Compost Curing Reduces Suppression of Plant Diseases

Prolonged curing of compost reduces risks of phytotoxicity but may also have an undesirable effect on suppressiveness against soil-borne diseases. In a previous study, this effect was demonstrated for a compost produced from a mixture of yard waste and biosolids, against Sclerotium rolfsii. The aim of the present study was to demonstrate that similar effects of prolonged curing may be exhibited by additional types of composts and pathosystems. Therefore, we investigated the effect of curing of three types of composts against S. rolfsii and Pythium aphanidermatum. These plant pathogens are subjected to different suppression mechanisms. The prolonged curing was characterized and validated by measurements of a range of chemical and spectroscopic parameters. All three composts were suppressive against both diseases before curing. At high inoculum levels, suppression against P. aphanidermatum was lost for the cured biosolids and straw and manure based compost. Loss of suppression was associated with a decrease in basal and substrate induced respiration. For S. rolfsii suppression was lost with curing for all three composts and was associated with a decrease in dissolved organic carbon and NH4⁺ concentration, a decrease in pH and an increase in NO3⁻ concentration.