Alex Demeyer

Characteristics of wood ash and influence on soil properties and nutrient uptake: an overview

Wood industries and power plants generate enormous quantities of wood ash. Disposal in landfills has been for long a common method for removal. New regulations for conserving the environment have raised the costs of landfill disposal and added to the difficulties for acquiring new sites for disposal. Over a few decades a number of studies have been carried out on the utilization of wood ashes in agriculture and forestry as an alternative method for disposal. Because of their properties and their influence on soil chemistry the utilization of wood ashes is particularly suited for the fertility management of tropical acid soils and forest soils. This review principally focuses on ash from the wood industry and power plants and considers its physical, chemical and mineralogical characteristics, its effect on soil properties, on the availability of nutrient elements and on the growth and chemical composition of crops and trees, as well as its impact on the environment.

Chemical effects of wood ash on plant growth in tropical acid soils

Abstract A greenhouse study was conducted to compare chemical effects of wood ash and CaCO3 on the growth of rye grass (Lolium perenne L.) in three tropical acid soils (Kandiudult). Amendments were applied at rates to attain target pH values of 5.5, 6.0 and 6.5. Generally, plants grown on ash-amended soils showed higher biomass production than did plants grown on lime and control treatments. After wood ash application, plants benefited from Ca and K supplementation, the synergy K-NO−3 and from changes in soil chemistry similar to lime application: higher ECEC and reduced Al and Mn toxicity. Therefore, wood ash appeared at the same time as a neutralizer of soil acidity and as a supplier of nutrients for tropical acid soils.

Effect of wood ash application on soil solution chemistry of tropical acid soils: incubation study

The objective of this study was to determine the effect of wood ash application on soil solution composition of three tropical acid soils. Calcium carbonate was used as a reference amendment. Amended soils and control were incubated for 60 days. To assess soluble nutrients, saturation extracts were analysed at 15 days intervals. Wood ash application affects the soil solution chemistry in two ways, as a liming agent and as a supplier of nutrients. As a liming agent, wood ash application induced increases in soil solution pH, Ca, Mg, inorganic C, SO4 and DOC. As a supplier of elements, the increase in the soil solution pH was partly due to ligand exchange between wood ash SO4 and OH- ions. Large increases in concentrations of inorganic C, SO4, Ca and Mg with wood ash relative to lime and especially increases in K reflected the supply of these elements by wood ash. Wood ash application could represent increased availability of nutrients for the plant. However, large concentrations of basic cations, SO4 and NO3 obtained with higher application rates could be a concern because of potential solute transport to surface waters and groundwater. Wood ash must be applied at reasonable rates to avoid any risk for the environment.

Availability of Nutrients in Wood Ash Amended Tropical Acid Soils

A greenhouse study was conducted to assess nutrient availability in wood ash when applied to surface soil samples of three tropical acid soils (Kandiudult) from Cameroon. Amendments were applied at rates to attain target pH values of 5.5, 6.0 and 6.5. Lime treatments were included as a control. Rye grass (Lolium perenne L.) was grown as an indicator plant for three successive cycles of 40 days each. Data on total harvested dry matter, nutrient uptake, nutrient additions and extractable soil nutrients from treated soils have been used for availability investigations. Application of wood ash resulted in neutralisation of soil acidity, increased exchangeable nutrient bases and decreased extractable micronutrients. Wood ash was in general more effective than lime in increasing dry matter production, mainly because of higher P and K uptake. Phosphorus, Ca, Mg, K, Mn, Zn and Cu from wood ash were used by plants. Wood ash application increased the availability of P, Ca, Mg and K and decreased that of Mn and Zn f...