Spatial interpolation of vertisol physico-chemical properties through ordinary kriging in south-eastern Zimbabwe

A decline in sugarcane yields from Block G (∼400 ha) of GreenFuel’s Chisumbanje Estate in south-eastern Zimbabwe prompted a study on spatial variability of the soil physico-chemical parameters in the 2017–2018 farming season. Using a systematic gridding schema, 123 geo-located soil samples from 16 sub-blocks were extracted from a depth of 0.3 m and analysed for various parameters. The results showed that pH was slightly acidic to alkaline (6.13–7.95) and had the lowest variability (CV ±15%). Low (N, P, Fe and Zn) and adequate (K and Cu) levels of mineral nutrients were also observed. However, some nutrients were highly variable, with P, Fe and Zn revealing the largest variability (CV ±35%). Semivariogram analysis showed a weak (clay, soil organic matter and N), moderate (pH, P, Mn and Zn) or strong (K, Fe and Cu) spatial correlation between the measured and predicted values. To optimise soil fertility and reduce variations, it is recommended that the estate employ variable-rate fertiliser application technologies, nutrient-monitoring systems, and precision satellite-based guidance for machinery. The study generated soil fertility maps using ordinary kriging; this will serve as a future reference for soil test-based fertiliser recommendations, soil fertility monitoring, and identifying spatial variability on the estate.