Abstract
Abstract Apple replant disease (ARD) is a specific apple-related form of soil fertility loss due to unidentified causes and is also known as soil fatigue. The effect typically appears in monoculture production sites and leads to production decreases of up to 50%, even though the cultivation practice remains the same. However, an indication of replant disease is challenged by the lack of specification of the particular microbial group responsible for ARD. The objective of this study was to establish an algorithm for estimating growth suppression in orchards irrespective of the unknowns in the complex causal relationship by assessing plant-soil interaction in the orchard several years after planting. Based on a comparison between no-replant and replant soils, the Alternaria group (Ag) was identified as a soil-fungal population responding to replant with abundance. The trunk cross-sectional area (CSA) was found to be a practical and robust parameter representing below-ground and above-ground tree performance. Suppression of tree vigour was therefore calculated by dividing the two inversely related parameters, Q = ln(Ag)/CSA, as a function of soil-fungal proportions and plant responses at the single-tree level. On this basis, five clusters of tree vigour suppression (Q) were defined: (1) no tree vigour suppression/vital (0%), (2) escalating (−38%), (3) strong (−53%), (4) very strong (−62%), and (5) critical (−74%). By calculating Q at the level of the single tree, trees were clustered according to tree vigour suppression. The weighted frequency of clusters in the field allowed replant impact to be quantified at field level. Applied to a case study on sandy brown, dry diluvial soils in Brandenburg, Germany, the calculated tree vigour suppression was −46% compared to the potential tree vigour on no-replant soil in the same field. It is highly likely that the calculated growth suppression corresponds to ARD-impact. This result is relevant for identifying functional changes in soil and for monitoring the economic effects of soil fatigue in apple orchards, particularly where long-period crop rotation or plot exchange are improbable.
Highlights
Intensive monoculture production involves the continuous replanting of crops at the same location
The increase in CSA40 plateaued towards a maximum at a relationship of 200 cm2 to 200 thousand pixels/unit area
The planting years differed by 26 years, the vegetative plant performance of single trees overlapped within a range of CSA40 from 150 to 220 cm2 and the above-ground tree area from 140 thousand to 200 thousand pixels/tree area
Summary
Intensive monoculture production involves the continuous replanting of crops at the same location. The resulting loss in productivity and yield is known as soil fatigue (Wolińska et al, 2018), soil sickness (Cesarano et al, 2017) or replant disease (Nicola et al, 2018). Specific apple replant disease (ARD) is found in mother plant plantations, plantations for the cultivation of rootstocks, and plantations for line-out after grafting as well as in orchards. ARD has been found to suppress vegetative and generative performance of apple orchards by up to 50%, to reduce fruit size by up to 10% and to delay the bearing of fruit on trees by 2–3 years (Nicola et al, 2018; Mazzola and Manici, 2012; Mazzola, 1998)
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