Response of Pinus radiata seedlings to application of mixed wood-bark ash at planting in a temperate region: Nutrition and growth

The aim of the present study was to evaluate the initial effects of the application of mixed wood-bark ash (MWBA) on growth and nutritional status of a Pinus radiata plantation, and on the dynamics of some of the nutrients. A field experiment, which included four treatments and four replicates in a completely random design, was established on an acidic, mineral soil rich in organic matter. The treatments were two different doses of ash (5 and 10tha⁻¹), a soluble NPK fertilizer 8:24:16 (N:P₂O₅:K₂O, 200g per plant) and an unfertilized control. The MWBA was incorporated into the soil after cutting and chopping the existing shrub vegetation and before planting. Application of the ash produced an increase in soil pH, and in the availability of P, Ca, Mg and K. The effects on soil pH and available Ca and Mg persisted for five growing seasons. The prolonged response in this study may be attributable to the effect of ash incorporation, which may have enhanced the solubility of wood ash compounds, despite the partly combusted material present in the ash. The ash improved the nutritional status, mainly in terms of Ca and Mg, and the vector analysis indicated that these elements were limiting forest production. The soluble NPK fertilizer did not produce any improvement in growth relative to the control. The concentrations of heavy metals in both soil and plant tissue were always low and did not increase significantly after application of the wood-bark ash. The positive effect of ash application on height and diameter growth was significant after 5 years, with similar results for both doses of ash. The improvement was attributed to the increases in Ca and Mg in soil. The differences between the treatments with ash and the control were much greater when the values of biomass per unit area were considered, due to the accumulative effect of a lower mortality and the enhanced growth in basal diameter and height.