South African Water Quality Guidelines
Volume 4 — Agricultural Use: Irrigation

Salinity — Total Dissolved Solids / Electrical Conductivity

TDS and EC are directly related — EC is measured routinely as a proxy for TDS.

Table 2 — Relative Salt Tolerance of Various Commercial Crops at Germination (after Ayers & Westcott, 1985)

The main Salinity criteria (above) don't account for growth-stage differences — germination is markedly more salt-sensitive for some crops than the mature-plant tolerance implied by the main table. EC of the saturated soil extract causing a 50% reduction in emergence.

Table 3 — Commercial Crops Classified by General Salt Tolerance (After Maas, 1990 and Ayers & Westcott, 1985)

Grouped by crop family across three sub-tables (3a–3c). A fourth sub-table (grasses & forage, 3d) and the ornamental-plant table (Table 4) are dense multi-crop lists in the source and are reproduced as continuous text further below rather than split per-crop.

Table 3a — Fruit & Nut Crops

Table 3b — Vegetables

Table 3c — Fibre, Seed & Sugar Crops

Table 3d — Grasses & Forage (reproduced as continuous text — see note)

This sub-table packs many multi-word species names per cell in the source with no per-item delimiter; boundaries below were reconstructed for readability (comma = variety/qualifier, e.g. "Clover, red" = red clover) and cross-checked against the standard Maas (1990) forage table, but individual entries were not run through the searchable lookup above out of caution — verify a specific species against the source PDF if precision matters.

Table 4 — Ornamental Shrubs, Trees & Ground Covers (After Maas, 1990 — reproduced as continuous text)

Same caveat as Table 3d above — cultivar annotations (cv. ...) reconstructed for readability, not individually searchable.

pH

A three-way effect — pH outside range disturbs crop yield/quality, soil nutrient availability, and irrigation equipment simultaneously.

Sodium Adsorption Ratio (SAR)

Table 2 — Effects on Soil Physical Conditions

SAR's effect on infiltration/hydraulic conductivity is EC-dependent — a higher irrigation-water EC offsets SAR's destabilising effect on soil structure, so each band's "problem" threshold is itself a moving EC value, not a fixed one.

Table 4 — Susceptibility of South African Soil Types to Physical Deterioration due to ESP–EC Interactions

General guidance only — requires modification for local rainfall/weathering and parent material; expert opinion should be sought for critical decisions.

Letters refer to the South African soil groupings below (typical soil forms in each):

Table 3 — Relative Tolerance of Crops to Exchangeable Sodium Percentage (ESP)

Tolerance decreases down each column's implied order is not preserved here (crops re-sorted into class lists); tolerances are relative — nutritional and physical soil factors often limit growth before the listed ESP is reached.

Sodium — foliar absorption (sprinkler irrigation)

Chloride

Table 2 — Relative Susceptibility of Crops to Foliar Injury from Saline Sprinkling Waters

Applies when sprinkler irrigation wets crop foliage directly; daytime sprinkling under hot/dry conditions needs more conservative criteria. Tobacco is a special case — quality (not yield) is affected by chloride above 25 mg/L even though it isn't listed in a class here.

Table 3 — Annual Crops Grouped into Chloride Tolerance Classes (Threshold Cl⁻ in Saturated-soil Extract)

Threshold concentrations are reproduced exactly as printed in the source table — note they don't increase strictly monotonically between the middle columns in the original document. Treat this table primarily as a relative crop ordering (per the source's own note, tolerance increases within a column) rather than as precise mg/L cut-offs; use the Chloride root/foliar table above for the authoritative concentration thresholds. * = less tolerant during emergence/seedling stage.

Boron

Inorganic Nitrogen

Scaling / Corrosion — Langelier Saturation Index

Aggressiveness Index (AI)

AI = pH + log₁₀(Total Alkalinity × Calcium Hardness, both as mg/L CaCO₃) — formulated for evaluating corrosion specifically in asbestos-cement pipe.

Ryznar Index (RI)

RI = 2·pHs − pHa (pHs = Langelier saturation pH, pHa = actual pH); equivalently RI = pHa − 2·LI.

A fourth index (Corrosion Ratio, R) is also given for chloride/sulphate-driven corrosion: R < 0.1 indicates general freedom from corrosion in neutral-to-slightly-alkaline oxygenated water.

Suspended Solids & Faecal Coliforms — drip emitter clogging

Trace Elements & Heavy Metals

All 17 follow the same three-tier pattern: target range → maximum for fine-textured neutral/alkaline soils → short-term, site-specific use only. Units mg/L unless noted. Most of these guidelines are explicitly marked tentative in the source document, based on comparatively limited data.

Arsenic — Crop Yield vs. Crop Quality (separate norms)

Unlike most trace elements above (collapsed to a single "effect" column), the source gives arsenic separate Crop Yield and Crop Quality criteria — both are protected by the same three-tier concentration bands, but for different reasons.