INTRODUCTORY 5 



to a substance having a basic reaction. As applied to the 

 soil, however, this restricted meaning does not hold, and 

 alkali refers to any soluble salts that make the soil solution 

 sufficiently concentrated to injure plants. This includes 

 the chlorides, sulphates, carbonates, and nitrates of sodium, 

 potassium, and magnesium, and the chloride and nitrate 

 of calcium. The sulphate and carbonate of calcium are 

 not sufficiently soluble to be injurious to crops. Most of 

 the alkalies are in reality neutral salts. It may be some- 

 what unfortunate to use for general substances a word that 

 also has a restricted technical meaning, but the word 

 has become so well established in agricultural literature 

 that it would now be very difficult to change it. 



Aside from their practical importance, the soluble salts 

 of the soil are of great scientific interest. They offer 

 fruitful fields for investigation to the geologist, the chemist, 

 t^e plant physiologist, the bacteriologist, the mycologist, 

 the agronomist, and the engineer. The complexity of 

 the soil makes the problems connected with alkali very 

 difficult to solve. There are so many interacting factors 

 that no simple statement of the problem can be made 

 and no simple solution arrived at. A complete under- 

 standing of the problem will call for careful researches by 

 investigators in different branches of science and a careful 

 coordination of the findings. The importance of the 

 subject justifies giving it the most careful consideration. 



