Biochar and vermicompost amendments in vegetable cropping systems:Impacts on soil quality, soil-borne pathogens and crop productivity
Amending soils with biochar and vermicompost has the potential to provide multiple benefits for specialty crops including pathogen suppression and increased crop productivity. Oomycete pathogens such as Phytophthora capsici can devastate crop fields and they are difficult to control presenting significant management challenges for Midwestern growers. Soils amended with a microbially-inoculated softwood biochar increased carrot root growth relative to the control and corn stover biochar in 2011, while the corn stover biochar also increased carrot root growth relative to the control, but only in two varieties. Neither biochar treatment influenced carrot growth in 2012. In greenhouse trials, vermicompost amendments provided little nitrogen and pepper growth was reduced compared to treatments that received Osmocote fertilizer. We observed some evidence of nitrogen immobilization in response to both biochar amendments, though not enough to influence pepper productivity. Both biochar amendments increased soil pH relative to the control, and vermicompost increased soil pH relative to biochar treatments in all three soils tested. The softwood biochar amendment reduced fluorescein diacetate (FDA) enzyme activity alone and in combination with the vermicompost relative to the control in all soils, which could have resulted from enzyme sorption. The softwood biochar increased shoot length and root dry weight relative to the control in soil P, but not in the other two soils. The microbially-inoculated softwood biochar reduced P. capsici soil populations in two of the three soils tested, and coupling this biochar with vermicompost resulted in reduced soil P. capsici populations in all three soils. The microbial-inoculated softwood biochar also decreased P. capsici root infection relative to the control in two of the three soils tested. Coupling biochar amendments with vermicompost also reduced P. capsici root infection in two soils, with the microbially-inoculated softwood biochar reducing infection in one soil, and the softwood biochar reducing infection in the other. These data suggest that biochar and vermicompost amendments can alter soil quality, suppress soil-borne pathogens and increase specialty crop productivity, but benefits depend on the type of biochar applied, and soil and environmental conditions. Further studies are recommended to determine the mechanisms responsible for improved crop growth and oomycete pathogen suppression in response to biochar and vermicompost amendments. Understanding how soil properties and plant-microbe interactions respond to biochar and vermicompost will provide greater insight into the mechanisms regulating these beneficial effects, and provide the knowledge needed to develop new management strategies for Indiana vegetable growers. Bioassays that identified a virulent P. capsici isolate will benefit future studies investigating biocontrol of this important oomycete pathogen.
Hoagland, Purdue University.
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