Simulated rangeland conditions and seasonal variations influence soil quality in semi-arid central South Africa

Abstract

The study examined long-term effects of rangeland conditions and seasonal variations on soil quality without confounding grazing effects. Samples were collected seasonally from good, moderate, poor, bare and cultivated rangeland conditions at soil depths of 0–10 cm and analysed for bulk density, organic matter, carbon, nitrogen, active carbon, microbial biomass, nutrients and cation exchange capacity. Field measurements of penetrometer resistance, soil temperature, and infiltration rate were taken seasonally or weekly. Bare and cultivated plots had higher penetrometer resistance and soil temperature, but lower infiltration rates compared to good, moderate and poor conditions throughout the year. Regardless of seasonal changes, losses averaging to 22–80% of organic matter, carbon, nitrogen, active carbon and microbial biomass were recorded in bare and cultivated plots. Soil pH, potassium, calcium, magnesium and cation exchange capacity followed similar patterns, while phosphorus, was higher in the bare and cultivated plots during spring. During winter, phosphorus levels in the cultivated plots was only higher than those in bare and poor conditions. Principal Component Analysis distinguished soils in good, moderate and poor conditions as healthier than in bare and cultivated conditions, suggesting that maintenance of vegetation as soil cover has the potential to improve soil quality in semi-arid rangelands despite seasonal variations.