2.2. Physicochemical Analysis of Maize Rhizosphere and Bulk Soils

After soil sampling, 20 g of each sample was air-dried, mixed and sieved using a 2 mm pore sieve to remove dirt. The pH of samples was measured using a pH-meter after mixing with distilled water at a ratio of 1:2.5 soil. The soil organic matter (OM), organic carbon (Org-C) and total carbon (Total C) were determined using the method in Walkley and Black [32] and Shi et al. [33]. According to the method adopted by Deke et al. [34], exchangeable potassium (K) was measured using a flame photometer, while available phosphorus (P) content was obtained using a spectrophotometer. Soil sulfate was determined using the method by Walker [35]. The nitrate (N-NO₃) content of samples was determined using LAQUA twin nitrate ion meter (B-742) [36], while ammonium (N-NH₄) content was measured using a modified manual calorimetric procedure for measuring ammonium in soil and plant Kjeldahl digests as adopted by Baethgen and Alley [37].