[shutt-smith] "ALKALI" CONTENT OF SOILS 85 



which assists in the germination of the seed and is the means of con- 

 veying food to the plant rootlets; for the performance of these import- 

 ant functions it is obvious that it should possess no injurious properties. 

 The effect of a solution such as we find in alkali soils on the cells in 

 the tissues of the roots is to extract or withdraw from them by osmosis 

 their natural water. As a result the cells lose their turgidity, their 

 protoplasmic contents shrink from the cell wall, the plant wilts and 

 death may ensue. The higher the percentage of alkali — in other 

 words, the more concentrated the solution — the more severe the effect 

 in this direction. Chlorides are more injurious than sulphates. 



"Black" alkali is much more injurious than "white" alkali. 

 The sodium carbonate it contains is directly corrosive, causing injury 

 at the base of the trunk or root crown of the plant, by cutting into 

 and eating away the tissues. The bark of green herbaceous stems is 

 usually turned to a brownish tinge for half an inch or more imme- 

 diately above the surface of the ground, becoming soft and easily 

 peeling off. The rough bark of trees is found to be almost black and 

 the green layer underneath, brown. Very small quantities are 

 sufficient to prevent seed germination or to destroy the tender rootlets 

 of the seedling, if the young plant appears. 



All kinds of alkali have a tendency to destroy a soil's tilth, but 

 this is particularly marked in the case of black alkali. The soil 

 readily puddles, flocculation, or the property of forming flakes, is 

 destroyed and the land becomes in a large degree impervious to water. 

 On drying hard refractory masses are formed and the soil is extremely 

 difficult to work. Very frequently a hard, practically an impenetrable 

 hard-pan forms under such soils, making it almost impossible to put 

 in a system of tile sub-drainage. 



Crops differ greatly in their susceptibility to alkali; some are 

 so resistant that they may thrive and come to maturity on soils that 

 for the majority of farm crops there can be no possible hope of success. 

 Apart however, from this question of relative resistancy of crops, the 

 composition, concentration and vertical distribution of the alkali and 

 the physical character of the soil are all important matters in reaching 

 a conclusion as to the desirability and safety of placing an affected 

 area under irrigation. Injudicious or excessive application of irriga- 

 tion water, to soils impregnated with alkali especially if the subsoil 

 is of an impervious character and sub-drainage is not provided, may 

 ruin, by bringing up alkali, what would otherwise be excellent land 

 for cultivation under "dry-farming" methods. The irrigation of 

 impregnated land without efficient drainage — natural or artificial — 

 almost invariably gives rise to "rise of alkali" — and this in the past 

 has been a fruitful cause of the ruination in the Western States of 

 large areas of once cultivable, fertile soil. 



