XL ROYAL SOCIETY OF CANADA 
of the ash of plants and pointed out that in the absence of these mineral 
constituents plant life was impossible. He was also the first to show 
that the ash of the plant contains all the solid materials taken by the 
plant from the soil except the nitrogenous compounds. 
Liebig, in his reports to the Britsh Association in 1840 and 1842, 
demonstrated the importance of having a sufficient supply of the essential 
elements of plant food in soluble condition in the soil so that plants may 
obtain from the land the ingredients necessary for their growth. By 
the middle of the 19th century, it was well understood that nitrogen, 
potash and phosphoric acid were the essential ingredients required. 
which, if not already existing in the soil in sufficient proportion, must 
be supplied or good crops could not be had. 
The chief distinction between the functions of farm manure and 
commercial fertilisers may in a general way be thus stated. Farm 
manure increases crop production by supplying the elements needed in 
about the right proportion for healthy plant growth, and at the same 
time by the addition of humus improves the general condition of the soil, 
while the commerciai fertilisers act directly as plant food, without 
materially affecting soil structure. It is evident, therefore, that com- 
mercial fertilisers are not an adequate substitute for farm manure for 
producing permanent improvement. On virgin soils they are generally 
superfluous, but, as loss of plant food goes on under cropping, if resti- 
tution be not adequately made with farm manure, artificial fertilisers 
may be required. 
The effective and economical use of barn-yard manure is without 
doubt one of the most important problems of modern agriculture for on 
this material the farmer’s hopes of maintaining the fertility of his land, 
and thus providing for a succession of good crops, are mainly based. 
Experiments continued for twelve years at the Central Experimental 
Farm have shown that a given weight of manure taken fresh from the 
barn yard is equal in crop producing power to the same weight of rotted 
manure. It has also been shown by repeated tests that fresh manure 
loses during the process of rotting from 50 to 60 per cent of its weight. 
It is estimated that the farm manure produced in Canada amounts pro- 
bably to about 100 million tons a year. The financial loss involved in 
the wasteful handling of such a vast amount of valuable plant food shows 
the great importance of this subject. 
When we consider that all the food taken from the soil by plants 
must be furnished to the roots in aqueous solution, the necessity of a 
sufficient supply of water is apparent. The quantity of water held in a 
soil at any given period is not wholly dependent on recent ranfall, and 
