Using organic waste as fertilizer is not a new concept. Before the 1940s, when synthetic nitrogen fertilizer became widely available, animal manure and human waste were commonly used for improving crop yields around the world. This technique is receiving renewed interest as municipalities face increasing waste disposal challenges.

In a study conducted in Florida from 1997 to 2000 and published in the November/December 2002 issue of Agronomy Journal, scientists from the University of Floridas Institute of Food and Agricultural Sciences compared the effects of different kinds of sewage sludge versus commonly used synthetic nitrogen fertilizer on the forage crop bahiagrass.

Researchers Martin B. Adjei and Jack E. Rechcigl studied yield, protein content, mineral content, and digestibility. Accumulation of heavy metals and nutrients in the crops, groundwater, and soil were also evaluated.

Funded in part by the Florida Department of Agriculture and Consumer Services, the study showed liquid forms of sludge are just as effective as traditional synthetic fertilizer. Some minerals such as phosphorus, calcium, and iron were higher in crops fertilized with sludge. In a very dry year, the water in liquid sludge can also enable nutrients to reach the crops rooting zone more effectively than synthetic fertilizer.

Liquid sludge if processed and applied according to specific guidelines has the potential to boost production dramatically. It is low in pathogens, inexpensive, and environmentally safe, said Adjei. Approximately half of Floridas 2.5 million acres of bahiagrass are fertilized with synthetic fertilizer yearly.

Adjei added, "While we did observe negligible traces of heavy metals
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Contact: Sara Uttech
suttech@agronomy.org
608-273-8080
American Society of Agronomy
31-Jan-2003