The effects of fulvic and humic acids on soil aggregation: a micromorphological study

SUMMARY The influence of soil amendment with fulvic + humic acid (FH) fractions, obtained from manure or peat, upon the shape, size and numerical density of aggregates in a sandy loam and a clay soil was examined using micromorphological techniques and image analysis. The effect of the FH fraction from manure (FHM) was to produce larger aggregates from the smaller ones, while the FH from peat (FHP) gave rise to a higher numerical density of smaller aggregates. Although the type of structural change was similar in the two soil types, the extent of change per g of FH was greater in the clay soil. Aggregate shape varied with treatment and soil type, but both kinds of organic matter produced vughs and a narrowing of the planes in the two soils which can be considered as signs of structural improvement.