Bio-solids as Organic Fertilizer for Pastures
Bio-solids have been used as an organic fertilizer source for centuries. Bio-solids in Florida are graded in three general categories: AA and B. The safest grade is AA, this grade has the lowest metals and pathogens. This grade of Bio-solids meets the standard that is set for application of products on lawns, play grounds, and ball fields.
Research at the University of Florida Range Cattle Research and Education Center in Ona, Florida has shown that, when used at the recommended amounts of up to 160 pounds of available nitrogen per acre they are safe. Bahia grass fertilized with Bio-solids or mineral (chemical) fertilizer yield increased by 100% over areas that received no fertilizer in test. The cumulative yields between the fertilizer sources were similar. Application of Bio-solids had no significant impact on water quality or greenhouse gas emissions. The application of mineral fertilizer resulted in large peaks of nitrogen and phosphorus soon after application. Nitrous oxide and carbon dioxide emissions were also elevated after mineral fertilizer was used.
Similar results were found in earlier trials. In these trials ground water was monitored. Various levels of nitrogen fertilizer from commercial fertilizer was compared to that of Bio-solids sources. A slight increase was observed in both nitrogen and phosphorus in ground water under the plots after Bio-solid based fertilizer was used. When commercial mineral based fertilizer was used high peaks in nitrogen and phosphorus were observed shortly after application. The growth curve of the Bahia grass also flatten giving the same amount of grass but over a longer period of time indicating a slower release of nutrients from the Bio-solids.
Many treatment plants use lime to treat Bio-solids. Although most soils in Florida require the addition of lime to raise the pH, excessive high level of lime can raise soil pH above 8. Pasture grasses grow best in a range of 5.0-7.0. Above 7.0 it is difficult to grow grass. Monitoring the soil pH and the pH of the Bio-solids is necessary to keep the soil within the acceptable range.
It appears from these findings that organic fertilizer in the form of Bio-solids is an environmentally sound substitution for commercial mineral fertilizer when used according to UF recommendations.