Multi-year effects of Brassicaceae seed meal and anaerobic soil disinfestation treatments on apple tree growth and yield at replant orchard sites

Seed meal soil amendment and anaerobic soil disinfestation treatments have shown promise as alternatives to fumigation for the control of apple replant disease. In a previously published study, we evaluated the efficacy of Brassicaceae seed meal and anaerobic soil disinfestation in four experiments for the control of apple replant disease at a commercial scale across three orchard locations. Both biorenovation techniques resulted in significant changes to the rhizosphere microbiome in three of four experiments. First year tree growth in Brassicaceae-amended soils was as great or greater than in fumigated soils, and in anaerobically-disinfested soils, was greater than no-treatment controls in three of four experiments. In this paper we report tree growth and yield impacts of these experiments six years after planting. Trees grown in Brassicaceae-amended soils resulted in higher annual yield in three of four location-rootstock comparisons and cumulative yield in one of four location-rootstock comparisons. Trees grown in anaerobic soil disinfestation treated soils resulted in higher annual yield in two of four location-rootstock comparisons and cumulative yield in one of four location-rootstock comparisons. Annual and cumulative yield values corresponded with differences in tree growth. Promotion of tree growth was primarily observed during the first year, with tree size remaining larger over time as a result of the initial growth improvement. The return on investment for Brassicaceae seed meal in Washington was not as high as fumigation in this study, but further research on reduced rates, as well as changing regulatory and economic environments, make bio-renovation a potentially useful forthcoming tool.