Nematodes, bacterial activity, soil characteristics and plant growth associated with termitaria in a sugarcane field in South Africa

Abstract

Circular patches of exceptionally well-grown sugarcane, known as "isiduli" are a common feature of sandy sugarcane fields in South Africa. They correspond to termitaria of Macrotermes natalensis, leveled by ploughing of the field. Root and soil samples were collected at 0-30 and 30-60 cm depths along a 21m transect, which passed through an isiduli. Soil physical and chemical analyses were made. Nematodes in the soil and roots of cane were identified and counted and bacterial activities were measured. Plant characteristics were determined at the various points along the transect and chemical analyses of the leaves were performed. Estimated cane yield was five times greater within the isiduli than elsewhere along the transect. Levels of N, Si, S and Ca were higher in the leaves of cane within the isiduli than outside. The reverse was true for Mn, juice purity and % sucrose. Meloidogyne javanica was absent and Xiphinema elongatum less abundant in the isiduli than elsewhere. Greater numbers of Helicotylenchus dihystera, Pratylenchus zeae and Paratrichodorus spp. occurred within the isiduli than elsewhere along the transect. The limits of the contrasting nematode communities closely matched the limits of the isiduli as defined by the vegetative parameters. The levels of the different soil elements in the topsoil (0-30 cm) were always higher within the isiduli. However, the extent of the isiduli, when defined by the greater concentrations of soil elements, did not correspond well with the limits determined by the vegetative parameters. A better correspondence was observed with the soil characteristics of the deeper (30-60 cm) soil layer. Bacterial activity gave the poorest discrimination of the extent of the isiduli, high bacterial activity being observed in samples collected both inside and outside the isiduli.