Compost and Manure Mediated Impacts on Soilborne Pathogens and Soil Quality

Abstract

Root rots of snap bean (Phaseolus vulgaris L.) and sweet corn (Zea mays L.) cause economic losses to farmers. This study was conducted to determine whether dairy manure amendments suppressed root diseases and to describe relationships between disease severity and soil characteristics. Field plots were amended with high or low rates of fresh or composted dairy manure solids in 2001 and 2002. Soils were collected at 2 and 12 mo after the first amendment and 2 and 6 mo after the second amendment. Greenhouse bioassays were conducted to assess severity of damping‐off (DO) of cucumber (Cucumis sativus L.) and root rots of bean and corn. Soils were analyzed for soil free (fPOM) and occluded (oPOM) particulate organic matter content, rate of hydrolysis of fluorescein diacetate (FDA), arylsulfatase activity, microbial biomass C, and water‐stable aggregation (WSA). Two months after amendment, all amendments (except the low rate of manure) reduced the severity of DO 30%, bean root rot 29%, and corn root rot 67%. Twelve months after amendment, amended soils were no longer suppressive. All amendments were suppressive after re‐amendment the following year and no longer suppressive 6 mo later. In Year 1, significant suppression was observed across all diseases when fPOM content was ≥12.1 g cm−3, FDA activity was ≥2.88 μg FDA min−1 g−1 dry wt, and microbial biomass was ≥91.6 μg C g−1 dry wt, and these levels were proposed as suppressive thresholds. Only the FDA threshold held up over all sampling times.