Mikko Moilanen

Release of mineral nutrients and heavy metals from wood and peat ash fertilizers: Field studies in Finnish forest soils

Two field trials were conducted to study the rate of release of nutrients and heavy metals from wood and peat ash fertilizers in forest soils. In the first experiment, ash particle residues were extracted from peat and mineral soils 3 and 5 years after spreading and analysed for changes in element concentrations. Dissolution of different ash fertilizer products was also estimated by measuring the changes over time in the recovery of added nutrients and heavy metals in the surface of two peat soils. The results showed that potassium (K), sodium (Na), boron and sulfur are easily released from wood ash, whereas heavy metals are highly insoluble in all types of ash fertilizer products. Granulated ash fertilizers were less soluble than powdered fertilizers and the products stabilized by self-hardening. Minor differences occurred in ash fertilizer dissolution between peat and mineral soils and soils of different fertility. The most significant difference between wood and peat ash concerning their dissolution was the low solubility of K and Na in peat ash. Given the very slow dissolution of ash fertilizers, long-term studies are needed to understand fully the effect of ash fertilization on nutrient and heavy metal cycling in forest ecosystems.

Effects of wood bark ash on the growth and nutrition of a Scots pine afforestation in central Finland

Results are presented from a fertilization experiment with wood bark ash (0, 1, 2, 5, 10, 20 Mg ha-1) applied to prevent and cure visible nutrient disorders of young Scots pine established on a peatland field. 13 years after fertilization, dieback of trees and other symptoms of nutrient disorders were substantially reduced or even eliminated, especially where higher doses had been applied. The volume of the growing stock was more than 70 m3 ha-1 for the highest dose while control plots produced less than 15 m3 ha-1. Vegetation characteristics changed following ash treatments with high ash doses favouring grasses and low ash doses promoting mosses. Some major changes in soil and foliar nutrient concentrations were evident due to ash fertilization. K and B, however, were clearly the most limiting nutrients that could be cycled where high doses of ash were used. This was particularly the case with a dose of 20 Mg ha-1. Decomposition of the topsoil was at its highest on plots with ash doses of 5 and 10 Mg ha-1 ash and at its lowest when the dose was 2 Mg ha-1. This was partly due to differences in the C/N ratio of the soil. All decomposition parameters indicated a high degree of humification in the topsoil. High N content (of organic material), low C/N in the soil and optimum levels of foliar N concentrations suggested sufficient N mineralization for tree growth to have occurred in the soil.

Uptake of 137Cs by berries, mushrooms and needles of Scots pine in peatland forests after wood ash application

Increasing use of wood fuels for energy production in Finland since the 1990s implies that large quantities of the generated ashes will be available for forest fertilization. The aim of this study was to analyse the effect of wood ash application on ¹³⁷Cs activity concentrations in Scots pine (Pinus sylvestris L.) needles and certain berries and mushrooms on drained peatlands. The study was based on field experiments carried out on two mires in Finland in 1997-1998. Two different types of wood ash were applied at dosages of 3500, 3700, 10 500 and 11 100 kg ha⁻¹. Wood ash did not increase ¹³⁷Cs activity concentration in plants in the second growing season following application. On the contrary, a decrease in ¹³⁷Cs activity concentration was seen in the plants of the ecosystem on drained peatlands. This result is of importance, for instance, when recycling of ash is being planned.