Influence of water quality on crop yield

The quality of irrigation water is crucial to crop yield.? Should the salt content of the water not be suitable for the crop, climate, or soil type, then a planned production venture may be uneconomical.? For that purpose, water quality is expressed in a specific way, for example, S1C1 (the best class) up to S4C4 (the worst class), with any variation in-between. In the class identification code, “S” relates to the sodium hazard (sodium absorption ratio) and “C” to the salt hazard (electrical conductivity).

According to the sodium absorption ratio, water is divided in four classes, namely:

1) Low sodium (S1); Suitable for irrigation where a negligible hazard exists.

2) Medium sodium (S2); Mainly suitable for sandy soils with good drainage ability. On clay, soil salinity will develop in time. The addition of gypsum?is advisable on sandy soils.

3) High sodium (S3); Unsuitable for use on soils with restricted drainage. Use only on well-drained soils with special management.

4) Very high sodium (S4); Not suitable for irrigation because of high sodium content.

Furthermore, according to the electrical conductivity of the water, the salt hazard in the water is divided into four classes, namely:

1) Low salt content (C1); This water holds no salinity hazard on well-drained soils.

2) Medium salt content (C2); Provision must be made for a reasonable degree of salt leaching and saline-sensitive crops must be avoided.

3) High salt content (C3); Can only be used on well-drained soils. Periodic leaching is necessary, and salt-resistant crops must be used.

4) Very high salt content (C4); Not suitable for use as irrigation water under normal conditions. Can be used as an emergency measure, under extreme conditions, on sandy soils.

Consult a Kynoch Agriculturalist to assess your irrigation water and optimise crop yield and quality. Reach us on 011 317 2000 or visit www.kynoch.co.za.

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Credit: Lunay de Kock, Kynoch Fertilizer

Source: Fertilizer Handbook, 2007, FSSA