156 Journal of the Department of Agriculture. ^ — Aug.. 1IJ22. 



not containing' sodium carbonate. Wafers containing/ Jar;jc (imounts 

 of i^oluhJc salts, not sodium carbonate : These waters can be used with 

 safety only in lands which are naturally or artificially well drained, 

 and when used in such quantities as to cause drainage throupfh the 

 soil so that free water does not accumulate in the soil to be evaporated 

 at the surface, there to deposit the salts dissolved in the water. These 

 waters are only safe when the concentration of the salts in the water 

 used is not such as to be injurious to the plant. The use of such 

 water also requires that surface cultivation be practised largely in 

 order to reduce surface evaporation to a minimum. The salts usually 

 present in such waters are the sulphates and chlorides of sodium, 

 calcium, and sometimes magnesium. These salts do not injure the 

 physical condition of the soil when present in the concentrations 

 usimlly found in natural waters. Waters no't very aUxtiliue : Waters 

 containing' small amounts of salts iu solution can be used on most 

 >oils, but care should be taken not to use large quantities, particularly 

 on soils having poor natural drainag'e, for where the drainage is poor, 

 and larg'e quantities of water are used, the water accumulates in the 

 soil, and having no other means of escape than by surface evaporation 

 or by being' used by the plant, a large quantity is lost in the former 

 way. with the result that the salts contained in this water become de- 

 posited at the surface and there accumulate until the soil becomes so 

 brak as to injure plants. The irrigator who uses saline water must be 

 most careful to see that the natural drainage of the soil is good. If 

 the drainage is poor, he should improve it artificially by means of tiles 

 or open furrows. Surface evaporation must be checked as far as pos- 

 sible by cultivation or by growing a perennial crop, such as lucerne, 

 which retards evaporation by shading the soil. If slightly alkaline 

 waters are used reasonably so as not to accumulate in the soil, and if 

 surface evaporation is largely checked, then there is no great danger. 

 Most people use more than enough water and do not trouble about 

 surface evaporation. Waters containing sodimn carbonate : If an 

 analysis of the irrigation water shows the presence of carbonate of 

 soda — even in small quantities — it should be used with the utmost 

 precaution, and then only on the more sandy soils, for on heavy soils 

 the deflocculation due to the sodium carbonate will, in a few years, 

 bring about such a breaking down of the physical condition of the 

 soil as to preclude the growth of crops at profit. The injurious action 

 of sodium carbonate is not confined alone to the breaking down of 

 the soil granules and thereby retarding the rate at which water and 

 air penetrate the soil — it also corrodes the plant-stem when in high 

 concentration, and dissolves the organic matter in the soil. N012- 

 alkaline icaters containing suspended matter : These are largely flood 

 waters. Flood waters, whether stored in dams or turned at once on 

 to the land, usually contain a fairly large amount of suspended matter 

 made up largely of silt and clay. When such waters soak into the 

 soil they leave as a surface crust a deposit of this fine material. This 

 crust when dry is frequently almost impervious to air and water, and 

 unless stirred may smother the plants, as it were, or prevent penetra- 

 tion of water later on. This fine silt is undoubtedly beneficial to 

 sandy soils; on heavy soils the silt may tend to clog up the pores of 

 the soil, so that muddy waters must be used with discretion on such 

 soils. At any rate, harrowing or cultivation will be essential to break 



