Iron Characterization in Manure Amended Soils

Abstract

Materials such as sewage sludge, animal manure, humates, and compost may be rich in iron and in metal binding biochemicals that help keep iron and other metals in solution through chelation. They may also stimulate chemical and biological reactions that make iron more available. The objectives were to evaluate the effect of dairy manure applications on the different iron fractions in the soil. A differential sequential extraction method was used to determine the exchangeable, adsorbed, organic, carbonate, and sulfide or “residual” iron in the soil. Manure application had little effect on the distribution of iron or the concentration of iron in the different fractions of the soils studied. The highest percentage of iron in manure treated and nontreated soil samples was associated with the sulfide fraction (97%) followed by the carbonate fraction (1%). The exchangeable and adsorbed fractions represented less than 1% and the organic fraction between 0.001 and 0.004%. This finding may indicate low iron availability; however, the DTPA test for available iron did not show levels of deficiency. Manure application had no consistent effect on the distribution or concentration of iron in the different iron fractions of the soils tested.