Soil quality characteristics of kikuyu–ryegrass pastures in South Africa

Development of a soil quality index for kikuyu (Pennisetum clandestinum)–ryegrasss (Lolium spp.) pasture systems in the southern Cape of South Africa is important since there are certain warning signs that their sustainability is being threatened. A total of 142 pastures throughout the region were sampled and several soil physical, chemical and biological indicators were quantified. A minimum data set of the most sensitive indicators was chosen using principal component analyses. Linear scoring functions for these indicators were used to develop a soil quality index. The most sensitive indicators were: extractable P>gravel content>water holding capacity (WHC)>exchangeable acidity (EA)>soil organic matter (SOM)=penetration resistance (PR)>exchangeable Mn. The soil quality index (SQI) was equated as: SQI=0.13 (PR)+0.16 (Gravel)+0.15 (WHC)+0.14 (EA)+0.17 (P)+0.12 (Mn)+0.13 (SOM). This soil quality index is appropriate for pasture systems in the southern Cape of South Africa, and may be useful for similar pasture systems in other areas. •A soil quality index was developed specifically for pasture systems in South Africa.•The minimum data set was selected using principal component analyses.•The index included physical, chemical and biological indicators.