179 



Taking the entire 6 feet depth of soil in each case the average per- 

 centages of salts, as far as they may be based on the foregoing determina- 

 tions, are as follows : 



Total soluble Sodium 



ealts. chloride. 



A -0521 



B -0421 



C -189 -0100 



D -530 -1373 



E -966 -3348 



The question now to be pronounced on is : What would be the effect 

 of irrigation upon such soils? Broadly speaking, and having no regard to 

 modifying causes, there can be only one answer. The result of irrigation 

 would assuredly be to raise the bulk of the alkali salts, within the first 

 four feet of soil, to the surface. 



It appears most probable that the low rainfall in the district around 

 Houw Water, accompanied by other causes, prevents the water from ever 

 penetrating the soil to any great extent, and therefore from bringing up 

 the salts during subsequent evaporation. Irrigation would very probably 

 alter all this. The large volume of water led on to the soil is bound to 

 penetrate, and, when evaporation follows, as it undoubtedly must, great 

 quantities of salt will be carried up to the surface, and will accordingly 

 render the surface soil more saline.* 



In connection with some alkaline soils it has been found at Tulare 

 in California that, although the salts in the soil have been drawn up- 

 wards, they have not been drawn right to the surface, and, in spite of 

 the fact that a considerable amount of alkaline salts was present in the 

 soil, there was not sufficient at the surface to cause any interference with 

 the growth of shallow-rooted crops like barley, which flourished, to all ap- 

 pearances, satisfactorily. The reason for this is to be found in the fact 

 that the surface soil was kept under constant cultivation, whereby 

 evaporation from the soil itself was checked, and proceeded instead from 

 the verdure of the cultivated crops. If the land can be kept under con- 

 tinuous cultivation, there would be two simultaneously operating causes 

 at work to retard evaporation, and consequently to prevent the rise of 

 alkaline salts to the surface. Evaporation from foliage instead of from 

 soil would not be the only saving factor, but the shading of the ground 

 by the crops keeps the temperature low, and so further still diminishes 

 the tendency to evaporation from the soil surface. 



It would appear that the most noxious of the Sodium salts, the car- 

 bonate, ia practically absent from the Houw Water soils, the two com- 

 pounds of Sodium which form the bulk of the alkaline soil constituents 

 being the sulphate and the chloride. Professor Hilgard estimates that, 

 for barley, sandy soils should not contain, within the first twelve inches, 

 over *10 per cent, of Sodium carbonate, '25 per cent, of Sodium chloride, 

 or '45 to '50 per cent, of Sodium sulphate; in clayey soils even smaller 

 percentages may prove injurious. It has been calculated that the average 

 proportion of total alkaline salts in the four feet nearest the surface 

 should not exceed "2 per cent, if barley is to be grown. According to 

 Professor Hilgard's experiments, as already stated, barley thrived on a 

 soil which contained on an average *159 per cent, of alkaline salts in the 

 first four feet; on the other hand, the cereal refused to grow where the 

 average amount in the first four feet reached '203 per cent. Now, of the 

 Houw Water soils it seems likely that A would satisfy this condition, and 

 so too possibly B; the average percentage in C is '186, but both I> and E 

 are considerably on the worse side of the danger limit. 



These remarks are obviously made on the supposition that the drainage is< 

 inadequate. 



