold prone West Bengal, WUE was 6.7x10-4 kg rubber kg-1 water and 3.4x10-3 kg biomass kg-1 water. Our results showed that the higher the rubber yield or biomass production, the higher the WUE and therefore, WUE of rubber trees is determined predominantly by rubber yield or biomass production rather than by the amount of water consumed.

Information on spatial variability of soil fertility parameters is important for efficient nutrient management and sustaining soil fertility and crop yield. The present study examined the spatial variability of plant available micronutrients Zn and B status in the traditional rubber growing regions and Konkan region of India. Geo-referenced soil samples were collected from rubber growing regions in Kerala, Kanyakumari district of Tamil Nadu, Dakshina Kannada, Udupi, Chikkamagaluru, Coorg and Shimoga districts of Karnataka, Goa and Sindhudurg district of Maharashtra during 2012 to 2013 and available Zn and B were estimated in these soils. Maps showing the spatial distribution of these nutrients in the study areas were prepared using geostatistical tools. Available Zn status varied from 0.01 to 10.91 mg kg-1 and available B from 0.01 to 2.48 mg kg-1. In Kerala, Goa and Maharashtra available Zn status was adequate in 50, 44 and 58 per cent of the rubber growing areas, respectively.  Adequate level of available Zn status was found in majority (93%) of the rubber growing areas in Kanyakumari district of Tamil Nadu whereas most (99%) of the studied areas in Karnataka was low in available Zn status.  In general, available B status was low.  The entire rubber growing areas in Goa, Maharashtra and most of the areas (99%) in Karnataka were low in available B status.  In Kanyakumari district, 66 per cent of the rubber growing area showed adequate level of available B whereas 67 per cent of the area in Kerala was low in available B status.  Wide spatial variability in both nutrients was also observed among the various districts in Kerala.  This study shows that blanket approach in micro nutrient management isnot correct and site-specific micronutrient management is to be adopted in rubber plantations in the traditional rubber growing regions and Konkan region of India for sustaining soil fertility and better resource management.

A field experiment to study the effect of integration of chemical fertilizers with bio inoculants on soil fertility and growth of natural rubber plants was conducted at two locations in the traditional rubber growing region of South India experiencing humid tropical climate. After two to three rounds of application, build­up of phosphobacteria was significant in both the locations in both recordings. Azotobacter and Pseudomonas build up was noticed in a few recordings.  Root infection of AMF was more than 90 per cent in both control and treated plants indicating natural infection in rubber roots. The inorganic nitrogen (N) in the soil, especially in the ammoniacal N form was improved by bio inoculant treatments either alone or in combination with chemical fertilizers. The beneficial effect of phosphorus (P) solubilizing microbes on P transformation was indicated through the significant difference in the P fractions, especially on Fe-P fraction.  The positive effect was more pronounced in one location where the organic carbon status of the soil was very high.  The influence of fertilizer P was directly reflected on the Ca-P fraction.  Growth of rubber plants recorded at periodical interval did not show significant difference between the treatments indicating lack of response of rubber plants to applied nutrients. Better understanding of the nutrient dynamics, having continuous uptake with roots spreading to the deeper layers of the soil and release and availability from the slowly available fractions and organic forms is required to explain the soil test crop responses in a perennial crop like natural rubber.