Impact of biochar application on gas emissions from liquid pig manure storage

Highlights: • Nitrogen losses of liquid manure were enhanced with biochar application. • Greenhouse gas emissions of liquid manure were increased with biochar application. • The absorption of biochars played minor role in manure nitrogen conservation. Biochars have been used to reduce gas emissions from manure composting practices and to recover nutrients from wastewater because of their effective sorption capacity. However, relatively less is known about the impacts of different alkaline biochars on the gas emissions from liquid manure. Materials including two commercial biochars prepared from walnut shell (WA) and coconut shell (CC), respectively, and coal (CO) were applied (with manure/biochar ratio of 20:1 in weight) to examine their influence on NH₃, CH₄, and N₂O emissions from liquid pig manure during a 68-d period in comparison with a control (CK, without biochars), and to investigate the evolution of the manure N mass balances and the changes in biochar properties during liquid manure storage to understand the characteristics of biochar. Compared with the CK, the application of WA, CC, and CO biochars increased the NH₃ emissions by 4.00, 3.87, and 1.23 times, respectively, the absorbed N content of the biochars was markedly lower than the enhanced gaseous losses through NH₃ emissions. Similarly, the total greenhouse gas (GHG) emissions from the manure with WA, CC, and CO biochar application were 6.28, 5.55, and 0.83 times greater than those observed with the CK, respectively, and were mainly attributed to the enhanced CH₄ emissions. The significant contribution (5%–12%) of indirect GHG emissions from the enhanced NH₃-N losses was also identified. The hypothesis for the enhanced gas emissions from liquid manure with biochar addition has been discussed in the present study; however, further investigation in the future is warranted.