Hyperspectroscopic and microtopographic analyses of salt crust forms on arid, silty clay loam desert soils

This paper describes simultaneous uses of field sampling and hyperspectroscopic approaches to understand the distributions of salt crusts and factors affecting them under field conditions. Samples of salt affected soils and associated salt crusts that represented a range of soil salinities, slope, and moisture contents were gathered from the banks of the Rio Grande. The samples were studied for salt identification by optical microscopy and using a high-resolution spectroradiometer, GER 3700, and for salinity level, and moisture content by the wet chemistry method. The study identified two main groups of salt crusts, contaminated halite and gypsum crusts. Reflectivity was correlated negatively with moisture content and positively with slope value, electrical conductivity and salt quantity. Reflectivity of halite-dominated crusts was higher than those of gypsum. Halite occurred over a greater range and higher slope values of soils than gypsum; however, a positive correlation between the slope and mean reflectivity of both salt crusts was reported. Although reflectivity of salt crusts varied according to changes in moisture content, and the salinity of the soil, moisture content can drastically reduce the reflection more effectively than the other factors. The data reported indicate the possibility of assessing the type of salt crust by estimation of the ratio of slope and reflectivity to the other variables