The role of rock fragments in evaporation from cultivated soils under mediterranean climatic conditions

Abstract

A large proportion of the soils in the Mediterranean contains considerable amounts of rock fragments (i.e. mineral particles larger than 2 mm). In contrast to the reduction of evaporation depth by a continuous gravel mulch, the effects of rock fragments within the soil profile and at the soil surface is largely unknown. This paper presents the results of laboratory experiments where evaporation rate from soils containing a range of rock fragment contents is compared to a non-stony control soil and a non-stony soil covered with a rock fragment mulch. Evaporative demand (E o) during the experiments varied between 7.7–9.2 mm day −1. Two contrasting conditions frequently found in the Mediterranean were tested: soils at field capacity (beginning of the growing season) and air-dry soils that received only 10 mm of rain (end of the growing season). The lower evaporation depth from stony soils is most evident in the initial phase (constant rate stage) when the soil is wet. During this stage rock fragments act as a partial mulch. However, when a limited amount of rain falls on an air-dry soil, the constant rate stage is absent and the falling rate stage dominates water losses. During this phase, dry stony soils loose their water more quickly, probably due to a concentration of soil moisture in the fine earth.