AGRICULTURAL GEOPHYSICAL IMPLICATIONS AT THE AGRICULTURAL AND RESEARCH STATION OF KFU, AL HASSA, KSA

The agricultural and research station of King Faisal University, KSA is a key field of scientific studies conducted by faculty members and graduates. Soil salinity and the existence of a hardpan layer are considered to be dominant problems, which affect the agricultural activities in this agricultural research station. Electromagnetic induction & electrical resistivity tomography implemented in this study to contribute to these problems. The EM38-MK2 conductivity meter, is inexpensive, rapid and effective means for the mapping of soil salinity. The EM38-MK2, when used in vertical mode can measure the electrical conductivity (EC) at depths of 75 and 150 cm at about 700 sites along the study area. About 157 soil samples using the hand auger were collected at depth intervals of 10-20 cm and 3040 cm for the same site. The electrical conductivity for the collected soil samples were measured at the lab to correlate with the EM38-Mk2 data. In addition, 2-D electrical tomography using SuperSting R8/IP 8 channel multi-electrode resistivity and IP imaging system with 112 electrodes at 3 meter spacing implemented along selected profiles were used to map the hardpan layer. Soil pits were excavated to help with the interpretation of the resistivity tomograms and to know the nature of such layer. The collected EC using the data of the EM38-MK2 were processed & analyzed and two salinity maps constructed at 75 & 15cm. In addition, two salinity maps were constructed from the EC data of the collected soil samples at depth intervals of 10-20 cm and 30-40 cm. Both salinity maps of EM38 correlate well with the salinity maps of lab measurements. The salinity variation was found to change laterally and vertically due to changes in soil type/texture and soil moisture. Analysis and interpretation of the 2-D resistively data along with soil pits provided information on the geometry of the hardpan in this area of study. This hardpan layer is a shale layer with low resistivity zone on 2-D tomograms. The existence of the hardpan layer at shallow depths was found to have its impact of high salinity areas.