Salinity guidelines for irrigation: Case studies from Water Research Commission projects along the Lower Vaal, Riet, Berg and Breede Rivers

Abstract

A vast number of projects on salinity in irrigated agriculture were funded by the Water Research Commission (WRC) during the past 40 years. However, due to the diversity of the projects it is virtually impossible to cover all aspects thoroughly in a paper of limited length. Thus this review focuses mainly on projects along the Lower Vaal, Riet, Berg and Breede Rivers in South Africa. The results on the water quality of these rivers indicate that irrigation has led to the deterioration of water sources. There is a direct relationship between river water quality and soils irrigated. Fortunately, effective landsuitability guidelines were developed and applied during the establishment of the major irrigation schemes. This facilitated the management of soils under irrigation. The results from long-term irrigation case studies along the Lower Vaal River and Breede River show that the quality of soils can be improved. The opposite is also true where mismanagement occurred. Research on the salinity threshold of major crops (grapevines, wheat, maize, groundnuts, etc.) confirmed the empiric nature of the guidelines. It is suggested that a more dynamic approach be used for managing salinity under irrigation at farm level, i.e. the use of models. Amongst others, future research should focus on determining the spatial and temporal distribution of salt in irrigated soils.

Qualitative assessment of sediment from River Meghna, Bangladesh

“…Problems associated with salinity in irrigated agriculture had been encountered in some of the areas viz: the irrigation schemes of the Fish and Sundays Rivers in the Eastern Cape (Hall and Du Plessis, 1979), the Riet River in the Free State (Van der Merwe, 1965), the Berg and Breede Rivers in the Western Cape (Cass, 1986) and the Vaalharts Irrigation Scheme in the Northern Cape (Streutker et al, 1981). High levels of salinity has negative effect on soil quality and crop yield (Rensburg et al, 2011). Soil organic matter have exert great influences on the chemical, biological, and physical properties of the soil beneficial to crop production (Dexter and Bird, 2001;Pagliai and Vignozzi, 2002;Wosten et al, 1999)).…”

Perception of Environmental Spillovers across Scale in Climate Change Adaptation Planning: The Case of Small-Scale Farmers’ Irrigation Strategies, Kenya

“…Salinity is recognised as one of the greatest land degradation process and ultimate decline in soil productivity especially in arid and semi-arid regions [93,94]. High levels of salts in water used for irrigation has been implicated to affect soil fertility and crop yield [95]. Salinity hazards or EC exceeding certain threshold levels reduce water availability in the root zone and cause 8-86% drop in crop yields [32].…”

Ecological consequences of global climate change for freshwater ecosystems in South Africa

“…Several river systems already have high levels of salinity, for example, the Berg River in the Western Cape. 35 In comparison, salinity levels in the headwaters of the Murray-Darling Basin in Australia are expected to increase by 13-19% by 2050, 36 a situation that may be mimicked in some southern African regions, indicating that under predicted climate change for this region, salinisation would be exacerbated. The synergistic and antagonistic interactions of several water quality variables make it especially difficult to predict the likely consequences of climate change on receiving water bodies, suffice it to say that these consequences are likely to be significant given the levels of stress already imposed on these systems.…”