Effect of different storage methods on physic-chemical properties of pig slurry

Objective  Aiming at the great loss of nitrogen during swine slurry storage process, effects of open and sealed storage on the physic-chemical properties of swine slurry during the storage process were compared in autumn and winter to provide a theoretical reference for swine slurry storage and return to the field.

Method  The effects of open and sealed storage on material transformation, nitrogen loss and harmlessness of pig slurry storage were compared in autumn and winter under laboratory condition. The changes of pH value, electrical conductivity (κ), chemical oxygen demand (COD), NH₄⁺-N content, NO₃⁻- N content, total nitrogen (TN) content, seed germination rate and heavy metal (As, Zn, Cu, Pb and Cd) contents were analyzed.

Result  The pH value first increased and then remained relatively stable, κ, COD, the contents of TN, NO₃⁻-N and heavy metals gradually decreased, NH₄⁺-N content first increased and then decreased gradually, and the seed germination rate gradually increased during the storage of pig slurry. After storage, the proportion of inorganic nitrogen in pig slurry increased significantly (Except for winter open storage). Except Cu and Zn did not meet the requirements of “Water Quality Standard for Farmland Irrigation” (GB 5084—2021), As, Pb and Cd met the requirements of harmlessness and stabilization. However storage also caused serious nitrogen loss, with the nitrogen loss rates of 79.44% and 52.60% respectively in autumn and winter under open storage. Compared with open storage, sealed storage reduced the pH value of pig slurry, significantly reduced the nitrogen loss and Zn content during storage, especially the NH₄⁺-N loss. The nitrogen loss rate of pig slurry after storage in autumn and winter decreased by 36.14 and 21.30 percentage points respectively compared with open storage. However, after storage, the κ of pig slurry was significantly higher than that of open storage, seed germination rate was slightly lower, and there was no significant effect on the contents of other heavy metals (As, Cu, Pb and Cd).

Conclusion  Although open storage is simple and convenient, but the nitrogen loss is serious, which reduces the fertilizer value of pig slurry after storage. Therefore, farms should be encouraged to store pig slurry in sealed condition.