4 president's address, 



they may be made use of by growing plants. It will not do for 

 one or other to be abundant in one locality and the reverse in 

 another, nor should, for instance, nitrogen be in a form in the 

 soil which plants cannot absorb. Crops, like human beings and 

 animals, must have plenty of food and it must be of a kind that 

 they can make use of. Now farmers must recognise that if they 

 continue growing crops, including grass, and by their removal from 

 the ground they do not allow nature to follow its ordinary course 

 whereby those plants would wither, decompose and return to the 

 soil, they are actually decreasing the food siipply in the soil for 

 any future crops which may be put into it. They must recognise 

 that this plant food supply has been accumulated in the soil by 

 exceedingly slow degrees, by the slow weathering and washing 

 or blowing down of virgin rock, the gradual decomposition of 

 vegetable matter, and then the mixing of these substances by vari- 

 ous means such as the action of water and the activity of different 

 kinds of organisms always at work, such as worms and bacteria, 

 and if these slowly accumulated resources of food supply are 

 drawn upon continually and in a rapid manner by the growing 

 of grain and root crops without giving nature sufficient time to 

 replenish these substances the soil must very soon diminish the 

 supply necessary for plant life, and unless farmers are prepared 

 to come to the assistance of nature and by artificial means replace 

 in the soil that which they had removed therefrom the inevitable 

 result must be that the land will become unproductive. 



I will now refer briefly to the chemical substances which are 

 considered necessary for plant life and whence they are derived : 

 Carbonic acid, one of the compounds contained in air, and from 

 which the plant draws its main sustenance in the shape of carbon ; 

 Nitrogen, another element contained in air to the extent of nearly 

 four-fifths of its volume and which is present in a solid form in 

 fertilisers such as Nitrate ; Phosphoric acid, usually in combina- 

 tion with lime as calcium jihosphate and occurring in commerce 

 as bone ash. The super-phosphate of lime is a phosphate such as 

 bones ground in a powder and dissolved in sulphuric acid. 

 Magnesium, one of the primitive earths ; Potash, an alkali obtained 

 from the ashes of plants and is naturally present in the soil as a 

 result of the weathering of the older rocks ; Calcium, an elementar}^ 

 body and the base of lime or chalk. 



Oxygen is also necessary as plants must breathe, and is obtained 

 by every plant through every portion of it, and as the roots as well 

 as its leaves and branches can absorb oxygen it is necessary that 

 the soil in which a plant grows should be kept loose or porous. 

 As both carbonic acid and oxygen are obtained by plant life from 

 the air it is not necessary for me to deal with them further in a 

 subject such as the present which is concerned with what plants 

 take out of the soil. Nitrogen in the combined form is taken 

 by plants from the soil by means of their roots, but in some cases 

 and by a process not yet fully understood, leguminous plants 

 have the power of assimilating nitrogen directly from the aif. 

 Nitrogen in soil is generally in combination with some other sub- 

 stance and being in this form not soluble it is not in a fit condition 



