Modified lignite and black coal reduce ammonia volatilization from cattle manure

Modified lignite and black coal (BC) are potential amendments for animal bedding to abate ammonia (NH₃) emissions due to their large adsorption capacities for ammoniacal nitrogen (N). However, the ability of modified lignite and BC in reducing NH₃ volatilization from livestock manure and the underlying mechanisms remain unknown. The present study has investigated the effect of lignite, modified lignite, BC and modified BC on NH₃ volatilization from cattle manure, biological immobilization of manure ammoniacal N and manure properties. Modified lignite and BC reduced the NH₃ volatilization from manure by 44 and 36%, respectively, which were comparable with original lignite (43%). The biological immobilization of applied stable isotope labelled ¹⁵N in lignite, modified lignite, BC and modified BC amended manures was 15, 18, 11 and 16%, respectively, which were significantly higher than that in unamended manure (4%, P < 0.001). In addition, NH₄⁺-N concentrations of lignite, modified lignite and modified BC amended manures (7.0-7.3 mg g^-1) were significantly higher than that of the unamended and original BC amended manures (3.3 and 4.8 mg g^-1, respectively, P < 0.001). However, the manure pH in all treatments remained alkaline (pH > 8.2). Our results highlight that the adsorption and immobilization of manure ammoniacal N induced by amendments are the key drivers in reducing NH₃ loss from manure, outweighing the pH effect. The findings of this study provide new insights into the mechanisms of coal amendments reducing NH₃ loss from animal manure and their potential applications in intensive livestock systems.