Agronomic potential of ash from recycled wood

The effect of wood ash as a potash fertiliser was tested on perennial ryegrass in a greenhouse. The ash, which was from recycled wood, was spread – in some cases in combination with organic fertilisers – on two types of soil: an acid soil low in available potassium, and an alkaline soil with normal supplies of potassium. The ash studied was rich in calcium and potassium. It also contained high levels of microelements and trace metals such as zinc, copper and lead – levels which might exceed thresholds currently authorised in Switzerland. Compared to another type of previously tested ash, the ash in this study contained more trace metals, and the potassium therein was less available. The ash enabled the production of ryegrass biomass equivalent to that of the reference fertiliser (KCl) on an acid soil. The use of ash on an alkaline soil with normal supplies of available potassium appears to be less appropriate. The results obtained in this test show the importance of the quality of the ash used, which depends on the origin of the wood (natural or recycled) and on the combustion process.