Evaluation of growth of eleven clones of Hevea brasiliensis in the Dooars region of West Bengal revealed that though the initial survival was high (100%) for the clone RRII 105, the growth of the clones varied significantly from the second year and by the end of the eighth year RRII 208 recorded the highest mean girth (46.53 cm) followed by RRIM 600 (46.50 cm). The mean girth increment over 8 years was also higher for the clone RRII 208. Although the overall percentage of tappable trees at the end of 7 years was only 40, RRIM 700 recorded the highest (67%) tappability followed by RRII 208 (64%). By the eighth year, overall tappability increased to 66 per cent indicating one year delay in attaining tappable girth in comparison to the trees in the traditional rubber growing region of India. On the basis of growth index the clone RRIM 600, RRII 208, RRII 105, PB 235 and SCATC 93/114 were identified as better adapted clones under the sub-tropical and sub-humid climatic conditions of Dooars region. 

Quantum yield and yield stability of eighteen clones of Hevea brasiliensis were studied under the high altitude conditions, in two clone evaluation trials comprising of ten clones each, with two clones in common. In one of the trials, low coefficients of variation and high means were observed for RRIM 600 and RRII 203 where as high coefficients of variation and high means for RRII 105 and PB 235. The highest expected average annual yield was computed for RRIM 600 followed by RRII 105. In the other trial, low coefficients of variation and high means were observed for RRII 209 and PB 311 and high coefficient of variation and high mean for RRII 105 and PB 310. However, the highest expected average annual yield was for PB 311. Successive recordings of average annual yield of clones from both trials have shown an increasing trend suggesting that it would take a few more years for yield stabilization. 

Eleven clones of Hevea brasiliensis were evaluated in a large-scale field trial at Keeriparai in the Thovalai Taluk of Kanyakumari District in India. The clones showed significant variations in casualty due to sun-scorch, juvenile girth, early tappability, girth at opening, mean girth increment over five juvenile years, bark thickness, number of latex vessel rows and test tap yield. The clones showed high variability for sun scorch casualty. This trait was also negatively correlated with growth attributes and test tap yield recorded after the incidence of sun scorch. The clones IRCA 111 and PB 314 were found suitable for the area with respect to establishment, growth, early tappability and initial yield. PB 255 and IRCA 230 were also promising clones in terms of establishment, growth and bark characters. No incidence of pink disease was observed in this trial. The control clone RRII 105 was ranked low for most of the characters evaluated. 

The suitability of interrow spacing wider than the standard 8.1 m for rubber in rubber / cinnamon intercropping was investigated. Eleven spacings ranging from 7.2 to 18.0 m were tested. The experimental design used was convenient and reduced the land requirement. Closure of rubber canopies in the 7.2 m and 8.4 m spacings by the sixth year limited the available light to 12 per cent even in the middle of the interrow. When the interrow spacing was 12 m or more, the middle of the interrow had more than 80 per cent light. The length density of fine roots of rubber (RLD) was high close to rubber trees and in treatments with narrow interrow spacings, whereas it significantly decreased with the increase in distance from rubber trees. Bark yield of cinnamon was highest in the first harvest compared to the next two. Reduction in yield in subsequent harvests was observed in treatments with narrow interrows. The yield in the third harvest was about 19 per cent of the first harvest in the 7.2 m interrow spacing. The cumulative bark yield for the three harvests increased with the increase of the interrow space. The interrow spacings of 12 m or more was found suitable for a sustainable rubber / cinnamon intercropping. Growth of rubber was not affected signifi­cantly by the spacing treatments. 

Dirt content is one of the important quality parameters specified in the grading of technically specified rubber (TSR). It is estimated by dissolving rubber in a solvent with the aid of a peptizer, such as copper oleate and then determining the weight of dry matter retained on a standard sieve, when the solution is filtered. The performance of copper soap of mixed fatty acids, prepared from rubber seed oil, was evaluated for the estimation of dirt content of TSR in comparison with that of copper oleate. The results indicated that mixed fatty acid soaps of copper prepared from rubber seed oil is as good as copper oleate for the purpose and is a cheaper alternative. 

Field and laboratory experiments were conducted in a sandy clay loam soil under rubber (Hevea brasiliensis) cultiva­tion to study the movement of surface-applied K. The field experiment indicated that the influence of K fertilizer on K availability is reflected only in the 0-10 cm layer of the soil. Higher levels of K application did not influence the available K status. In the laboratory experiment using soil columns, movement of K up to 30 cm depth was observed.