Influence of olive mills solid waste on soil hydraulic properties

The annual production of olive fruits in Jordan is about 105,000 tons producing more than 80,000 tons of solid waste annually. Olive mills solid waste (OMW) contains 94% organic matter and, therefore, can be highly beneficial to agricultural soil. However, olive waste contains oil that may increase soil hydrophobicity and decrease water retention and infiltration rate. In this research, the impact of OMW on water retention, saturated and unsaturated hydraulic conductivity, and capillary rise of three soils, loam, clay loam, and dune sand, has been investigated under laboratory conditions. Application of OMW resulted in an increase in water retention and saturated hydraulic conductivity but caused a decrease in capillary rise and unsaturated hydraulic conductivity for all soils tested. The increase in water retention has been observed at all levels of pressure potential and was significantly different at 3 bars or higher. The highest increase in saturated hydraulic conductivity occurred at 4% application rate at which about 300%, 200%, and only 12% increase was observed for loam, clay loam, and dune sand, respectively. Application of OMW caused a significant decrease in the capillary rise ranging from 11.5% for dune sand to 70% for clay loam soil. Capillary rises were inversely related to the OMW treatment level for all soils tested.