Because sewage sludge is a source of nutrients for crops, and also a potential ground and surface water contaminant, we need to better understand its rate and transformation in soils where it is applied. Consequently losses may occur to the environment. In the past there had been concern over heavy metal contamination from sludges. Over the past 30 years sludges have become substantially cleaner and thus heavy metal contamination of the environment from sludge application is of little concern. The concentrations of nutrients and heavy metals in sludge should be provided by the suppliers.
Sewage sludge is an organic slow release fertilizer.
Approximately 40 percent of the nitrogen in sludge is available to the plant the first year with the other 60 percent becoming available over time. However, studies are still being conducted at the Ona Research Center to determine the rate of nutrient availability for sludges applied to Florida soils. Using sludge as an organic slow release fertilizer for crops and grasses grown in Florida would be a beneficial source of nutrients compared to inorganic fertilizers which leach more readily than slow release fertilizers in sandy soils. Before sludge can be used by growers in Florida there is a need to demonstrate that it is a safe and viable source of nutrients for crops in Florida. Researchers at the Ona Research Center are currently evaluating the potential of using sludge as a fertilizer for pastures in Florida.