Estimating the availability of nutrients from processed swine lagoon solids through incubation studies

Potential environmental hazards from the excess accumulation of swine (Sus scrofa domesticus) manure in eastern North Carolina and new state guidelines on treatment alternatives have necessitated the reevaluation of best management practices for disposal of swine waste (manure and e‚uent) as a fertilizer source on local crop land. Creation of a value-added product is one viable means of utilizing and economically redistributing the nutrients in swine manure. Incubation studies using four agricultural soils from eastern North Carolina were conducted with pelletized processed swine lagoon solids (PSLS) (1.7% N, 2.5% P, 0.12% Cu and 0.18% Zn) composed of dewatered swine lagoon sludge plus rock ¯our. The PSLS was added at three application rates (0, 200, 400 mg N kgÿ1 soil) and incubated for 16 weeks at 25°C. The soil was sampled at 0, 1, 2, 4, 8, 12, and 16 weeks and analyzed for NO3±N, NH4± N and Mehlich III-extractable P, Zn, and Cu. High concentrations of NH4±N and low concentrations of NO3±N were present in the soils shortly after addition of PSLS. After the second week, extractable NH4±N dropped to <4 mg kgÿ1, while the soil concentration of NO3±N increased rapidly. The amount of NO3±N generated reached 90% of its ®nal value after the fourth week. Across the four soils, 24±35% of the added N, 15±50% of the added P, 20±50% of the added Zn and 15±20% of the added Cu was extractable after 8 weeks. The PSLS is an excellent source of P, but may require additional N if used as a fertilizer source for most row crops