Quantification of primary salinity, sodicity and alkalinity in South African soils using climate regions

Abstract

No reliable primarily salinity, sodicity and alkalinity information is available for South Africa, nor are there monitoring programs in place to track the salt-affected status of South African soils. Such information is, however, needed for various agricultural and environmental studies on a provincial and national scale. Natural geological, hydrological, geomorphological and pedological processes lead to the development of most salt-affected soils. The aim of the study was therefore to determine the baseline salinity, sodicity and alkalinity of South African soils as related to selected climatic parameters. Soil analyses from the Agricultural Research Council–Institute for Soil, Climate and Water (ARC-ISCW) soil survey database were used in this study. Data from the ARC-ISCW and the South African Weather Service weather stations with a recording period of five years or more were used to determine temperature, rainfall and evaporation statistics. The aridity index (precipitation/evaporation) was used to express aridity. No clear relationship was observed between rainfall, evaporation, and aridity and salt accumulation on a national scale and other factors, such as geology, position in the landscape and previous climatic conditions, should also be accounted for. The relationship between climate and salt-affected soils was difficult to determine, probably because of the paleoclimate differing from the present climate. Thus, not all salt-affected soils showed predictable associations with present-day climate.