Assessment of spatial variability of selected soil chemical properties in a communal irrigation scheme under resource-poor farming conditions in Vhembe District of Limpopo Province, South Africa

Abstract

An understanding of spatial variability of chemical soil properties is necessary for proper nutrient management. Therefore spatial variabilities of soil pH, P, K, Ca and Mg in communal irrigation scheme under resource-poor farming conditions were determined. A total of 230 soil samples were collected from two soil depths (0 to 30 and 30 to 60 cm) at 100 m grid intervals. Basic statistics and geostatistical analyses of the data were performed using SAS 9.0 and GS+ 9, respectively. Soils showed high variabilities for all variables that were analyzed. Soil pH exhibited the lowest CV (6.0%) for both layers whereas all other measured variables displayed high CV for both soil layers. Most properties were analyzed by exponential model except for Ca and Mg that were fitted into spherical and Gaussian models respectively. All variables that were fitted into exponential model had strong spatial structure and those fitted into spherical model had a moderate spatial structure. Kriged contour maps displayed positional relationship between the topsoil and subsoil layers. Areas with low K and P can be delineated into separate management zones based on their requirements for these elements. The study showed that geostatistics is a useful tool to map spatial variabilities of soil chemical properties even under resource-poor farming conditions. These maps can be used to encourage/implement variable-rate of input application and inform resource-poor farmers of the benefits of this strategy, thereby reducing variation in soil fertility status caused by application of indiscriminate types and rates of manure and fertilizers. Key words: Site-specific soil management, soil layers, Kriged contour maps, geostatistics, exponential model, South Africa.