Pot culture  and  field experiments were carried out to study  the tolerance of sprouted  seeds of Hevea brasiliensis  to preplant  application  of diuron  at  the  rate of 2.5 kg/ha.   Results of the pot culture study, where planting was carried out the same day  and 1, 3, 5 or 7 days after spraying indicated no toxic effect on seedling growth.  On the contrary, a slight stimulatory effect of diuron  on seedling  growth  was noticed.   Field experiments revealed  that  growth of rubber was not adversely affected when  planted  at different intervals (same day, 1, 2, 3, 4, 5, 7 or 10 days) after spraying  diuron.

Changes in molecular level network structure have been investigated for natural  rubber (NR) cured  by low sulphur  (EV) and  urethane  (Novor^(R) systems by measurement  of continuous and  intermittent  stress relaxation. NR cured by urethane system,  showed  more crosslinking and scission reactions at temperatures between 100 and 130⁰C but lower crosslinking and scission reactions at temperatures between 150 and 160°c compared to NR cured by low sulphur system. At temperatures  between 100 and 130°C, NR vulcanized by low sulphur  system showed lower permanent set and at temperatures between 150 and 160°C higher permanent set, as compared to NR vulcanized  by urethane system. The ageing of urethane cured natural rubber, perhaps results in the occurrence of intermolecular  interactions such as hydrogen  bonding.  A lower value of activation  energy of stress  relaxation shown  by urethane  cured  NR, indicates  that the mechanism of degradation is not  identical to that of low  sulphur  cured  NR. 

A field experiment on mature rubber was conducted, continuously for five years, to study the influence of K on volume of latex and dry rubber yield in a laterite soil (red ferruginous soil) of Kerala, India.   Latex volume and dry rubber yield were significantly influenced only during  the fourth and  fifth year of treatment.   Significant yield increase was observed  only during  the summer  months indicating  the beneficial influence of K in improving  the water balance in the plant system.  The highest dry rubber yield was recorded due to the application of 75 kg K₂O/ha in the fifth year of study.    The optimum  dose of K fertilizer and  critical values of soil available K (both Morgan K and ammonium acetate K) and critical leaf K concentration were  also derived  from  the respective response model  studies.

Six oriental  Hevea clones of Indian  (RRII 208), Malaysian  (RRIM 600), Indonesian  (PR 107) and Chinese (SCATC88-13,SCATC93-114,Haiken1) origin were investigated for their performance under  two yielding regimes (Regime I = April to September; Regime II = October to January). Regression analysis  revealed  SCATC 93-114, PR 107 and  RRII 208 with  the least regression coefficients to be the stable clones and Haiken 1 to be least consistent over the regimes.  Though SCATC93-114 and  PR 107 showed  a lower regression coefficient, their respective mean yield was low making them less desirable for the tested environment. Comparatively higher contribution was  rendered   by  RRII 208 with  a low  yield  depression  (43.8%) during  Regime I ensuring higher  returns  from  the stand.    Clones SCATC 88-13 and  Haiken  1, though  not  consistent in yield  over  the  regimes, were  on  par  with  RRIM 600 with  respect  to annual  mean  yield. This study  identified  three  clones, RRII 208, SCATC 88-13 and  Haiken  1 as potential  ones for  on-farm  evaluation  in  Tripura.

The effect of continuous cultivation of rubber on soil properties  was investigated.   Soil morphological properties, organic C and total N, P and K were estimated  in the soil profiles samples  in plantations  in which  rubber was grown  for more than sixty years.   Soil samples from adjoining natural  forests were studied  for comparison.   The study revealed  that while the morphological properties were not significantly affected, the total N and K status decreased and  the P status  increased  under  continuous  rubber cultivation.   The study  points  out  that application of higher  dose  of N and  K fertilizers  and  a  reduction  of the  current  rate of P fertilizer  are  necessary.

A cropping system experiment including diverse annual and perennial intercrops with rubber was started  at  the Central Experiment Station of the Rubber Research Institute  of India  in 1993. Rubber was planted in paired rows 9.0 m apart.   The distance within the paired rows was 5.1 m.    Banana, pineapple,  black pepper  and  cocoa were planted  in the  wider  inter row spaces and legume ground cover Pueraria phaseoloides was established in the narrow inter­ row spaces.  Teak and fodder grass were grown along the boundaries.  An increase in organic matter and available phosphorus and a decline in available potassium content in the soil was noticed after 30 months.   Growth of rubber was significantly superior  in the present system compared  to that  in monoculture.  Nutrient budget  of the system indicated  a net gain of all the nutrients studied.   Benefit-cost ratio of banana, pineapple and fodder grass were 2.58,2.26 and 2.07 respectively, indicating the economic feasibility of growing banana and pineapple as intercrops and fodder grass along the boundaries during the initial three years. An evaluation of the system also indicated sustainability in terms of soil fertility maintenance.