Plant Growth Inhibition by Soluble Salts in Sewage Sludge‐Amended Mine Spoils

The growth response of prairie switchgrass ( Panicum virgatum L.) was compared in strip mine spoil amended with various levels of anaerobically digested waste‐activated sewage sludge (0, 56, 111, 222, or 333 dry Mg ha −1 ) and commercial fertilizer, pure sludge, and glasshouse soil. Plants were grown in a growth chamber and substrates were maintained at field capacity during the study. Soluble salt concentrations of the substrates increased linearly as a function of sludge amendment and were within the range known to inhibit the growth of many plant species at the high levels of sludge application. There was, however, a linear response of biomass production to increasing levels of sludge amendment. Maintaining substrates at field capacity apparently prevented the high concentration of soluble salts from inhibiting plant growth. The increased biomass yield associated with sludge application was likely due to the increased availability of inorganic nutrients associated with sludge amendment.