482 



THE STERILIZATION OF SOIL AS A MEANS TO 

 INCREASE ITS FERTILITY. 



The ultimate cause or causes of soil fertility have from the ear- 

 liest aj^cs remained obscure and when one realizes that the practice or 

 art of Agriculture is the oldest in the world, this obscurity is perhaps 

 somewhat remarkable to the lay mind, although not to the scientific 

 investigator who has tried and is still trying to evolve theories and 

 explain facts from the vast amount of experience in the past from 

 which he is able to draw. 



As soon, however, as one begins seriously to consider the subject, 

 its immensity is apparent and it is realized how many are the factors 

 which influence what we describe as soil fertility. 



The facts are, however, sufficiently realized by the practical 

 man whether planter or farmer who is ready to pay two or three 

 times the amount for a certain ipiece of land compared with another. 



The science of Agriculture dates back to the seventeenth century 

 but the work done by numerous investigators in the early years bore 

 little fruit, due principally to the fact that the science of chemistry 

 had scarcely been born, and it was not till the nineteenth century 

 when the nature of the elements and their combinations began to be 

 known that agricultural chemistry as a science was really founded. 



It was not till nearly the middle of the nineteenth century that it 

 was understood that the plant derived its nutrition partly from the air 

 and partly from the soil, and the first theory which was in any way 

 supported by facts that soil fertility was based on the amount of the 

 material required by the crop and capable of being removed from the 

 soil. 



It was soon realized, however, that there was a vast difference 

 between the amount of material taken out by a crop and tlie total 

 material present in the soil, and that this theory did not by any means 

 explain the facts, since any normal soil coniains sufficient material, 

 e. g., potash, phosphoric acid, calcium, etc., for say a hundred crops, — 

 and yet a very small quantity of a suitable manure gave remarkable 

 increases of crop. 



This naturally led up to another theory — that of " unavailable " 

 and *' available " plant food, — the latterlbeing in some way only slow- 

 ly formed in soils — the addition of a manure would thus really mean 

 the addition of available food. 



This theory was forgotten and renewed again within quite recent 

 years and in fact one of the recognised methods of soil analysis of the 

 l^resent day is to determine what is known as " available " potash, 

 and phosphoric acid. 



