ORGANIC AMENDMENTS ENHANCE BIOLOGICAL SUPPRESSION OF PLANT-PARASITIC NEMATODES IN SUGARCANE SOILS

摘要

Previous research has shown that population densities of plant-parasitic nematodes arernreduced when a legume crop is grown in rotation with sugarcane. However, this effect isrnonly temporary, as nematodes usually return to high densities within 12 months ofrnplanting sugarcane. This rapid resurgence suggests that natural enemies that normallyrnkeep plant-parasitic nematodes under control in natural environments may be depletedrnby the soil-management practices used to grow sugarcane. This paper describes anrnexperiment in which organic materials were added to sugarcane soils in an attempt tornenhance biological activity and increase the suppressiveness of soils to plant-parasiticrnnematodes. The amendments used were sawdust, sugarcane trash, grass hay and legumernhay with or without nitrogen, and feedlot manure, poultry manure, chitin and mill mudrnwithout additional nitrogen. The chemical and biological changes occurring during therndecomposition process were monitored for 12 months, while the capacity of amendedrnsoils to suppress lesion and root-knot nematodes was assessed periodically usingrnbioassays. Seven months after amendments were incorporated, soils amended withrnsawdust, sugarcane trash or grass hay were more suppressive to root-knot nematodernthan soils amended with nitrogenous materials. Sugarcane grown in soil amended 6rnmonths previously with sawdust, sugarcane trash, grass hay or lucerne hay had 78%,rn61%, 96% and 92%, respectively, fewer lesion nematodes in roots than sugarcanerngrowing in non-amended soil. Low concentrations of nitrate nitrogen in the soil, arnfungal dominant soil biology and high numbers of omnivorous nematodes were mostrnclosely associated with suppression. These results indicate that the biology of sugarcanernsoils can be altered by changing the quality and quantity of organic inputs. Amendmentsrnwith high C/N ratios are most effective in enhancing biological control activity againstrnplant-parasitic nematodes.