Spatial Prediction of Topsoil Properties of Nong Sung Area using Gamma Ray Spectrometry

Gamma ray spectrometry tips over the conventional soil sampling method by minimising huge soil survey cost and maximizing economic returns. Relatively, it maps soil variations. Here, we look at the possibility of calibrating gamma ray concentrations to predict various surface soil properties like soil texture and available potassium (avK). The concentrations of 40K, 238U and 232Th in sandstone washed materials were measured in situ by portable Exploranium GR 320 gamma ray spectrometer while soil samples were analysed. Three plots were investigated and result showed homogeneity in on-ground γ-rays concentrations derived from γK based on the geo-lithological nature of soils. The recorded γK values and total gamma ray intensities were related to the soil texture and avK properties. Strong linear relationships were identified between γK and avK (r2 = 0.78, P < 0.001); and also with surface texture (r2 = 0.48 to 0.67). The success of γ-ray spectrometry in predicting avK and other properties relied on this strong relationship that transformed γK map into a 0.2m resolution soil property map by regression analysis, associated with 78% variance in avK and 51% clay. The overall lowest RMSE were 0.8 % clay and 1.3 mg/kg avK contents.