Organic Amendments Enhance Biological Suppression of Plant-parasitic Nematodes in Sugarcane Soils

Previous research has shown that population densities of plant-parasitic nematodes are reduced when a legume crop is grown in rotation with sugarcane. However, this effect is only temporary, as nematodes usually return to high densities within 12 months of planting sugarcane. This rapid resurgence suggests that natural enemies that normally keep plant-parasitic nematodes under control in natural environments may be depleted by the soil-management practices used to grow sugarcane. This paper describes an experiment in which organic materials were added to sugarcane soils in an attempt to enhance biological activity and increase the suppressiveness of soils to plant-parasitic nematodes. The amendments used were sawdust, sugarcane trash, grass hay and legume hay with or without nitrogen, and feedlot manure, poultry manure, chitin and mill mud without additional nitrogen. The chemical and biological changes occurring during the decomposition process were monitored for 12 months, while the capacity of amended soils to suppress lesion and root-knot nematodes was assessed periodically using bioassays. Seven months after amendments were incorporated, soils amended with sawdust, sugarcane trash or grass hay were more suppressive to root-knot nematode than soils amended with nitrogenous materials. Sugarcane grown in soil amended 6 months previously with sawdust, sugarcane trash, grass hay or lucerne hay had 78%, 61%, 96% and 92%, respectively, fewer lesion nematodes in roots than sugarcane growing in non-amended soil. Low concentrations of nitrate nitrogen in the soil, a fungal dominant soil biology and high numbers of omnivorous nematodes were most closely associated with suppression. These results indicate that the biology of sugarcane soils can be altered by changing the quality and quantity of organic inputs. Amendments with high C/N ratios are most effective in enhancing biological control activity against plant-parasitic nematodes. Stirling, G.R., Wilson, E.J., Stirling, A.M., Pankhurst, C.E., Moody, P.W. and Bell, M.J. Proc. Aust. Soc. Sugar Cane Technol., Vol. 25, 2003 _______________________________________________________________________________