Solid Effluent from Thermophilic Anaerobic Digestion of Poultry Litter as a Potential Fertilizer

Abstract

Fertilizer costs and increased awareness of non-point source pollution run-off amplify the pressures on farm economics. Intensive farming operations provided the impetus for our study using effluent from anaerobic thermophilically digested poultry litter as a potential fertilizer. Five fertilizer treatments were used: unfertilized control, pelletized municipal sludge, commercial crop specific products, 1x digested solids and 2x digested solids. All four applications of fertilizer were equalized for nitrogen based on commercial product recommendations. Beds treated with 2x solids accumulated higher percentage of organic matter over the 5-year period. A statistically significant increase in phosphorus was found in the solids beds in 2003. Beds with 2x solids showed statistical significance for Mg, Zn and Cu. Fertilizer trials included blueberries, tomatoes, potatoes, and sweet corn. Potato fresh weight was not significantly different in 2002 or 2003, but was in 2001. Tomato fruit number was not significantly different in 2001 or 2003, but was in 2002. Tomato fresh weight for 2x solids was not significantly different from the commercial or pelletized sludge treatments in 2002 and 2003 suggesting that tomato may discriminate between treatments. Commercial and pelletized sludge fertilizers were statistically better for sweet corn fresh ear weight and number of ears in 2002 and 2003. Blueberry yields were not significantly different between treatments for any year. As this is a perennial crop, it may be several years before a significant difference is observed. While not a total solution, our research shows the effectiveness of digested poultry litter as part of a nutrient management program; making livestock residuals a nutrient resource which offers the potential for organic use.