Exogenous humic substances as conditioners for the rehabilitation of degraded soils

Rapid loss of humified soil organic mailer (SOM) from erosion, frequent use of heavy machinery and/or over-exploitation is causing accelerated degradation of agricultural lands in arid, semi-arid and tropical climates, Soil application of exogenous humic substances such as coal-derived humic acids (HA) may help io counteract this problem. Through series of laboratory studies which utilized typically degraded Mediterranean soils from Italy, ii has been shown that amending problem soils with such HA can increase the amount of available water stored in the crop root zone, thereby reducing the amount of irrigation water needed to sustain crop productivity in arid climates. HA were able to enhance the water-stability of aggregates and moderate the adverse effects of cyclic wetting and drying on soil structure Substantial improvements in these properties were obtained at relatively low rates of HA (100 to 200 Kg/ha), Rainfall simulator experiments have shown that application to soils of HA as low as 100 to 200 Ka/ha can reduce soil erosion of sandy soils by as much as 40%. The acting modes by which the HA improved soil physical properties are attributed to both the high content of hydrophilic and hydrophobic components of this coal-derived HA. While the hydrophilicity of complexation of the polyvalent cations in the clay surfaces with the HA oxygen-containing groups orients the hydrophobic components around the soil aggregate. Such hydrophobic coating reduces soil slaking in water thereby maintaining aggregate stability and preventing soil loss by run-off erosion. These results highlight the great importance that a potentially economically viable material such as coal-derived humic substances can have in the reclamation and conservation of physically degraded soils.