Production and physico-chemical properties of surface casts from microchaetid earthworms in central Eastern Cape

Abstract

The study was undertaken to estimate surface cast production by microchaetid earthworms and to compare the physical and chemical properties of the casts with the surrounding non-cast soil. An average of 104 (range 64–132) and 192 (range 182–222) t ha⁻¹ of surface casts were produced at Alice and Dimbaza sites in central Eastern Cape during the period September 1995 to August 1996. The casts had an average height of 6.8 cm and diameter of 5.6 cm and had higher silt and clay (66.2 vs 62.9%) but lower sand (33.8 vs 37.1 %) sized partides than the non-cast surface soil. The casts also had a higher proportion of water stable aggregates > 0.5 mm (76.7 vs 67.2%), mean weight diameter, bulk density (1.55 vs 1.37 Mg m⁻³) and retained more water than the non-cast soil. Earthworm casts had significantly higher available Bray 1-P, exchangeable K, Ca, Mg and Na than the non-cast soil. Levels of organic C and pH were also elevated in earthworm casting compared to surrounding soil. The large amounts of casts that are deposited on the surface can play an important role in modifying the hydraulic properties at the soil surface and help minimise runoff and erosion. Because of the high concentration of nutrients in casts compared to non-cast soil, potential may exist for using the casts to supply plants with nutrients.