A surface mulch of crop residues enhances suppressiveness to plant-parasitic nematodes in sugarcane soils

Abstract

Most Australian sugarcane crops are harvested green, with the crop residues left behind after harvest remaining on the soil surface as mulch, a process known as green cane trash blanketing. Sampling in trash-blanketed sugarcane fields showed that roots were present to a depth of 150 cm, but that more than 90% of the root biomass was in the upper 30 cm of the soil profile. Many of these roots were concentrated in a layer just below the trash blanket and they were unusually healthy, presumably because population densities of Pratylenchus zeae/g root were 5-16 times lower than in roots a few cm further down the profile. Results of a microcosm experiment indicated that mulching soil with sugarcane residue increased soil C, microbial activity and numbers of free-living nematodes, and enhanced suppressiveness to Meloidogyne javanica and P. zeae to a greater extent than incorporating the residue into soil. It is hypothesized that roots immediately beneath the trash blanket remain healthy because C inputs from root exudates and organic matter on the soil surface sustain a soil food web capable of suppressing root pathogens, including plant-parasitic nematodes.