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Long term performance of four hybrid Hevea clones and ten ortet selections including nine from a high elevation site within the traditional rubber growing tract of Kerala was studied. Significant variability was observed among the hybrids and ortets for all major agronomic traits. Growth of rubber trees was invariably poor in the high altitude region and tappability by the tenth year of planting was less than 50 per cent. The hybrid clones RRII 203 and RRIC 100 showed highest growth vigour with 80 per cent tappability by the 13th year of planting. Among the ortets, P 270 and Iritty 1 recorded the highest tappability of 64 per cent. The ortet P 270 was the best performer with the highest girth at the opening (61 cm), girth increment during immaturity (5.5 cm) on tapping (3.4 cm) and bole volume (0.1 m3). RRII 203 was the highest yielding clone with 56 g tree-1 tap-1 over eight years of tapping. High annual yield (48 g tree-1 tap-1) and lean season yield of P 270 combined with high drc on par with the highest yielding clone RRII 203 indicated the specific adaptability of this ortet to high elevation areas. The ortets P 213 and Iritty 1 and hybrid clone RRIC 100 were the other promising clones exhibiting growth adaptation and high yield potential under high altitude conditions.

A field experiment was conducted for 2 years at the Indian Agricultural Research Institute, New Delhi to study the effects of duration of variety and nitrogen fertilization on the Ca, Mg and S concentration and uptake in rice. In general, the concentrations of Ca, Mg and S were not significantly influenced by the duration of the rice variety. N fertilization had a tendency to increase the concentration of Ca, Mg and S at 45 days after transplanting as well as at harvest; however, the difference was significant only in the case of the Ca concentration in the grain and only when the N level was raised from 60 to 120 kg N/ha. The duration of the rice variety had a significant effect on the Ca, Mg and S uptake by the straw and grain at harvest, which was higher in the medium duration variety Pusa Basmati-1 than in Pusa Jaldi Dhan-1, mainly due to the higher yields obtained with the former cultivar. Nitrogen application significantly increased the Ca, Mg and S uptake at harvest mainly due to its increasing effects on the grain and straw yields of rice. The average uptake of Ca, Mg and S was 12.6, 13.6 and 3.5 kg per metric ton of grain, respectively.

A laboratory study at the Indian Agricultural Research Institute, New Delhi showed that DCD was an efficient nitrification inhibitor under field capacity moisture ( 7 30 kPa) but not so under submerged soil conditions. Nitrification inhibition by DCD was 79.6% after 1 week of incubation and decreased to 59.3% after 3 weeks of incubation under field capacity moisture, while it was only 19.3% after 1 week of incubation and 10.6% and 18.4% after 2 and 3 weeks of incubation under submergence, respectively. DCD can play an important role in reducing N losses from agricultural fields.

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