Relationship between soil alteration index three (AI3), soil organic matter and tree performance in a ‘Cripps Pink’/M7 apple orchard

Abstract

Alteration index three (AI3), which calculates the balances between three microbially-secreted enzymes, potentially enables differences between soils due to contrasting management practices to be quantified in relative terms. The ability of AI3 to distinguish between apple orchard soils under conventional and organic production protocols, and to reflect tree performance, were tested in a maturing ‘Cripps Pink’/M7 apple orchard. Activities of β-glucosidase, phosphatase and urease were determined colourimetrically in extracts of tree-row top-soils (0–15 cm) taken during September and January over five consecutive seasons. Soil organic matter content was determined by dichromate oxidation. Stem circumference and yield were measured manually. AI3 correlated significantly (p = 0.05) with soil organic matter, yield and yield efficiency. AI3 may thus be a useful indicator of relative apple tree performance under organic and conventional soil surface management practices.