Ameliorating acid soils with organic materials: effects of amendments derived from coal on yield and composition of young wheat plants grown on an acid red podzol

Abstract

Acidity in surface and subsurface soil horizons limits crop and pasture production over considerable areas of the world, and lime is the traditional amendment used to neutralize surface soil acidity. Earlier reports have indicated that calcium (Ca)‐saturated organic materials, produced by the oxidation of coal, may be of value as ameliorants for subsurface acidity. Two of them (OXPR and OXFU) were evaluated and compared with lime in pot studies with wheat (Triticum aestivum). In the first experiment, lime, OXPR and OXFU, each at four rates, were applied to an acid red podzolic soil, high in extractable aluminum (Al) and were compared for their ability to improve seedling root growth. In the second experiment, the three amendments were applied to the same soil and shoot yields and mineral content were measured after five weeks growth. The three amendments raised soil pH, lowered extractable Al and increased root elongation. OXFU at the highest rate (251 ha‐1) inhibited root growth possibly due to the high concentration of solutes as indicated by high electrical conductivity of the soil solution. In the second experiment the three amendments improved shoot yields, with significant increases up to 0.81 Ca ha‐1 application. Yields were in general higher with lime than with OXPR and OXFU at equivalent rates of added Ca. However, a significant asymptotic relationship was observed between yield and calcium carbonate (CaCO3) equivalence of each of the applied amendments. Yield was highly correlated with measures of soil Al {r2 for [Al] in 0.01M calcium chloride (CaCl2), 0.915; [Al] in 0.1M barium chloride (BaCl2)/ammonium chloride (NH4C1), 0.873; [Al] in water, 0.779; [Al] in water/EC, 0.904}. Plant manganese (Mn) concentrations were decreased by lime and OXPR and there were linear correlations between plant Mn concentration and soil Mn extractable in 0.01 M CaCl2 With OXFU, which has a high concentration of water soluble Mn, plant Mn was decreased below the unamended controls only at the higher rates of application. .Leaf tissue zinc (Zn) concentrations were high in treatments receiving the two coal‐derived amendments. In an effort to determine the role of ion complexation in the remediation process, a third study evaluating the Al complexing ability of the two coal derived products was compared to that of a water‐soluble fraction extracted from chestnut (Castanea saliva) litter which is known to have a high affinity for Al. The two coal derived materials had considerably lower affinities for Al than the chestnut extract supporting the thesis that complexing reactions were of minor importance in the observed responses. The results indicate that field testing of these products is warranted particularly at sites where plant growth is constrained by subsurface soil acidity.