Brak in its Relation to Irrigation. 23 



Are Bkak AVatees Usable uxder Certain Circumstances ? 



Connected with the rise of lirak the question of the use of brak 

 water may he considered. 



If the water contains sodium carbonate and it is used on stiff 

 soils tliese latter will he rendered more difficult to till and perhaps 

 quite impermeable to water. 



This is particularly the case with waters which remain muddy 

 for a long time on account of the sodium carbonate they contain. On 

 the other hand a very loose soil is much improved by irrigation with 

 such a water. 



Lands which are irrigated witli sodium carbonate waters should 

 be manured with gypsum, v.hicli will destroy the sodium carbonate. 



Frequently an effect of using sodium carbonate waters is to 

 produce an impervious layer at a greater or less depth below the 

 surface. This layer has the effect of restricting the penetration of 

 roots and also of reducing the amount of water that can be used in 

 one irrigation. If the water is also a muddy one the ef5:ect is similar, 

 but often the top soil is so hadl\- affected that it will not let water 

 through it sufficiently fast. Cultivation helps in such cases at first, 

 but in the end becomes more and more difficult owing to the 

 deteriorated physical condition of the soil. 



If a water does not contain sodium carbonate, but is otherwise 

 highly charged with salts, it may sometimes be used with advantage. 

 As to whether this can be done will dejjend on the degree of brakness 

 and on the manner of usage. Such waters can only be used on soils 

 that are highly permeable to water and possessed of excellent under 

 drainage. Such a water must permeate deeply and pass out as 

 drainage. It must therefore be used in heavy waterings. Under no 

 circumstances should these be light, unless they are immediately 

 followed by irrigation with good water, the combined irrigations 

 being sufficient to cause the necessary penetration and drainage. In 

 this way a brak water may be used to eke out an inadequate supply of 

 fresh water. 



Leakage from Canals and Fijrrgws. 



Where canals run through sandy land or other porous strata a 

 good deal of trouble is experienced and lands are eventually ruined. 



Canals usually occupy the higher levels of the land they irrigate. 

 The water which seeps from them not only tends to fill tip the soil in 

 the vicinity of the leakage, but also travels underground along a line 

 of natural drainage and may eventually find its way into a river. 

 If, however, the rate of travel is not sufficient to keep pace with the 

 seepage from the canals the soil will gradually fill up with water 

 But before this happens much damage will have been done. 



The rising water-table will kill out lucerne and other deep-rooted 

 cultures in the worst type of case ; in others the crop will become 

 unthrifty. The reason for this is that t ,e bottom roots get drowned. 

 If the lands are sloping signs of trouble are often first noticed in the 

 lower lying lands, which ma^' become permanently moist right to the 

 surface. If the soil throtigh which the seeping water passed contained 

 much brak a lot of it will be accumulated in these lower lying lands. 

 Now a waterlogged soil is bad enough, but when an excessive quantity 



