Mapping spatial distribution of soil properties using electrical resistivity on a long term sugarcane trial in South Africa

In experimental trials the spatial distribution of soil properties is a key factor to evaluate and determine the credibility of the research outcomes. To evaluate the spatial distribution of soil properties at different depths in the present study, the electrical resistivity method was selected because of its non-destructive nature and high spatial resolution. The investigation was conducted on BT1 (Burning versus mulching) the world's oldest sugarcane trial (established 25 October 1939) located on the premises of the South African Sugarcane Research Institute (SASRI). The experimental area, covering 7200 m2, is divided in 32 plots with three crop residue retention treatments. These treatments are either fertilized and not fertilized. The RM15 resistance-meter equipped with a multiplexer was used to collect geophysical data. The latter was used to generate apparent electrical resistivity maps corresponding to three approximate depth ranges: (0–0.5 m, 0–1.0 m and 0–2.0 m). The spatial resolution of the shallowest map (0–0.5 m), was 0.5 m × 1.0 m. Bulk density and soil water content, for the 0–0.1 m depths, were also determined from samples collected on a grid of 4 m × 5 m. All data collected were georeferenced using a spatial resolution of 4 m × 1 m with the Digital Elevation Model (DEM). The results of this survey showed the effectiveness of geophysical mapping to reveal detailed information regarding soil spatial variability and to understand and establish the relationships between soil fertility and soil physical properties. Detailed analysis of these results led to the identification of two different soil types on the trial site: a Mollic Cambisol in the upper slope of the trial with a depth of