Effect of Pre-plant Phosphate Charge and Leaching on Phosphorus Longevity in Soilless Substrate1

Abstract

Abstract There is little information addressing the impact of quantity of pre-plant phosphate charge in soilless substrate and leaching during production on soluble phosphate longevity when post-plant phosphate is omitted. Two experiments were conducted growing Petunia ×hybrida ‘Primetime White' seedling crops over a 42-d period in a sphagnum peat moss-perlite substrate. Phosphate-phosphorus (P) charge levels of 0.03, 0.06, 0.12, and 0.18 kg.m−3 (0.05, 0.10, 0.20 and 0.30 lbs·yd−3, respectively) and 0, 20, and 50% leaching were tested. The first experiment was conducted in winter (late November through December) and the second in spring (mid-March through April). The minimum-targeted, soluble-bulk-solution phosphate-P level of 3 mg.L−1 (ppm) was achieved for 41 d in the winter with a phosphate-P charge of 0.06 kg.m−3 (0.10 lbs·yd−3) and 20% leaching. Longevity for this treatment was 4 d less in the spring. At 0% leaching, the soluble-bulk-solution phosphate-P level was above the minimum target level of 3 mg.L−1 (ppm) for the entire 42-d period in both seasons. Increasing the leaching from 20 to 50% resulted in a loss of longevity by 4 d in the winter and 6 d in the spring. Index words: soilless media, bedding plants, floriculture, Petunia ×hybrida, plant nutrition. Species used in this study: petunia (Petunia ×hybrid var. multiflora Vilm.).