Soil management in organic production systems.

Central to organic production are soil management strategies to maintain soil fertility and increase soil biological activity by increasing soil organic matter content. An experimental orchard of ‘Ambrosia’/B9 apple (Malus ×domestica) planted at 1 m (within row) × 4 m (between rows) in April 2006 was managed organically for the first six growing seasons. Four randomized organically acceptable soil management treatments, replicated six times in 10-tree plots, were maintained. In-row treatments included 1) annual compost application with tillage for weed control; 2) in row application of alfalfa (Medicago sativa L.) grown between the rows; 3) shredded bark mulch plus in row application of mixed hay grown between the rows; and 4) black plastic mulch, the last two treatments receiving annual fish fertigation to supply 5 g N tree-1 year-1. Adequate tree vigour and leaf N were maintained for trees in all treatments. The most vigorous trees were observed in the bark mulch treatment which had decreased leaf N in the first three growing seasons, but elevated leaf P and K. Fruit yield and quality were minimally affected by soil management. Soil samples collected at the end of the sixth growing season, 0-10 cm depth, indicated all treatments resulted in higher soil organic matter and microbial biomass relative to soil from the herbicide strip of conventionally managed orchards. Soil beneath the bark mulch had the highest available soil P, P-solubilizing phosphatase enzyme, total, mineral- and particulate- associated C concentration.