# A Review of Biochar Properties and Their Utilization in Crop Agriculture and Livestock Production
## 4 Biochar as a Manure/Sludge Additive
[PERSON] et al. [41] added 5% and 20% (_w/w_) of pine chips BC to poultry litter that underwent the composting process. Biochar amendment quickened the composting process and emission reductions of H\({}_{2}\)S and NH\({}_{3}\) by 71% and 58%, respectively, were observed for the 20% BC treatment, while 5% BC treatment reduced H\({}_{2}\)S emission by 58%. [PERSON] et al. [42] reported that a 5% amendment of BC obtained from woody material to a sewage sludge-woodchips mixture enhanced organic matter decomposition and reduced NH\({}_{3}\) emission by \(\sim\)50% during the first week of composting. [PERSON] et al. [43] achieved ammonia emission reduction of 30% and 44% by adding 5% and 10% (_w/w_) willow woodchips BC, respectively, to a poultry manure-wheat straw mixture. Research conducted by [PERSON] et al. [44] showed that a 1% BC addition to the composting mixture consisting of poultry manure and tomato stalk had a positive effect on the composting process, with improvements in physicochemical properties and microbial community diversity of the composting mixture. In the work of [PERSON] et al. [45], researchers amended a poultry litter-wheat straw composting mixture with 5% and 10% (_w/w_) of \(>\)10 mm woody BC. The addition of BC increased the temperature, shortened the thermophilic phase, and increased CO\({}_{2}\) emissions by 6.9% and 7.4%, respectively. The authors suggested that the higher CO\({}_{2}\) emissions could have resulted from the abiotic oxidation of BC or its available C that functioned as an energy source for microorganisms. The more likely scenario is that the increase in temperature promoted the microbial activity, which resulted in higher CO\({}_{2}\) emission from feedstock C digestion. It is very unlikely that C will abiotically oxidize at 70 \({}^{\circ}\)C, the higher temperature measured during the experiment. [PERSON] et al. [46] investigated green waste BC and poultry litter BC influence on the production of GHGs during composting of poultry litter-straw mixture. The cumulative emission of N\({}_{2}\)O decreased significantly by 69% and 75% after an addition to the composting mixture of 10% (by weight) of poultry litter BC and green waste BC, respectively. Total N retained at the end of the composting was 40% and 24% higher, respectively. Cumulative CH\({}_{4}\) emissions were not significantly different. However, the BC addition contributed to lower CH\({}_{4}\) emission on days 15 to 36 of the experiment that may have resulted from the porous nature of BC, which may have improved aeration and methanatrophy. Other authors [47; 48] have also confirmed the influence of BC on the composting process and microbial community of composts. [PERSON] et al. [24] added brewer's spent grain BC, in the amount ranging from 1% to 50%, to a barley, yeast, hops, and water mixture in order to increase biogas rates, and yield and rate from the anaerobic digestion of the mixture. Maximum production of biogas ranged from 61.0 to 122.0 dm\({}^{3}\)\(\cdot\)kg\({}^{-1}\)dry organic matter, with the highest amount for 5% BC addition that resulted in a 32% higher yield, compared to the control group, which coincides with results obtained by [PERSON] et al. [40]. This is yet another example of a positive way to utilize BC, as the increase in CH4 production during a controlled composting process can lead to the obtainment of a higher amount of green-energy source. Biochar amendment to the animal manure or other types of wastes subject to composting has a positive effect on the composting process (Table 3), and the positive effects are similar to the ones in the soil, in terms of reduction of greenhouse gases emission or retainment of nutrients. The similarities might apply to other areas of BC utilization. However, comprehensive studies targeting all of the emitted gases should be conducted, if feasible, because, with the reduction of some gaseous emissions, other emissions, especially CO2 and CH4, might increase.