Different strategies have been tested to reduce nitrogen losses and gaseous ammonia emissions during composting. Among them, the supplementation of the composting mixture with biochar has shown good results and has attracted increasing attention from researchers over more than a decade. In order to capitalise on the numerous existing results, the relevant data from the literature were subjected to descriptive statistics and to a Pearson parametric correlation analysis. The statistical treatment of the literature data confirms that biochar reduces nitrogen losses, ammonia and nitrous oxide emissions during composting with highly variable performance (respectively reduction of 26.2% +/- 16.7%; 46% +/- 26.4%; 46.1% +/- 31.1%). Statistically significant correlations were identified between N losses and biochar properties. However, the PCA results show that only 44.75% of the variability in the N loss reduction dataset and 57.8% of the ammonia emission reduction dataset were explained by the main variables available in the literature. This suggests that much of the variability in biochar performance remains unexplained. The large number of variables involved in the process and the lack of fine characterisation of biochar in most studies explain the remaining difficulty in fully understanding the complex action of biochar in composting and opens up prospects for further research.