Relationship between the decreases in soil stability effected by the growth of maize roots and changes in organically bound iron and aluminium

The growth of maize roots decreased fresh soil aggregate stability. Chemical pretreatment with sodium periodate (to assess the importance of polysaccharides) and acetylacetone (to assess the importance of organically bound Fe and Al) before measuring stability suggested that destruction of (organic matter)-(Fe or Al)-(mineral particle) linkages largely accounts for the effect. Removal of the Fe and Al cations by chelating agents released in the rhizosphere is the most likely mechanism. Changes in soil particle size distribution and the concentrations of water-extractable cations around maize roots did not appear to be implicated. Concentrations of water-extractable Mg and K were sometimes greater in fresh soil which had supported maize than in fallow controls, which may reflect both release of bicarbonate or organic anions by the roots and the slaking of aggregates, reducing stability of the fresh maize soils.