Nutritional status of rubber growing soils in the Moneragala district

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 4 + -N released g -1 hr -1 ) 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. Key words : intermediate zone; Moneragala; nutrients; rubber growing soils; urease activity DOI: 10.4038/jrrisl.v87i0.1811 Journal of the Rubber Research Institute of Sri Lanka, (2005) 87 , 23-35