Phosphorus leaching potential from compost amendments in a carbonatic soil

Composts are applied to carbonatic soils in south Florida to improve their physical characteristics and increase water retention. Blends of biosolids and municipal waste are often combined to increase the nutrient content of the compost. However, the high P content of some compost has led to concerns about the potential for P movement into shallow groundwater. Studies were conducted to determine the potential for P leaching in soil amended with biosolids, clean organic waste, and Bedminster composts. Bedminster was the most suitable of the composts used in terms of a lower potential for P leaching as a result of P sorption in the amended soil. Each compost-amended soil demonstrated a slight decrease in P leaching at 1 pore volume after simulated rainfall (21 cm). Pore volume was defined as the total volume in a column less the volume of solids. The high P content of the composts made it unlikely that additions of these materials to soil would improve P sorption capacity. However, Bedminster and clean organic waste did not significantly increase P leaching above that of the soil. Caution should be exercised when applying these composts because materials themselves contain an enormous amount of P that could be eventually transported into the groundwater.