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Repeated electromagnetic induction (EMI) surveys have merits of revealing temporal changes in heterogeneous soilscapes such as subsurface hydrologic dynamics. We conducted eight repeated EMI surveys from 1997 to 2009 over a 19.5-ha agricultural field that revealed soil and water patterns. The first two surveys were done in 1997 and 2006 and compared different EMI meters (EM38, EM31, and Dualem-2), dipole orientations, and geometries. Another six surveys were conducted in different seasons in 2008 to 2009 using the EM38 operated in vertical dipole orientation. Soil apparent electrical conductivity (ECa) collected during the wetter periods (>10-mm antecedent precipitation during the previous 7 d) showed greater spatial variability (greater sills and shorter spatial correlation lengths), indicating the influence of soil water distribution on soil ECa. During a relatively short time period, most soil properties controlling ECa (e.g., texture, organic matter, and depth to bedrock) remain unchanged. Thus, repeated EMI surveys can capture the dynamics of soil moisture change and related subsurface flow paths in the landscape. Significantly (p < 0.05) higher ECa was detected in areas dose to simulated subsurface flow paths, especially during the wetter periods; however, such flow paths could not be pinpointed directly from the ECa maps because of the limitation in ECa spatial resolution. In wetter areas, significant correlation between the relative difference in ECa and that in measured soil moisture was observed ([r.sup.2] = 0.59-0.77), but not in drier areas. During drier periods or at drier locations, the influences of soil moisture and flow path on ECa were masked by terrain and other soil properties. Thus, the optimal use of EMI for detecting subsurface hydrologic dynamics would be during wet periods or in wet areas across the landscape in this study. doi: 10.2136/sssaj2010.0055

Soil apparent electrical conductivity (ECa) measured by electromagnetic induction (EMI) has been widely used to interpret soil spatial variability. We investigated the use of repeated EMI surveys, in combination with depth to bedrock and terrain attributes, to improve soil mapping in a 19.5-ha agricultural landscape. The first two surveys were done in 1997 and 2006, in which different meters (EM38, EM31, and Dualem-2), dipole orientations, and geometries were compared. The EM38 operated in vertical dipole orientation was then used in another six surveys in different seasons from 2008 to 2009. Results showed that the optimal use of EMI depends on the targeted soil properties, landscape characteristics, specific EMI meter and its setting, and the timing of the survey. The EM31 operated in vertical dipole orientation provided the deepest measurement depth (6 m) among the three meters used and showed the strongest relationship with depth to bedrock in the study area ([r.sup.2] = 0.58). Because the top 2 m of soil profiles exhibited distinct textural differences across the landscape, the EM31 operated in horizontal dipole orientation and Dualem-2 operated in horizontal co-planar geometry (both with 3-m measurement depth) showed the best correlation with silt content ([r.sup.2] = 0.45-0.47). The best EMI mapping of major soil distribution across this landscape requires optimal timing (wet period) and an appropriate meter and setting. No single EMI survey or the relative difference in ECa of repeated EMI surveys was sufficient to obtain the best possible soil map for the study area. Instead, a combination of repeated EMI surveys, depth to bedrock, and terrain attributes provided the best mapping of soils in this agricultural landscape and doubled the accuracy of map unit purity compared with the existing second-order soil map. doi: 10.2136/sssaj2010.0056

Early alterations which take place when the main material used for minesoil construction consist of unoxidized overburden containing acid-forming materials and extra acid neutralizing potential. Lysimeters are filled with fresh, pyritic overburden which have a positive acid-base account, and deionized rainwater is used to leach it monthly. Gypsum crystals settle in vughs, channels and in purite crystal margins in the bottom portion of the lysimeters. Gypsic or petrogypsic horizon is caused by sustained gypsum precipitation. Vertical transport of water and O2 which lower vegetative development, enhanced runoff, erosion and loss of reclamation will be lowered by such preventive layers.