ROOT DECOMPOSITION IN TROPICAL GRASSES AND LEGUMES, AS AFFECTED BY SOIL TEXTURE AND SEASON

We aimed to determine how root decomposition is affected; by soil text ure and weather conditions, and to produce a data set for calibrating or validating litter decomposition models. Roots of tropical grasses a nd legumes were buried in the field in two acid Oxisols of widely diff ering textures during either the dry or the wet season. Results were a nalyzed, using four decay models: single exponential, single exponenti al with residue, double exponential, and a model in which the relative decomposition rate (RDR) decreases non-linearly as a function of the litter fraction left: 1/X.dX/dt = -k(X/X-0)(1/b) In the dry season, th e RDR of all roots decreased steeply with a declining fraction of left over root weight. This indicates a rapid loss of a small fraction of e asily decomposable material, leaving behind a large fraction of recalc itrant material. In the wet season, RDR decreased more gradually. The basic pattern of decomposition was the same for both clay loam and san dy soil, although the absolute values for RDR and the steepness of its decrease differed. Given that the two soils differed widely in textur e and consequent water retention characteristics, the differences in R DR may have resulted from differences in soil water regime. The very h igh C-to-P ratios in the roots (up to 1780) reflect low P availability in these strongly P-sorbing Oxisols. Because microbial C-to-P ratios in these soils ranged from 34 to 50, considerable P immobilization may be needed for decomposition to proceed. Thus, P is likely to be an im portant rate-controlling factor in litter decomposition in these soils . (C) 1997 Published by Elsevier Science Ltd.