Biochar: an improver of nutrient and soil water availability - what is the evidence?
2014
Scott, H. L. | Ponsonby, D. | Atkinson, C. J.
Biochar has consistently been proposed for improving soil fertility by increasing nutrient and soil water availability. We critically reviewed the recent literature, focussing particularly on these agronomic aspects. We clarify the differences between biochar made from plant (plant-derived biochar, PDB) and animal feedstock (animal-derived biochar, ADB) and show how the pyrolysis temperature affects biochar properties. We also tabulate crop yield data against production variables using recent field and greenhouse studies. We found evidence to suggest that ADB supplies many more nutrients than PDB and that, in general, biochar can improve nutrient availability indirectly through changes in pH, CEC, soil structure, improved fertilizer efficiency, decreased nutrient leaching and may affect nutrient availability by changing nitrogenous gas release and the soil microbial community, which, under some circumstances translates into short-term, increased crop yield. Few studies however show complete nutrient budgets particularly for N and do not elaborate on the underlying mechanisms of interaction, especially with regards to microbial-induced changes. Also the longevity of the different beneficial effects is questionable as most studies are less than a year long. A synopsis of the literature concludes that biochar application promotes soil water-holding capacity, particularly in soils that are degraded or of low quality. Despite this conclusion, it is hard to find studies that have adopted methodologies which are fully appropriate to support an increase in available water, such as available water capacity and how this changes in response to crop uptake and soil drying. We conclude that the variability in biochar, due to the variable feedstock and pyrolysis process, as well as particle size and application method necessitates and also enables production of specific purpose-driven biochars to benefit particular aspects of crop production.
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