KNOWLEDGE
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Expertise

The influence of water quality on crop production

By Kevin Fourie: Agronomist: Northern Cape Business Unit

There has been increasing use of poor quality irrigation water in the past decades due to the scarcity of fresh water resources. Highly saline water from various sources such as industrial and domestic waste waters and sewage effluents are more commonly re-used and recycled for irrigation purposes. Secondary salinisation of the soil profile and/or ground water is the result of irrigation with poor quality water. South Africa has an estimated 1.3 million ha under irrigation and 20% of that is already salt affected due to secondary salinisation. Reduced crop yield and quality, unsuitability of soils and various health risks are of the many impacts to be found with the use of poor quality saline water for irrigation. There are various water quality characteristics to take in consideration to determine its suitability for irrigation, but the main determinants are the salinity and sodicity and its effects on the plant-soil-water continuum.

More focus should be given to the principal plant responses to poor irrigation water. Crops differ in their reaction to water quality (Figure 1); some are more tolerant to salinity stresses then other crops, thus, choosing the best crop to use the resources is of utmost importance.  

Various factors influencing salt tolerance:

Soil fertility

OmniPrecise™ and OmniBio™ can be used to very accurately determine the soil's fertility and biological status. Soil fertility can then be improved and the salinity status reduced to restrict yield losses, whether it is by applying differentiated fertilizer of gypsum.

Soil physical conditions

Soils can be classified, to determine the structure or impermeable layers that restrict root growth and influence the distribution of water and salt in the soil, by highly trained specialists on the OmniPrecise™ team.

Irrigation methods

The salt tolerance of crops also depends on the type and frequency of irrigation, due to the fluctuation in salt concentration between irrigations. The method of irrigation affects the depth of irrigation, runoff, deep percolation losses, uniformity of application and thereby salinity. By using the data gained with the OmniPrecise™, efficient irrigation systems can be identified and applied to differentiate the irrigation scheduling, as well as the optimisation of salt additions.

Stage of growth

Crops sensitivities changes considerably during the development of the plant. Most plant are tolerant during germination but are more sensitive during the vegetative stages. By using OmniSap® during the various growth stages (Figure 2), the nutrient imbalances can be attended to to minimise the effect on yield.

Quantifying salinity diagnosis

Irrigation water quality can be analysed by the Omnia Lab throughout the growing season to monitor the salinity levels. This data are then incorporated in a model to classify and measure the various salts that influences the normal crop growth.

Summary

By using the technology and expertise available in Omnia, the detrimental effects of salinity on normal crop growth and yield can be determined and limited to restrict the risks and variations for the farmer regarding water quality, and to provide a service to support and advise to deliver top yield.