MICROBIAL ACTIVITY AND LONG-CHAIN ALIPHATICS IN THE FORMATION OF STABLE SOIL AGGREGATES

Under intensive farming, restoration of organic matter levels and soil structure may depend on the amount and nature of the organic amendment added. The effect of three types of aliphatic compounds on the water aggregate stability of a chemically altered lacustrine heavy clay was studied in a 35-d incubation experiment. Water-stable aggregates were determined before and after unbound lipids were extracted. The addition of ethyl ether insoluble aliphatic produced 0 to 50 mg C kg-1 as CO2 and increased water-stable aggregates by 7 to 17.5%. The acid and neutral fractions produced 0.32 to 12.93 g C kg-1 as CO2, and resulted in acceptable aggregate stability. Stability may be attributed to the binding of aliphatic compounds to the inorganic component through polyvalent cation bridges. High correlation coefficients (P less-than-or-equal-to 0.001) for the acid and neutral fractions were found between the amounts of aliphatic compounds added, bound organic compounds extracted, CO2 evolved, and water-stable aggregate stability. The increase in soil aggregate stability appears closely related to bound aliphatic compounds incorporated into the aggregates as a result of microbial activity, and that the effect of aliphatic compounds on soil aggregate stability is associated with both their quantity and chemical nature.