Desorptivity: an index of soil drying
1996
Mensah, Bonsu (University of Cape Coast (Ghana). Dept. of Soil Science)
Desorptivity evaluation was carried out using ten soils with different textures from different locations in Ghana, evaporation was effected in direct sunshine during the day and with a fan in the laboratory during the night. The study was carried out in dry harmattan winds during the day. From the cumulative evaporation (E) and time (t) and time (t) curves, it was deduced that evaporation in dry harmattan winds behaved as in an environment with constant evaporativity. The falling rate stage of evaporation began after 5 days of continuous evaporation. During the falling rate stage, E was observed to be proportional to t 0.5, as predicted by theory. The desorptivity (Sd) calculated during the falling rate stage of evaporation was observed to increase exponentially with water content of the soil during the falling rate stage and a negative correlation with percent sand and a positive correlation with percent clay. Both correlations were not statistically significant. Evaporation tended to increase with sand content during the initial state when water was not limiting. Under water limiting case, evaporation tended to increase with clay content. The increase in evaporation loss with clay content during the water limiting case may be explained to be due to the effect of capillarity in clay soils. In areas with limited water supply, it is helpful to shallow plough the soil frequently to break the continuity in capillary pores of clay soils in order to conserve water below for crop use
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