Recycled shrimp waste water tested as fertilizer

Shrimp water beats vermicompost for pepper production

Mississippi is one of the largest farm-raised shrimp-producing states in the U.S. In addition to producing bountiful quantities of shrimp, the industry generates significant amounts of wastewater that is rich in nutrients. The effluent waters that are byproducts of shrimp farms could be harmful to ecosystems if released into rivers and streams, but hold promise if recycled and used as fertilizer.

"Research on finding new uses of the wastewater from shrimp aquaculture systems would be beneficial to the aquaculture industry and to the environment," explained Valtcho D. Zheljazkov, who along with other colleagues designed experiments to see if shrimp waste water could be used successfully as a fertilizer. "To our knowledge, this was the first study using shrimp water as a nutrient source for bell peppers," the researchers noted.

The experiments featured pepper plants exposed to one of 12 treatments. The control group was irrigated with tap water and not fertilized. Another group was irrigated with the water from the shrimp tanks. Two more groups were treated with either a controlled-release fertilizer or a water-soluable fertilizer. The eight remaining groups received vermicompost fertilizer at 10%, 20%, 40%, or 80% with or without shrimp water.

Ripe peppers were continually picked, weighed, and analyzed for nutrient content. Once all of the peppers were harvested, the soil was measured for nutrient content.

The researchers' results (published in HortScience), found that plants fertilized with either of the chemical fertilizers--controlled-release or water-soluable formulas--produced the most peppers, the most peppers per plant, and the heaviest peppers. The combination of vermicompost and shrimp water yielded more peppers than the control. Shrimp water alone had better yields than vermicompost at 10% and 80%, but none of the alternatives matched the nutrient availability of the chemical fertilizers.

Shrimp water also came up lacking in terms of nutrients; nutrient levels in shrimp water were similar to those in vermicompost. "The results suggest that shrimp water and vermicompost application to bell peppers must be supplemented with another nitrogen source," the study reports.

The report also noted that measuring nutrients in the growing medium was not a good predictor of nutrients in bell peppers. Out of several nutrients measured including iron, magnesium, zinc, and calcium, only potassium levels in soil correlated with those found in the peppers.

Publication date: Fri 6 Sep 2013