DEVELOPMENT OF SUPPRESSIVENESS TO DISEASES CAUSED BY RHIZOCTONIA-SOLANI IN SOILS AMENDED WITH COMPOSTED AND NONCOMPOSTED MANURE

Fresh and composted dairy manure were compared along with other amendments in the greenhouse and in field microplots for their effects on induction of suppression to plant diseases caused by Rhizoctonia solani. Damping-off of radish induced by R. solani was least severe for seedlings planted in the greenhouse in soil media amended with urea and straw, more severe with manure or compost, and most severe after urea treatment. Radish damping-off was less severe at all inoculum density levels in the urea with straw treatment than in the other amendment treatments. At very high infestation levels (20 and 30 cfu/g R. solani), disease severity did not differ among the least effective amendments. The population of R. solani did not differ among treatments, despite differences in radish damping-off severity. Manure and compost were more effective than urea alone in inducing suppression of damping-off of radish at low inoculum levels. Neither amendment was effective at high inoculum levels. Bean hypocotyl lesions were least common for seedlings planted in field microplots amended with manure, and more severe in those treated with compost. Composting of animal manure did not significantly enhance the effectiveness of manure for inducing suppression in soil of plant diseases caused by R. solani.