Orchard floor management strategy to maintain performance of apple trees in replant soils

Apple replant disease (ARD) is a consequence of consecutive planting of trees in the same field, e.g., under long-term monoculture conditions. Visible impediments appear in the form of stunted vegetative growth and reduced yields. Strategies to avoid losses in profitability include plant vitalization, selection of non-sensitive plants, and plot exchange. As an alternative measure, a ridge planting method was developed to maintain plant vitality by treating the orchard floor with the layered mulch compound "Muncheberger Dammkultur" (MDK), applied during planting of trees. The aim was to prove its efficacy under commercial conditions of apple production on sandy soils in Brandenburg, Germany. Short-term effects and long-term effects were measured upon initial and repeated application of MDK. The effect was analyzed by vegetative growth, represented by trunk cross-sectional area (CSA) and formation of adventitious roots. Repeated application of MDK on trees on replant soils resulted in a significant increase in trunk CSA as compared to trees with no treatment. Root morphology showed considerable differences in root formation between trees in replant soil with and without MDK treatment. Next to a generally positive impact of MDK on plant growth, particularly in the long term, two basic effects were observed: a) the MDK ridge serves as an additional substrate layer used by adventitious roots, and; b) ARD affected plants on replant soil were observed to shift their growth to the winter period, whereas MDK treatment realigned growth phases to the summer months. Both effects contributed to plant growth in a replant situation with MDK.