The phosphorus status of soils of the three major rubber growing zones of Nigeria (western, eastern and  central) were evaluated.   Available phosphorus was extracted by the methods  of Bray and  Kurtz  No. 1, Bray and  Krutz No.2 and Olsen.   The various  forms of P were  also determined.   Total soil P ranged from 58.0 to 337.3 ppm with active P constituting  between 13 and 33 per cent.   Organic P ranged from 29 to 88 ppm while the standard P requirement  of the soils ranged  from 6 to 120 ppm.  The relative abundance of the various inorganic P forms was in the order  of inactive P>Fe-P>Al-P> Ca-P.

Total and organic forms of P correlated negatively with clay and positively with sand.  Available P extracted  by the three methods correlated with Fe-P, Al-P and Ca-P.  The higher correlation coefficient with Al-P and Fe-P shows that they contribute more to soil available P in  these soils.

The present trend in the rubber industry  is to increase the  test  temperature in order to reduce testing time and  increase productivity  of   the rheometer. This is claimed  to be possible with the new  rheometers viz., the Oscillating Disk Rheometer (ODR2000) and the rotorless Moving Die  Rheometer (MDR 2000) which have  been  introduced   to replace old  models like TM100. The temperature   recovery  on the ODR 2000 and MDR2000 was found  to be between  30 and 50 seconds, while it was around 6 minutes on TM100. Comparative  studies among these three rheometers   using  rubber  compounds   of  varying  cure  systems  have     been  carried   out. Comparison of the cure curves or parameters, at a particular test temperature, showed that there were  only slight differences between TM100 and ODR2000. However, there were significant differences between TM100 and MDR2000 and likewise between ODR2000 and MDR2000. At a   specified test temperature for a compound, the rheometers gave values of cure parameters viz., scorch time, cure time and cure rate in the following order: MDR2000<ODR2000<TM100. The ranking  for the delta torque values, however, is ODR2000, TM100>MDR2000. Statistical analysis on the cure parameters  of natural rubber compounds  was also carried out to examine the relationship  of the values obtained  between these rheometers.

Forty clones of Wickham origin were assessed for the extent of diversity in respect of rubber yield and various physiological, morphological and structural attributes.   Significant clonal variation was recorded for all the traits studied.  The existence of considerable genetic diversity among the clones was revealed.  Employing the Mahalanobis' D² statistic, the clones were found to belong  to eight genetically divergent  clusters.   Geographic diversity  had  no relation  with genetic  diversity.    Volume of latex, plugging index  and  dry  rubber  yield contributed  most towards  genetic divergence.

The effect of moisture stress  on growth and  latex  production of Hevea brasiliensis in Sri Lanka was  investigated and  suitable agronomic practices  to overcome the  adverse effects suggested. Among the different soil management practices, application of straw mulch resulted in higher girthing of plants, compared to other  practices  such  as growing leguminous covers  or natural vegetation.   Similarly,  tappability and  yield  were  much  higher  in mulched plots.    Mulching also contributed to soil nutrients, improved CEC and  raised  soil pH.   Mulching also improved the  potassium content and  the water  status  of both  plants and  soil.   A quadratic response to the application of K was observed.  Under conditions of moisture stress, increasing the level of  K helped in  restoring normal growth of rubber  plants.  These results were supported by observations on physiological parameters such  as stomatal conductance, transpiration and  leaf water  potential.

Resistance of natural  rubber vulcanizates  towards hot aqueous solutions  of a few industrially important chemicals was studied.  Absorption of water by rubbers containing lyophilic materials is a diffusion/osmotic phenomenon.    Retention of strength  after ageing  in distilled  water  is lower, compared  to that after ageing in aqueous media containing acid or alkali, provided  the media  are inert  towards  rubber.   As the concentration  of acid or alkali in the ageing  media increases, the tendency for water  to diffuse into the rubber  matrix gets reduced.    Reinforcing and  nonhydrophilic fillers were found  to reduce  water absorption.

Rigidoporus Iignosus, widespread  in equatorial and humid tropical zones, is the most dangerous root parasite on rubber tree. Twenty isolates collected from a wide range of geographical origins were studied  to evaluate intraspecific   variability of this fungus  using native polyacrylamide gel electrophoresis  technique.  Soluble protein banding patterns obtained by isoelectric focusing and isozyme profiles showed a high level of intraspecific polymorphism  in R. Lignosus. Factor analysis of soluble protein banding patterns unequivocally separated several groups of isolates according to their geographical origins.   Enzyme profile comparisons also conformed to biogeographical  patterns, with greatest isozyme polymorphism  in the Far-East than in Africa. However, geographical distances by themselves were not sufficient to explain all the intraspecific variability.