Two Dimensional Geoelectrical Imaging of the Hardpan Layer at the Agricultural and Research Station of KFU, Al Hassa, KS

In soil science, agriculture and gardening, hardpan is a general term for a dense layer of soil, residing usually below the uppermost topsoil layer. There are different types of hardpan, all sharing the general characteristic of being a distinct soil layer that is largely impervious to water. Some hardpans are formed by deposits in the soil that fuse and bind the soil particles. Hard pans restrict root growth and make it difficult for water, air, other gases plus soil organisms to move through the soil. They are often caused by tilling or ploughing to a particular depth. The hardpan is more likely to cause severe problems if it is: closer to the surface, thicker and/or harder and particularly if it is present during a dry time or present during any other period that stresses plants. Another major determinant is the soil particle size. Clay particles are some of the smallest particles commonly found in soils. Due to their structure the spaces between individual clay particles is quite small and already restricts the passage of water, negatively impacting drainage. Soils with high clay content are also easily compacted and affected by man-made discharges. Clay particles have a strong negative electrostatic charge and will readily bond to positively charged ions dissolved in the soilwater matrix. Common salts such as sodium molecules contained in wastewater can fulfil this role and lead to a localized hardpan in some soil types. This is a common cause of septic system failure due to the prevention of proper drainage in field. Hardpan can be a problem in farming and gardening by impeding drainage of water and restricting the growth of plant roots.