Changes in physico-chemical and biochemical parameters of soil following addition of wood ash: a field experiment

Here we have investigated the effects of the addition of two different wood ash sizes at two different doses (5 and 20 t/ha) on the physicochemical, microbiological and biochemical properties in the surface soil (0–30 cm) of an Italian agricultural system. Over 24 months, the pH, electrical conductivity, soil microbial biomass-C and -N, and total hydrolytic activity were periodically tested, together with alkaline phosphatase, arylsulphatase and o-diphenoloxidase activities. Analysis of variance (ANOVA) was performed to consider the effects of sampling time and wood ash addition on the parameters tested and to reveal possible interactions between the two variables. For electrical conductivity, pH, soil microbial biomass-C and total hydrolytic activity the ANOVA showed a significant ‘wood ash type× sampling time’ interaction, while no interaction was found for the other enzymatic activities. Significant increases in pH and in electrical conductivity were seen over the first months in all of the treated samples, which were more pronounced at the higher dose. Decreases in microbial biomass-C and changes in the microbial C/N ratios were seen for all of the treatments, which were more pronounced at the higher dose. Increases in soil microbial activity were seen over the first 8 months. The alkaline phosphatase and arylsulphatase activities were significantly inhibited for the first 4 months of soil treatment. The significant increases seen in o-diphenoloxidase activity over the first 8 months under all of the treatments appear to be related to the increases in electrical conductivity. After 12 months, the levels of all of the parameters tested in the treated soils returned to the levels of the untreated soils indicating that the disposal of up to 20 t/ha of wood ash per year in Italian agricultural soil does not result in long-term changes in any of these parameters.