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Quality of underground water for irrigation
Title:
Quality of underground water for irrigation
Author:
Johns, M. W.
Personal Author:
Publication Information:
Melbourne: Department of Mines, Victoria, 1960
Physical Description:
23 p. : 2 illus., 5 tables, 1 document.
Series:
Geological Survey of Victoria Unpublished Report 1960/103
General Note:
(Reference Abstract -- Abstract ) With an increasing interest in irrigation among farmers more underground water than ever before is being used for agricultural purposes. This is true in areas of relatively low rainfall as well as those of higher rainfall. Many districts in Victoria have underground water which is generally not suitable for any type of irrigation. There are some, too, where the water quality presents few problems when used for the irrigation of almost any crop. It is those waters which fall between these two extreams which are of special interest here. Early investigation of the quality of irrigation water tended to consider only its total content of dissolved soilds. Ranges of salinities were established to represent useful water for certain types of irrigation. In one particular area such as the Mallee country in South Australia, where soil conditions do not show extreme varaiations and where the chemical composition of underground waters derived from the bryozoan limestone aquifer there is fairly constant, this system of establishing the salinity after many years of use has proved of value. In this case fairly saline waters have been used without serious ill-effect. However, waters with the same content of dissolved soilds but of different chemical composition, when used under different conditions of drainage and soil type, may produce poor results. It is evident, therefore, that more of the factors involved in the successful use of a particular water for irrigation should be considered if only in general terms. A more widely applicable system of classification of irrigation waters may then be devised for use by such people as hydro-geologists, who may be connected with the utilization of underground water. An attempt is made here to outline some of the important effects of the use of saline irrigation waters on plants and soils. It is hoped that more use may then be made of chemical analyses in determining the usefulness of a particular type of water for irrigation.

(Conclusions -- Report Conclusions ) The characteristics of irrigation waters which are most important in determining their usefulness area: a. total concentration of dissolved solids; b. relative proportion of sodium to other cations as expressed in the sodium adsorption ratio (SAR); c. concentration of boron or other elements which may be toxic; d. bicarbonate concentration as related to the concentration of calcium plus magnesium. The total dissolved solids of the water must be appraised in terms of the likely salinity of the soil solution which may be several times the salinity of the irrigation water. The salinities of the saturated soil extracts which produce a 50 per cent decrease in yield for particular crops are given in Table 1. Under very good conditions of drainage, etc., it is considered that the maximum salinity of the irrigation water should not be greater than one half of the salinity of the saturated soil extract which causes a 50 per cent decrease in crop yield. The likelihood of alkalization of the irrigated soil can be measured in general terms by the sodium adsorption ratio, but this must be considered in terms of other factors such as soil type, clay content, etc. The more saline the irrigation water the lower the sodium adsorption ratio which can be tolerated. Toxic concentrations of boron in underground water may not be very common although few analyses have been carried out for boron in Victoria. It is likely to occur in small amounts in most underground waters and the possibility of boron toxicity to certain sensitive plants should not be overlooked. The occurrence of "residual sodium carbonate" in some underground waters in Lower Tertiary sand aquifers in Victoria introduces a danger of the formation of alkali soils if these waters are used for irrigation over long periods. Special irrigation practice may be necessary when using saline irrigation water to prevent soil salinization and alkalization.