37 



Every one is familiar with the fact that too concentrated fertilizers 

 may produce death to the plant, and it may be by this action. Apply- 

 ing the principle to the alkalies in the soil, it must be recalled that 

 these compounds are all relatively very soluble in water, so that if 

 only large quantities of water containing even small amounts of the 

 salts are evaporated in contact with the roots of growing crops, the 

 solution surrounding the soil grains may become too strong for good 

 plant feeding, and even death may result. ... 



HOW ALKALIES ACCUMULATE IN THE SOIL. 



Everywhere in the soil where there are sufficient changes in the air 

 and the moisture, the soil grains are being broken down and dissolved 

 by both physical and chemical means, and unless the rains are suffi- 

 ciently heavy to carry the ever-forming dissolved salts away in the 

 country drainage, they will be brought to the surface by capillarity 

 and there concentrated until precipitated. The more insoluble of the 

 plant-foods, and other salts which are not such, cannot charge the 

 water sufficiently high to do serious harm, hence in common language 

 and in the sense the term is here used, they do not become " alkalies." 



But with the other salts the case is different. They are precipitated 

 when the solution becomes strong enough, and form deposits on the 

 surface or about the roots in the soil where water is being removed, 

 but before this actually occurs one or both of the actions referred to 

 above begins to take place. 



In arid regions, where the alkalies proper are most abundant, rains 

 enough may fall to slowly carry forward their formation, but not 

 enough to carry them out of the land. From the higher levels and 

 steeper slopes they are readily moved by surface drainage and wind 

 action to the lower lands, where the amount may become so large as 

 to form thick beds. During the wet seasons of such countries, these 

 salts may sink into the soil, but to rise again when dry weather re- 

 stores the action of capillarity. 



In the humid regions, there is necessarily an even more rapid for- 

 mation of all the true alkalies of arid climates ; for fundamentally 

 similar rock ingredients are subjected to identical weathering processes, 

 but of a more intense nature, because the rainfall is greater. If, 

 therefore, there occur conditions favourable to the accumulation of the 

 soluble salts formed at and near the surface of the soil, these should 

 be expected to show as alkalies. . . 



INTENSIVE FARMING MAY TEND TO THE ACCUMULATION OF ALKALIES. 



It has already been pointed out that during the growing season 

 after vegetation has come into full action, nearly all of the rains which 

 fall in humid climates are retained near the surface until they are 

 evaporated, either through the growing crop or from the soil, and since 

 these waters tend to form salts when they are in contact with the soil 

 grains, they must tend to increase the salt content near the surface. 

 It is plain, too, that the heavier the crops produced and the greater 

 the number of them in the season, the less is likely to be the loss of 

 any water from the field by under-drainage ; hence the greater the 

 •tendency for soluble salts to accumulate. Then, if during the winter 

 season of a country the rainfall is deficient, so that little leaching can 

 take place, conditions become still more favourable for the accumulation, 

 of alkalies. 



