MARIGOLD GROWTH AND PHOSPHORUS LEACHING IN A SOILLESS MEDIUM AMENDED WITH PHOSPHORUS-CHARGED ALUMINA

Alumina granules charged with P were used as an amendment to improve t he ability of a soilless medium to retain P and provide it to plants. Commercially available alumina was acidified, saturated with P, and ev enly distributed in a medium of peat, vermiculite, and sand to grow po tted marigolds (Tagetes spp.) to a commercially salable stage. Marigol ds grown in medium amended with P-charged alumina had adequate nutriti on and similar or superior shoot growth (as measured by height, number of branches, and flower production) and fresh and dry weights compare d to marigolds grown using commercial fertilizer. phosphorus-charged a lumina at 1% or 2% of total medium volume was sufficient to grow marig olds for at least 8 weeks and substantially reduced P leaching compare d to conventionally fertilized controls. Alumina amendments in this ra nge did not cause Al toxicity, as evidenced in root growth and leaf Al content.