165 



heavier rainfall and greater sub-drainage, nitrates are washed 

 out of the soil much more rapidly, and that it therefore becomes 

 rapidly comparatively poor in nitrates, and responds more 

 vigorously to a dose of nitrogenous manure. But it still remains 

 to be explained how it comes about that at Roseworthy, after 

 taking off the land good crops of wheat, &c,, which must neces- 

 sarily remove quantities of nitrogen from the soil, it is still 

 possible, without the addition of nitrogenous manure, to obtain 

 further good crops of a similar kind. Is there such a super- 

 abundance of nitrates or other nitrogen compounds in the soil as 

 to be practically inexhaustible for a long period of time, or is 

 there some process, and if so what, by which the stock of 

 nitrogen is replenished 1 I am not aware whether any data are 

 available as to the total nitrogen supply, but it is improbable that 

 there is any excessive quantity. Whence then does the niti'ogen 

 come ? 



The answer is, according to Professor Lowrie, that it comes 

 during the fallowing process, and probably owing to the influence 

 of minute organisms of some kind, which operate during the 

 process. Observers in other countries have more than once 

 noticed the occurrence on the surface of the soil of minute alga^, 

 such as have already been referred to, and which, you will re- 

 member, have been proved to have the power of fixing nitrogen 

 from the air, though probably they effect this only in association 

 with bacteria. Professor Lowrie informs me that he has a strong 

 suspicion that in this country something similar occurs, from ap- 

 pearances which he himself has frequently noticed on the soil. If 

 that be so, the operation of fallowing becomes one of immense 

 importance, and one to the proper carrying out of which great 

 attention should be given. Clearly that involves a careful series 

 of investigations as to the best time and the best manner of 

 carrying it out. It is not known at present, certainly not in this 

 country, under what conditions of moisture, temperature, and 

 physical condition of the soil these organisms do their best work. 

 It may be stated with confidence, therefore, that a series of 

 careful systematic observations a!-e necessary, involving extensive 

 chemical and biological experiments, to decide upon the best 

 method of fallowing, but at present no satisfactory provision is 

 made for such work. 



I have dwelt at some length on the supply of nitrogen to 

 plants because it is a question of more general scientific interest 

 than others, such as the supply of phosphates, potash, &c. It 

 must not be supposed, however, that everything is known about 

 these other questions. You are aware that in recent years super- 

 phosphate has been used in larger quantities in preference to other 

 forms of calcium phosphate, such as bonedust, &c. In the manu- 



