Importance of subsurface soil pockets for plant growth in a karst environment

摘要

Northern Yucatan has generally shallow soils (< 30 cm depth) underlain by limestone, and an aquifer at several meters depth. Pockets of soil have accumulated within the limestone bedrock as a consequence of rock dissolution and illuviation of finer materials from topsoil. These soil pockets are thought to be additional sources of water and nutrients for plants but their abundance and properties have been poorly studied. This study was conducted in a limestone quarry, where the aquifer is at 9 m, to determine the abundance and distribution of soil pockets and to compare their physical properties with those of the topsoil. Soil pockets represented about 12 % of area of the vadose zone, whereas topsoil occupies only 3.3%. The volume of the soil contained in soil pockets was twice as much as the volume occupied by topsoil. Deeper and finer roots were regularly associated with soil pockets. Soil pockets had 3 times more clay and 10% less porosity compared with topsoil. Available water was similar in topsoil and soil pockets because field capacity and permanent wilting points were higher in soil pockets. Soil pockets are more abundant than previously thought and have different properties than topsoil.