Determination of Spatial Distribution of Topsoil Texture and Available Potassium Contents Using Gamma Ray Spectrometry

There are often difficulties in adequately mapping spatial distribution of soil properties at small scale due to soil variations. Gamma-ray spectrometry is a new technique that can potentially address this while improving the mapping of soil texture and available potassium (avK) and minimising huge soil survey cost and maximizing economic returns. To achieve this, secondary spatial information is incorporated into the study. Using portable Exploranium GR 320 gamma ray spectrometer, concentrations of 40K, 238U and 232Th in sandstone washed materials were measured in three plots while representative soil samples were analysed. The 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 soil texture (r2 = 0.48 to 0.67). The success of γ-ray spectrometry in predicting avK and soil texture classes 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.