Preplant Soil Incorporation of Compost to Mitigate Replant Disease: Soil Biological Factors Associated with Plant Growth Promotion in Orchard Soil
Watson, T.T., Nelson, L.M., Forge, T.A. (2018). Preplant Soil Incorporation of Compost to Mitigate Replant Disease: Soil Biological Factors Associated with Plant Growth Promotion in Orchard Soil. Compost Science & Utilization, [online] 26(4), 286-296. http://dx.doi.org/10.1080/1065657X.2018.1540953
Plain language summary
When new cherry and apple orchards are replanted into old orchard sites, roots of young trees are attacked by plant-parasitic nematodes, which are microscopic roundworms that infect fine roots and inhibit growth of young trees. Historically, growers could treat soil with broad spectrum fumigants before replanting to suppress nematodes and fungal pathogens. Environmental issues associated with fumigants has prompted research to identify soil amendments that can suppress nematode populations and improve early growth of replanted trees without impacting the environment. In previous research we demonstrated that incorporating compost into soil before replanting suppressed parasitic nematode populations and improved early growth of cherry trees at a site in the Okanagan Valley of British Columbia. In order to determine if these benefits can be obtained with different composts in different types of soils, we compared three different composts in each of three different orchard soils with respect to their effects on: apple seedling growth, infection of apple roots by parasitic nematodes, and activity of beneficial soil microbes. In four of the nine compost x soil type combinations, compost improved apple seedling growth relative to untreated soil. In four combinations, compost reduced nematode infection relative to untreated soil, and in one combination compost increased nematode infection. Composts stimulated overall soil microbial activity and abundance of beneficial bacteria in seven of the nine compost type x soil combinations. Overall, our results indicate that composts are not always effective at suppressing parasitic nematode populations and promoting tree growth in a range of soil types.
Preplant soil incorporation of compost has previously shown potential to suppress Pratylenchus penetrans populations and improve replant establishment of newly planted fruit trees at old orchard sites. Using a greenhouse experiment, we evaluated the effects of preplant incorporation of three compost amendments (agricultural waste compost, yard trimmings compost, and municipal waste compost) on growth of apple seedlings, P. penetrans populations, microbial populations associated with soil suppressiveness, and microbial activity using soil collected from three orchard sites. We also aimed to identify the biological factors that were most strongly associated with enhanced plant growth in compost-amended soil. In four out of nine compost type × soil combinations, compost improved apple seedling growth relative to the control. In four out of nine compost type × soil combinations, compost reduced P. penetrans root infestation relative to the control, and in one compost type × soil combination, compost amendment increased P. penetrans root infestation. Composts stimulated soil microbial activity and abundance, resulting in greater populations of Pseudomonas spp. in soil in seven of the nine compost type × soil combinations. In a step-wise multiple linear regression, P. penetrans root infestation and the total abundance of fungi in soil accounted for the most variance in plant biomass, with increases in both variables correlated with reduced seedling biomass. Overall, composts show variability in the capacity to promote the establishment of fruit trees in orchard soil. Future research should be directed toward understanding variability in compost-induced plant growth promotion among different orchard soils and compost types.