Abstract—

The distribution, mineralization, and transformation of soil organic phosphorus (P) exhibits strong regional characteristics because of variations in climate and pear varieties in Yanbian apple–pear orchard. Soil samples were collected in 11, 25, 40, and 63-year-old apple-pear orchards, at the depths of 0–20 cm, 20–40 cm, and 40–60 cm. Soil aggregates were sieved using the dry sieving method, and the concentrations of organic P were determined using the improved Bowman-Cole method. Differences in organic P in soil aggregates were analyzed in respect to planting year, soil layer, and season. According to the results, with an increase in planting years, labile, moderately labile, moderately stable, highly stable, and total extracted organic P in soil aggregates increased and then decreased. The concentrations were the lowest in the 11-year-old orchard and the highest in the 25-year-old orchard. With an increase in soil layer depth, all the forms of organic P concentrations in soil aggregates decreased linearly, and there were significant differences among different levels. In addition, with shifting seasons from spring, summer, to autumn, the labile organic P concentrations in soil aggregates decreased gradually, and the moderately labile, highly stable, and total extracted organic P concentrations first increased and then decreased, while the moderately stable ones first decreased and then increased. All the forms of organic P concentrations in soil aggregates were the highest in the <0.25 mm aggregate size fraction, followed by the 0.25–0.5 mm fraction. The concentrations of total extracted organic P decreased with an increase in aggregate size fraction. According to the results, organic P is accumulated relatively easily in smaller aggregates, and moderately labile organic P was the major form of organic P in the apple-pear orchard soil, followed by highly stable organic P.