EFFECTS OF COMPOST AND MILL MUD/ASH ON SOIL CARBON AND THE NEMATODE COMMUNITY IN A FIELD TRIAL ON SUGARCANE AT HARWOOD, NEW SOUTH WALES

A FIELD TRIAL at Harwood, New South Wales compared an amendment of mill mud/ash with compost produced from mill mud/ash, bagasse and wood waste. The trial contained 13 treatments (compost at 13, 26, 55 and 66 dry t/ha; mud/ash at 15, 30, 58 and 90 dry t/ha; and urea at 0, 40, 82, 140 and 230 kg N/ha). Data collected from the two-year-old plant crop showed that both amendments improved sugarcane yield and that the response increased as the amendment rate increased. Analyses of soil organic carbon following plant crop harvest showed that both mud/ash and compost increased total carbon levels by 7?10%. Given the central role of carbon in improving a soil?s physical and chemical properties, this increase was probably one of the reasons yield responses were obtained. However, data obtained from analyses of the nematode community indicated that biological factors were also involved. Two years after the mud/ash was applied, populations of root-lesion nematode (Pratylenchus zeae), an economically important pest of sugarcane, were reduced by about 60%, while compost increased populations of microbivorous nematodes, a group of nematodes that improve plant nutrition through their involvement in nutrient mineralisation processes. Analyses undertaken after the ratoon crop was harvested two years later showed that soil carbon levels in the amended soils were still significantly higher than the non-amended control and that both amendments had reduced populations of stunt nematode (Tylenchorhynchus annulatus), one of the five plant-parasitic nematode found at the site.