The Influence of Mount St. Helens Ash on Wheat Growth and Phosphorus, Sulfur, Calcium, and Magnesium Uptake

Concern has been expressed that large amounts of volcanic ash from the 18 May 1980 eruption of Mount St. Helens may have created potential nutrition problems associated with wheat (Triticum aestivum L.) production in eastern Washington and northern Idaho to the extent that adjustments need to be made in soil test correlation data. The objectives of this study were to: (i) determine the effect of varying amounts of volcanic ash, either mixed into or placed on the surface of eight different agronomic soils of northern Idaho on total biomass production of wheat under greenhouse conditions, and (ii) to determine the effect of various soil-ash mixtures on the nutrient concentration and total uptake of P, S, Ca, and Mg by wheat. Wheat was grown in eight different northern Idaho soils amended with differing levels of volcanic ash (0, 20, 35, 50, and 75%) in the greenhouse. Fertilizer N, P, and S were added to all treatments. Total plant biomass and P, S, Ca, and Mg concentrations and uptake were measured. Increasing amounts of volcanic ash gave no consistent effects on total wheat biomass. Based on biomass yields, soils were placed into four basic categories: (i) those where increasing levels of ash depressed plant growth, (ii) those where increasing ash levels stimulated biomass production, (iii) those where biomass yields were greatest with moderate levels of ash, and (iv) those where biomass yields were mixed. Plant S and P concentrations increased with increasing levels of ash for most soils. The ash did not fix appreciable amounts of P and increased plant-available S. The ash also enhanced Ca and Mg uptake by plants. There is no evidence to suggest that high levels of ash (700 000 kg/ha) inhibit wheat biomass production. Consequently, there is no need for adjustments in soil test calibration data presently used for fertilizer recommendations for wheat.