Abstract

The effect of the addition of urban refuse (UR) on the percentage of stable aggregates in a semi-arid structureless soil was studied in a 67-day incubation experiment. Twelve systems were established combining amendments with two doses of UR (2.4 and 4.8%) and treatments with cycloheximide, chloramphenicol or formaldehyde to evaluate the relative efficiency of carbohydrates and microbial (fungi and bacteria) communities in promoting changes in aggregate stability. The addition of UR to the soil increased the abundance of stable aggregates and this increase was proportional to the quantity of UR added. The degree of aggregate stability was related to all the factors considered, although this relationship was more evident for the fungal communities (R = 0.81, P < 0.001) and, to a lesser extent, for the bacterial communities and carbohydrate content. Carbohydrates were significantly correlated with stable aggregates during the first stages of incubation (R = 0.83 P < 0.001, at day 4), but this effect was short-lived and the maintenance and increase of the aggregate stability in the subsequent phases was attributable to the increases in microbial populations, and particularly to the proliferation of fungal mycelium.