Chemical properties of soil and water-stable aggregates after sixty-seven years of cropping to spring wheat

Abstract

Three non-replicated, unfertilized, dryland grain rotations—continuous wheat, wheat-fallow, and wheat-wheat-fallow—were established in 1912 on a Dark Brown Chernozemic (Typic Haploboroll) soil. The effect of long-term cropping on the chemical constituents of total water-stable aggregates was assessed. There was a loss in percentage of total water-stable aggregates and a shift in aggregate size distribution with time. Together with an increase in the 100 μm diameter fraction, there was an increase in the sand component of this fraction. These sand particles are probably held together by alkaline-soluble, acid-insoluble organic matter. Organic carbon, polysaccharides, polyuronides, phenols, and chloroform/methanol-extractable organic matter were all associated with the >250 μm diameter fractions. Although the aggregates had generally the same suite of aliphatic carboxylic acids, the relative proportions changed with cultivation.