GIS-aided soil mapping of fallowed land for improved nutrient management on a ferralsol at MUARIK

Abstract

Spatial variability in soils is as a result of variation at multiple scales ranging from point measurements to global. This is exhibited when a parameter of soil measured at different spatial locations exhibits values that differ across the locations. Almost all soil properties exhibit variability as a result of dynamic interactions between natural environmental factors. This research therefore aimed at assessing the spatial variability of organic carbon, total nitrogen and soil pH in a Ferralsol under bush fallowing as well as constructing soil chemical property maps. Thirty (30) soil samples were collected from an area measuring 1 ha and sampling was done systematically. The sampling design involved establishing grids of 20m x 20m where one composite soil sample was collected from each grid at 0-20cm depth and the area was geo-referenced with GPS coordinates. The samples were analyzed from soil laboratory in School of Agricultural Sciences of Makerere University. GIS was used to spatially analyse the results with ARCGIS 10.3 then interpolated and geostatistcally analyzed using inverse distance weighting. The results showed that Soil pH showed no substantial variations from the different parts of the field, TOM was considerably high in the soil throughout the field as seen in the descriptive statistics and this is because the maximum value of TOM (6.282%) was above the critical value of 3% (Okalebo, 2002). The field being under prolonged fallow period. TN had a maximum of 0.303% which is also slightly above the critical value of 0.2% (Okalebo, 2002). From the results, soil chemical properties in this plot vary generally despite being under same management. This was so because of the inherent soil properties those include parent rock material and slope gradient. Hence this plot would require precision crop management.