Soil surface evaporation processes under mulches of different sized gravel

To reduce water loss from soil surface evaporation is important in agricultural and environmental practices, especially in arid and semi-arid regions. Gravel mulch has long been practiced to reduce soil surface evaporation. In this study, a series of simulation experiments were conducted to study the effects of gravel mulches of different sizes on evaporation process from soil surface. Four mulch treatment levels were used: diameter 0.5 cm (A), diameter 2.5 cm (B), diameter 4.5 cm (C), and bare soil (CK), with three replicates. It was found that the gravel mulches dramatically reduced the evaporation from bare soil surface, particularly when soil water contents were at high levels. Under the same soil water content, the evaporation reduction rates under gravel mulches were negatively correlated with gravel sizes. The evaporation processes under gravel mulches were much more stable as compared with that from bare soil surface. The ratio of the soil surface evaporation to the atmospheric evaporation (Ess/Esa) and soil water contents with no mulch decreased rapidly with time. Soil water contents decreased slowly with time under mulches while the Ess/Esa values maintained at the more or less stable levels. During the successive evaporation process of 41 days, the cumulative soil surface evaporation under mulches was linearly correlated with time but that from bare soil surface was logarithmically correlated with time.