Effect of compost particle size on suppression of plant diseases.

Abstract Predictability of compost-induced suppression of soil-borne plant diseases is poor. Part of the variability in disease suppression could be due to the heterogeneity of a given compost. Therefore, the disease suppressive properties of different wet-sieved fractions of two composts against three soil-borne plant pathogens were studied. The ability of a green waste and a yard waste compost to suppress the soil-borne plant pathogens Fusarium oxysporum f.sp. lini (host: flax), Phytophthora cinnamomi (host: lupin), and Meloidogyne hapla (host: tomato) was determined. The following compost fractions were prepared: 2–4 mm (40% v/v with peat-based substrate), 1–2 mm (35 or 45% v/v; comparable number of particles and comparable organic matter content as the 2–4 mm fraction amendment respectively), and 1–2 mm (35% v/v) obtained from the 2–4 mm fraction by a series of dry-sieving, crushing, and wet-sieving. The 2–4 mm compost fraction of both composts showed significantly higher disease suppression for the t...