the most interesting results is that all the water in a normally moist 

 soil is held in the same way and there is no break in physical state : 

 the distinction that used to be made between free water and hygro- 

 scopic water could not be found in these experiments. The agree- 

 ment between the experimental curves and those deduced from the 

 formula shows that we have now got at the various factors involved 

 and can proceed to work up our field results. 



Equally important with the water supply is the air supply in 

 the soil : this has been under investigation in conjunction with Mr. 

 Appleyard. Periodical analyses extending over nearly two years 

 on several typical plots have shown that the free air in the soil pore 

 spaces differs only slightly from atmospheric air in regard to oxygen 

 content : there is, however, a greater difference in carbon dioxide 

 content. These results agree so closely with those obtained else- 

 where that we may regard the similarity of soil air to the atmosphere 

 as generally true. But the investigation revealed something that 

 has not before been observed. It was found that in addition to the 

 free air of the soil there is a second atmosphere dissolved in the soil 

 moisture and colloids, which is entirely different in composition; 

 containing no free oxygen but mainly carbon dioxide and some 

 nitrogen. It is this atmosphere which is in most intimate contact 

 with the plant roots and micro-organisms, and its lack of oxygen 

 proves that the oxygen is used up more rapidly than it is renewed 

 by solution from the free air. 



These results have materially helped our investigations on the 

 biochemical changes in the soil. It has been explained in previous 

 Reports that the nitrogen compounds occuring naturally in the soil 

 or added as manure break down under the action of micro-organisms 

 to form nitrates and gaseous nitrogen ; the former being wholly 

 valuable and, in this country, commonly limiting the fertility of the 

 soil ; while the latter is wholly waste and, so far as can be seen, of 

 no value whatever to the cultivator. 



The study of these changes is perhaps the most important of 

 soil fertility investigations. Much of the work in the past has been 

 done in the laboratory, but this year it has become possible to carry the 

 investigation into the field. During the past live seasons periodical 

 determinations have been made of the amount of nitrate present in 

 soils under varying treatments. When these results are set out it is 

 found that the rate of accumulation of nitrates is usually rapid in 

 spring, falls off in summer, rises in autumn, and falls again in winter : 

 thus two maxima occur: one in spring and the other in autumn, while 

 the minima occur in summer and winter. Unfortunately, however, 

 the amount of nitrate in the soil at any time only represents the 

 balance of gains over losses and cannot be taken offhand as a 

 measure of the rate of production of nitrates, the quantity that is 

 really wanted. For some time we could see no way of getting 

 over the difficulty, but a simple solution was ultimately found. It 

 is evident that if the curves showing the amount of some other 

 substance produced in the same way as the nitrate but lost in a 

 different way are of the same general shape as the nitrate curves 

 then the shape is due mainly to the production factors ; if on 

 the other hand the two sets of curves are different in shape then 

 the loss factors control the situation. The carbon dioxide in the 

 soil air satisfies these requirements : it is produced like nitrates 



