TEMPERATURE AND PHOSPHORUS SOURCE AFFECT PHOSPHORUS RETENTION BY A PINE BARK-BASED CONTAINER MEDIUM

These studies were conducted to determine the effect of 1) temperature on P leaching from a soilless medium amended with various P fertilize rs, 2) water application volume on P leaching, and 3) various fertiliz ers on P leaching during production and growth of marigolds (Tagetes e recta L. 'Hero Flame'). Increasing temperature linearly decreased leac hing fraction; however, total P leached from the single (SSP) or tripl e (TSP) superphosphate-amended medium did not differ regardless of tem perature. Despite a smaller leaching fraction at higher temperatures a nd no change in the total P leached, P was probably leached more readi ly at higher temperatures. More P was leached from the medium amended with uncoated monoammonium phosphate (UCP) than from the medium contai ning polymer-coated monoammonium phosphate (CTP at all temperatures, a nd more P was leached from UCP-amended medium at lower temperatures th an at higher temperatures. More P was leached from TSP- than from SSP- amended medium and from UCP- than from CTP-amended medium regardless o f the water volume applied, but leachate P content increased Linearly as water application volume increased for all fertilizers tested. Plan t dry weights did not differ regardless of P source. Leachate electric al conductivity (EC) was lower with TSP than with SSP. Leachate EC was also lower with CTP than with UCP. A higher percentage of P from cont rolled release fertilizer was taken up by plants rather than being lea ched from the medium compared to P from uncoated fertilizers.