Producing biochars for New Zealand soils

To understand the potential impacts of biochar on New Zealand soils, it is crucial to assess its capability to achieve a desired soil outcome. The present research is focused on (i) the characterization of biochars obtained from different types of feedstocks and pyrolysis conditions, (ii) the use of pre-treatments to enhance surface activity of biochars, and (iii) the simulation of long-term geochemical weathering of a mineral-rich ash biochar so that its fertilizing value can be assessed. The results obtained indicate that the different properties of the biochars produced are controlled to a large extent by process conditions (e.g., high or low temperature) and feedstock (e.g., low and high mineral ash content). Surface charge of biochars from eucalyptus and pine bark increased after treating the feedstocks with alkaline tannery waste. This effect was more evident with the biochar made from hard-wood bark. Up to 18 and 14% of K and P originally present in biochar made from biosolids were lost through intense weathering, whereas less than 1% of N was leached from the system. The knowledge acquired in this study is valuable to recognize, not only the different characteristics of the fresh biochars produced, but also their potential changes over time.