Influence of high background radiation on coconut nutrition

Abstract

An investigation on the influence of high background radiation on coconut palms was conducted during 1994-97 at the College of Horticulture, Vellanikkara. This study was carried out in the high background radiation areas of the coastal Kollam district. A pot culture experiment was also conducted at the College of Horticulture, Vellanikkara. Soil collected from the high background radiation area (Chavara) was used for the study. The radiation exposure of coconut roots and its influence on the root activity of coconut palms, radiation profile of coconut rhizosphere, radionuclide accumulation by coconut palms and the influence of organic matter application on absorption of radionuclides by coconut palms were assessed. The main findings are given below. A wide variation in natural background radiation ranging from 200-8 200 nGy h-1 was observed in Chavara and adjoining areas. The radiation levels were generally higher in the coastal areas compared to the inland. 232 Th was the major radionuclide contributing to the high radiation and its content in soil ranged from 144 to 3580 ppm. The results from root exposure studies indicated that plant roots are continuously exposed to high radiation levels and a significant reduction in radiation exposure occurred only at a depth of 1 m. Correlation and regression analyses revealed a significant positive relation between surface radiation and the radiation exposure at different soil depths. The root activity studies employing 32P soil injection technique revealed that the root activity of coconut palms in the high radiation areas was comparable with that in the low radiation areas.

The studies on 232Th uptake and its distribution within coconut palm pointed out that considerable accumulation of the absorbed 232Th occurs in roots and that only a small fraction of it is translocated up to the leaves and nuts. Application of organic matter, especially green leaf manure was found to be highly effective in reducing the 232Th uptake by coconut seedlings growing in monazite rich soil.