**2. Materials and methods**

Soil samples were collected from all transect points with three replicates around each point, at 0–10, 10–20, 20–30, 30–40 and 40–50 cm depths with a bucket auger. Samples from each depth per transect were mixed to get a composite sample and were oven-dried at 38°C for 72 h, ground with a mortar and pestle, and sieved (< 2 mm). Particle size analysis was only done for the 10–30 cm depth, after removal of the top 0–10 cm depth, which was mainly made up of OM. Particle size analysis was conducted using the double pipette procedure after removal of OM with hydrogen peroxide (H2O2) and dispersion with sodium hexametaphosphate solution [19]. Soil pH was determined in H2O (1:5 soil: water). Total C was determined using a Leco TruMac CNS/NS Determinator (Leco Corporation). The available P was extracted with 0.25 M ammonium bicarbonate, EDTA disodium salt and 0.01 M ammonium fluoride (AMBIC) solution [20] and analyzed following the molybdenum blue calorimetric method [21], using the UV/VIS spectrophotometer Thermo Fisher Scientific model Genesys 20.

Total heavy metal concentrations were analyzed after extraction with aqua regia [22]. Soil samples (0.5 g) were treated with 12 ml concentrated HCl (32%) and 4 ml concentrated HNO3 (55%) and digested in a microwave digester (EPA 3051H-HP500) at 175°C for 10 minutes. An aliquot of the digest (5 ml) was diluted to 50 ml with

de-ionized water, in acid-washed glass test tubes, and analyzed for Zn, Cu, Ni, Cr, Pb, Cd and As with an inductively coupled plasma optical emission spectrometer (ICP-OES 720 Varian). The results were compared with total maximum thresholds (TMT) and maximum permissible limits (MPL) from the WRC South Africa [23]. The TMT is the concentration of the metal beyond which the risk to the environment is unacceptable, while MPL is the concentration beyond which further waste disposal is prohibited.
