Abstract
Rubber cultivation is being expanded extensively into non traditional rubber growing areas such as Moneragala district in the intermediate zone of Sri Lanka. This study determines the nutritional status of these soils for the growth of rubber [Hevea brasiliensis (A. Juss.) Muell. Arg.] and the degree of nutrient variability. Soil samples were collected from the surface layers (0 - 0.3 m) and the availability of N, P, K, and Mg status and the urease activity were determined. Leaf N, P, K, and Mg status in samples collected from Kalutara, Kegalle and Moneragala regions, were also determined to compare the nutritional status of the plants among regions. Soils in the Moneragala region exhibited a very high variability with regard to exchangeable K (23 - 273 ppm) and exchangeable Mg (15 - 346 ppm) contents. The urease activity of the soils was very low (7 μg of NH<sub>4</sub><sup>+</sup>-N released g<sup>-1 </sup>hr<sup>-1</sup>) compared to traditional rubber growing areas. This highlights the need to evaluate the agronomic effectiveness of urea as the N fertilizer in rubber growing soils in this region. Leaf N levels in the Moneragala region was significantly low but leaf Mg levels in all regions were in the high range. The fertilizer requirement of rubber plants could be highly site-specific in this region and therefore the currently used low K fertilizer mixture with a Mg source may not be equally effective in all parts of the region. <strong>Key words</strong>: intermediate zone; Moneragala; nutrients; rubber growing soils; urease activity DOI: 10.4038/jrrisl.v87i0.1811 <em>Journal of the Rubber Research Institute of Sri Lanka, </em>(2005) <strong>87</strong>, 23-35
Highlights
Rubber cultivation is being promoted in non traditional areas in the intermediate zone of Sri Lanka (e.g. Moneragala district) to increase the rubber production in Sri Lanka, to increase the forest cover in the region and to improve the social status of the poor in these areas
It is known that rubber plant can be grown in the intermediate zone of the Moneragala district, various aspects on efficient resource management to obtain the maximum economic benefits is yet to be studied in detail
Deep placement of urea in these soils is essential to increase the fertilizer use efficiency of urea, as practiced in the traditional rubber growing areas. These findings indicate the need to evaluate the agronomic effectiveness as well as the environmental concerns of different N fertilizers when used in rubber growing soils in the Moneragala District
Summary
Rubber cultivation is being promoted in non traditional areas in the intermediate zone of Sri Lanka (e.g. Moneragala district) to increase the rubber production in Sri Lanka, to increase the forest cover in the region and to improve the social status of the poor in these areas. Rubber growing soils in the traditional areas have been evaluated for their nutritional status and it is imperative that the application of N, P, K and Mg in correct proportions is essential to obtain optimum yields in these areas. Different fertilizer mixtures have been formulated for the three broad soil groups in the traditional rubber growing areas (Silva, 1971). Such studies have so far not been conducted for the rubber grown in the Moneragala region. Fertilizer mixtures formulated for rubber growing soils in the Low country Wet zone (traditional areas) are being applied by the rubber growers in the Moneragala district. A urea based NPK fertilizer mixture (R/U/12:14:14) is used in this region with a Mg fertilizer at rates applied to the traditional rubber growing soils
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