Phosphorus and Sulfur Leaching from an Incubated Superphosphateamended Soilless Container Medium

A 2 pine bark : 1 moss peat: 1 sand (by volume) medium (11% volumetric, 20% gravimetric moisture) amended with 4.2 kg m −3 of dolomitic limestone and 3 kg m−3 of 32P-, 35S-superphosphate (8.7% P, 11.7% S) was incubated (25°C) for either 0, 15, or 30 days. Columns (4 × 15 cm) of the medium for each incubation time received 48 ml of deionized water (pH 5.5) in 3 hr on day 1 and 16 ml in 1 hr on days 2-21. Forty-six and 21% of 32P and 35S, respectively, leached on day 1 when the medium was not incubated. Thirty-one percent and 28% of the 32P and 14% and 13% of the 35S leached on day 1 if the medium had been incubated 15 or 30 days, respectively. Eighty-two percent of the 32P and 66% of the 35S amendment leached from the unincubated medium during the 3 week experimental period. A similar leaching experiment, but with superphosphate in absorbent cotton instead of the soilless medium, indicates superphosphate dissolves readily.