Soil aggregate stability and organic matter in clay and fine silt fractions in urban refuse-amended semiarid soils

Organic refuse application to soil may improve soil structure and thus soil quality and productivity. Two semiarid, structureless soils with < 10 g kg(-1) organic C (OC), differing in clay mineralogy, were amended annually at rates of 30 g kg(-1) fresh or composted refuse to a total of 60 g kg(-1) in a greenhouse experiment lasting 2 yr. Fresh refuse additions significantly increased the soil aggregate stability in water by 17%. Composted refuse application only increased aggregate stability in the beidellitic clay-dominated soil (13%). In both soils, the greatest increase in OC and humin following refuse additions occurred in the fine silt fraction, which contained less decomposed organic matter than the clay fraction. In the beidellitic clay soil, this increase in OC was larger than in the illitic clay soil. The aggregate stability of the beidellitic clay soil was significantly correlated with OC and humin of fine silt fraction.