THE STERILIZATION OF SOIL AS A MEANS TO 
INCREASE ITS FERTILITY. 
The ultimate cause or causes of soil fertility have from the eai- 
liest ages 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 
tittle 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 fiom the 
soil. 
It was soon realized, however, that there was a vast difference 
between the amount of material taken out by a crop and the total 
material present in the soil, and that this theory did not by any means 
explain the facts, since any normal soil coni ains sufficient material, 
e. g., potash, phosphoric acid, calcium, etc., for say a hundred crops, 
an d 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 
present day is to determine what is known as “ available ” potash, 
and phosphoric acid. 
