Soil quality index (SQI) for evaluating the sustainability status of Kakia-Esamburmbur catchment under three different land use types in Narok County, Kenya

Land and water degradation caused by soil erosion and climate change pose major environmental threats, particularly in agricultural watersheds. Soil erosion in a catchment leads to low crop yields due to declining soil quality (SQ), productivity and sustainability. However, very few studies have been done to assess soil health in Kenya, and none in Narok County. Thus, the aim of this study was to evaluate the soil sustainability status in Kakia-Esamburmbur catchment, based on the identification of key indicators (IKI) from a large dataset (LDS) of 23 indicators, across three land use types designated as grass land (GL), crop land (CL) and forest land (FL). To achieve the stated objective, two soil quality indexing methods were employed: the Additive Soil Quality Index (A-SQI) using the LDS; and the Weighted Soil Quality Index (W-SQI) using Principal Component Analysis (PCA) as a reduction tool to obtain the IKI set. The results show that at a depth of 20 cm, the catchment's soils characteristics did not differ significantly. The two methods (A-SQI and W-SQI) resulted in FL having the highest SQI mean values (0.61, 0.57), followed by CL (0.59, 0.55), while the lowest SQI mean value was recorded in GL (0.58, 0.53). Additionally, the sensitivity analysis showed W-SQI as the most sensitive and superior method in the evaluation of SQI changes due to its high sensitivity and coefficient of variation (CV), at 2.25 and >12 %, respectively. Among the ten IKI, CEC made the greatest contribution to SQ (18.68 %), followed by BD (15.61 %), BIR (14.71 %), Mg (14.26 %), MBN (8.30 %), MBC (8.26 %), Sand (6.77 %), Moisture (5.75 %), TOC (5.16 %), and PMN (2.63 %). The findings show that the catchment belongs to the "medium" category of SQ. The IKI can help save time and reduce the cost of intensive lab works for temporal assessment and monitoring of the effects of different land use on SQ.