Use of a wheat straw covering to reduce nitrogen loss during pig slurry storage and reuse of the straw covering in biochar production for nitrogen retention in the slurry

Storing pig slurry (PS) and returning it to the field is one of the most important ways to recycle PS. However, during the storage of PS, the NH₃ emissions cause a large loss of nitrogen (N), which reduces the fertilizer value of stored PS and cause environmental pollution. To reduce N loss during PS storage, we added different amounts of wheat straw powder (WSP) and wheat straw segments (WSSs) to the PS. The wheat straw cover was used for biochar production, and then, the biochar was used for N adsorption from the PS. The results showed that the N loss of PS was significantly decreased by use of the wheat straw covering. The N losses in treatments of WSP covering and WSSs covering were reduced by 4.8–53.1 and 0.8–14.2 percentage points compared with that in the control, respectively. Ammonia adsorption is an important reason for the reduction in N loss by straw covering during PS storage. After covering for 180 days in storage, the NH₄⁺-N content in both the WSP covering and WSSs covering increased greatly, and the cover was reused for biochar production. The biochar yield was inversely proportional to the pyrolysis temperature, and the specific surface area and pore volume of the biochar were proportional to the pyrolysis temperature. We achieved the highest amount of NH₄⁺-N adsorption (1.9 mg/g) with a biochar dosage of 0.2 g/L (treatment Y-400). This study provides a new straw-covered PS storage method to achieve straw recycling and low N loss during PS storage.