Biochar, Soil and Land-use Interactions That Reduce Nitrate Leaching and NO Emissions: A Meta-analysis

Biochar can reduce both nitrous oxide (NO) emissions and nitrate (NO) leaching, but refining biochar's use for estimating these types of losses remains elusive. For example, biochar properties such as ash content and labile organic compounds may induce transient effects that alter N-based losses. Thus, the aim of this meta-analysis was to assess interactions between biochar-induced effects on NO emissions and NO retention, regarding the duration of experiments as well as soil and land use properties. Data were compiled from 88 peer-reviewed publications resulting in 608 observations up to May 2016 and corresponding response ratios were used to perform a random effects meta-analysis, testing biochar's impact on cumulative NO emissions, soil NO concentrations and leaching in temperate, semi-arid, sub-tropical, and tropical climate. The overall NO emissions reduction was 38%, but NO emission reductions tended to be negligible after one year. Overall, soil NO concentrations remained unaffected while NO leaching was reduced by 13% with biochar; greater leaching reductions (>26%) occurred over longer experimental times (i.e. >30 days). Biochar had the strongest NO-emission reducing effect in paddy soils (Anthrosols) and sandy soils (Arenosols). The use of biochar reduced both NO emissions and NO leaching in arable farming and horticulture, but it did not affect these losses in grasslands and perennial crops. In conclusion, the time-dependent impact on NO emissions and NO leaching is a crucial factor that needs to be considered in order to develop and test resilient and sustainable biochar-based N loss mitigation strategies. Our results provide a valuable starting point for future biochar-based N loss mitigation studies.