Biochar and the nitrogen cycle: introduction.

Nitrogen (N) is an essential nutrient, and research to date shows that biochar potentially has the ability to manipulate the rates of N cycling in soil systems by influencing nitrification rates and adsorption of ammonia and increasing NH4+ storage by enhancing cation exchange capacity in soils. Its influence on these processes may have further implications in terms of reducing gaseous N losses such as N2O and nitrate leaching. However, further detailed research is required to fully understand the transformation mechanisms and fate of N when associated with biochar treated soils. The three research papers that comprise this special collection of papers on biochar and the nitrogen cycle focus on biochar's diverse ability to influence N cycling processes. These papers show for the first time (i) how microbial nitrification communities and function differ with exposure to biochar, (ii) how the length of time the soil has been in contact with biochar influences N transformation and how this can vary with soil type, and (iii) how composting of organic materials with biochar can reduce N losses and enhance the nutrient status of the composted product. Considerable knowledge gaps still exist in terms of understanding the precise mechanisms through which biochar influences soil N transformations, and how biochar affects both plant and microbial N supply. The general direction that research on biochar should focus on with respect to the N cycle is the effect(s) that biochar has on N transformation in soils, both chemical and biological mechanisms, and the fate of N applied to biochar treated soils. This research needs to be performed at both field plot and microbial scales.