WOOD ASH AS A LIMING AMENDMENT

Greenhouse and laboratory experiments were carried out to determine the effectiveness of a wood-derived ash as a lime replacement. Treatments included wood ash, wood ash and lime admixtures, and lime amendments (ash amendment ranged from 0 to 20.17 and lime amendment from 0 to 4.06 g/kg soil on a dry weight basis). Treatments were compared for influence on soil pH, capacity to supply mineral nutrients to spinach (Spinacia oleracea L. 'America'), and for effects on soil nutrient retention, leaching and electrical conductivity (EC). Plant dry weight did not differ within lime alone or wood ash alone treatments. However, in admixtures of the two, plant dry weight increased with increasing rate of wood ash addition. Wood ash containing amendments had a greater positive effect on soil pH than did lime only treatments. Wood ash treatments increased soil EC, while lime only treatments had no effect. Losses of mineral elements decreased with successive leachings for treated and control soils. Calcium, K, and Na were leached from the soil in greater amounts from wood-ash treated soil. Leached Mg, however, was attributed to the soil and not to the amendment. Soil K and Ca at harvest increased linearly with increasing wood-ash rate, whereas Mg decreased linearly with decreasing lime rate. Extractable soil P, Fe, Zn, Cu, and Mn increased with wood ash amendment. Soil Al decreased linearly with wood ash amendment in the wood ash-lime admixtures. Plant Mg uptake was proportional to extractable soil Mg content. Plant K followed the same trend but reached a maximum at 150 mg/kg plant dry weight. Mn and P increased linearly as wood ash amendment increased. Plant Al, Cu, Fe, and Zn increased only in the wood ash-lime admixtures. The results of this study suggest that wood ash might be more appropriately used as a liming complement rather than as a replacement.