The effects of ‘Colas’ bitumen emulsion on soil temperature, soil moisture and the stability of soil structure were determined in temperate and tropical conditions.
At a depth of 5 cm, soil temperature increments of from 2°c in England to 8°c in Trinidad were recorded when the soil was mulched with bitumen. Temperatures under bitumen were shown to be higher than those under mulches of black polyethylene, sand or pine needles, and in unmulched soil. It was also shown that growing crops exerted an increasing shading effect which limited the period of effectiveness of a mulch. When the mulch is applied in bands, these should be at least 15 cm wide for maximum temperature increments to occur.
Soil moisture studies were conducted both in the field and under laboratory/glasshouse conditions. It was found that only comparatively thick mulches on smooth soil surfaces, caused any appreciable reduction in water losses through evaporation.
It was found that the crumb structures of soils treated with very thin bitumen mulches (∼150μ thick) were able to withstand considerably more weathering by rainfall or irrigation than unmulched soil before breakdown of the soil surface structure occurred.