The recovery and behavior of fertilizer nutrients from the anaerobic digestion of poultry manure

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Virginia Polytechnic Institute and State University

Nutrients of animal manures digested anaerobically for biogas production are highly conserved. The objectives of this study are to evaluate changes in the fertilizer value of poultry manure following digestion.

Total kjeldahl N (TKN) was completely recovered during digestion, however, NH₄⁺N was 159 and 151% recovered fran pilot scale plug flow and laboratory scale digesters. This indicates that added organic N is mineralized. Recovered N and K were associated with liquid fractions and P, Ca, Mg and micronutrients were associated with solids of digested slurries.

The mineralization of organic N fran soil applied effluent was 2.3 times greater in comparison to influent over a 33.5 week laboratory incubation period. Higher mineralization is due to segregation of decay resistant solids into the settled sludge and the decrease in surface area of suspended solids during digestion.

Significantly higher NH₃N volatilization (3 fold to 62%) of land applied effluent compared to influent is due to increases in pH and NH₄⁺N:TKN during digestions. Yields of corn (Zea mays L.) grain at two sites were similar for effluent, influent and urea treatments receiving identical N rates. However, the silage yield of the urea treatment was significantly 19.9% higher than that of the effluent at site 1. Yields and ear leaf N were highly correlated with applied N discounted for NH₃N losses. This indicates that organic N of the effluent and influent become plant available during the growing season.