Wood ashes: a new fertilizer for Swiss agriculture

The use of wood ashes as potash fertilizer was tested on sunflower. The greenhouse experiment was conducted in Changins and used wood ashes provided by the wood power station Enerbois (Vaud). These ashes contained high amounts of Ca and K but also trace elements, particularly Cu, Zn and Ni. Results of the trial highlighted an efficiency of K contained in these ashes equivalent to that of KCl used as reference potassic fertilizer. In NPKMglimiting conditions, the wood ashes had a positive effect on the biomass of sunflower and the absorption of K, but they reduced the amount of absorbed Ni and Zn, probably because of the negative effect of liming on the solubility of these elements. In not-NPKMg-limiting conditions, the same trends were observed regarding the biomass and the absorption of Ni and Zn. This trial showed that despite Ni and Cu contents beyond the limits currently approved in Switzerland for recycling fertilizer, it is above all the K levels that limit the amount of ashes to be spread.