Physico-chemical characterization of biochars from vacuum pyrolysis of South African agricultural wastes for application as soil amendments

The physico-chemical properties of biochars from the vacuum pyrolysis of black wattle and vineyard annual prunings were investigated for their potential as soil amendments and compared to biochar from sugar cane bagasse. Biochar from sugar cane bagasse seems to be a promising sorbent and soil conditioner due to its high surface area, high surface acidity and microporous structure. This biochar can be applied to a wide pH range of soils for enhancing nutrient and water retention. On the other hand, the biochars from black wattle and vineyard possessing high concentrations of aromatic carbon, nutrients, and alkalinity are potential soil amendment agents. Black wattle biochar is more beneficial compared to biochar from vineyard due to its higher surface area, microporosity and cation exchange capacity. Therefore, this study recommends the utilization of biochars from black wattle as soil amendment agents especially in subtropical regions.

► Vacuum pyrolysis contributes to the development of CO groups on biochar's surface.
► Alkaline and acidic biochars are produced from the vacuum pyrolysis of agricultural wastes.
► Black wattle, an invasive plant, has been found suitable for soil amendment purpose.