228 president's address — section g (ii.). 



more active acids and alkalies are also formed by the bacteria, and that^ 

 these not only help to complete the weathering of the rock particles 

 in the soil, but also change the phosphates and potash from insoluble to 

 soluble forms. 



THE PLANT FOOD OF THE SOIL. 



All plant life is dependent not only on the amount of nitrogen, 

 phosphoric acid, and potash, but also on the water supply of the soil. 

 How the moisture can be best regulated is too wide a question for me 

 to touch at present. I would merely remind you that in order to pro- 

 duce 1 ton of sun-dried vegetation there has been absorbed by the 

 .roots and transpired through the leaA^es of the plants from 300 to 500 

 tons of water. That is, 1 ton of dried material per acre requires the 

 full utilisation of from Sin. to 5in. of rain. 



Considering first the soils of Australia, I presume that, so far as 

 they go, the results obtained from the analysis and experiment with 

 those of Victoria are fairly applicable to the rest of the continent. 

 We have to consider each of the three chief constituents used by the 

 plant — nitrogen, phosphoric acid, and potash. So far as results of 

 analysis are available, it appears that on the average our soils are as 

 rich in nitrogen as those of Europe or America, and nitrifying processes 

 seem to go on with such rapidity that for the most part, especially 

 in dry areas, there is no need to add this element to the soil in the form 

 of artificial fertilisers. On the wheat lands the addition of nitrogen 

 actually diminishes the yield. Where the rainfall is above 25in., the 

 addition of nitrogen increases the yield of grain, and also the total 

 weight of the crop, but the former effect is not so marked as the latter. 

 For the most part the soil appears to be abundantly furnished with 

 nitrifying bacteria ; all leguminous crops flourish luxuriantly, and, so 

 far as our experiments have gone, the addition of nitrogen-fixing 

 bacteria to the seed has had no apparent effect in assisting the crop. 

 Considering that all animal excreta and farm-yard manure are pro- 

 portionately very rich in nitrogen, it appears practicable, by good farm 

 methods, not only to keep up, but also to rapidly increase the amount 

 that exists on virgin land. The nitrogen problem is important, but 

 by scientific methods it may easily be solved, and at present I think 

 there is no indication that it will become as important as it is in Europe 

 and America. While we are not yet able to explain all the phenomena, 

 it appears certain that in this respect we are favored either by the soil 

 or the climate ; and the marvellous growth which takes place after a 

 few months dry and hot weather would seem to suggest that nitrifica- 

 tion proceeds very rapidly in the soil during the summer. For market 

 garden crops and potatoes, especially on the lighter sandy soils, it is 

 found that a light dressing of nitrogen, in readily available form, ensures 

 a profitable crop ; but for cereals, and for ordinary fodder crops, the 

 cost of supplying the necessary amount of nitrogen is not a serious 

 problem to the farmer, and it appears to me that with improved farm 

 practice it will become even less formidable as general farming takes 

 the place of cereals alone. The presence of lime in suitable amount 

 facilitates the process of rendering the nitrogen available, as will be 

 noticed later on. 



