Root distribution pattern of young Swietenia macrophylla King. stands in Central Kerala, India

Abstract

The major constraints to intercropping in woody ecosystems are belowground competitions for water and nutrients which are in short supply. The spatial spread of roots of the trees play major role in this context. The root distribution pattern was examined in a seven-years-old mahogany (Swietenia macrophylla King.) plantation established at 2.5 m × 2.5 m spacing by following logarithmic spiral trench technique. The root intensity steadily declined with increase in root diameter classes. The small roots (<2.5 mm size class) represented the major share of the total root intensity (7566 number m-2), followed by medium sized roots (4713 number m^-2; size class >2.5 to <5.00 mm) and lowest for the coarse roots (406 number m^-2; size class >5.0 mm). Significant variation in root intensity was observed for different soil depths and lateral distances sampled. The roots generally followed decline in intensity with increasing lateral distance from the tree as well as with increasing soil depth. The small root count at the proximal end of the trench (closest to the tree base; 0.39 m) was 2266 while the corresponding count at farthest lateral distance (2.99 m) was only 133. The shallow soil depth of 0-20 cm represented almost 41% of the total small root count. The soil zone lying within 2.17 m lateral distance from the base of the tree and at 50 cm soil depth accounted for almost 84% of the total roots for the S. macrophylla tree studied. This forms the zone of root activity for most of the field intercrops hence could lead to intensive competition with field crops. The observed root distribution for S. macrophylla at seven year age indicates that the probable safer spacing for effective intercropping would be nearest to 5.34 m between trees.