23 



II. " The Influence of Soil Cotiditious on the Decomposition of 

 Organic Matter in the Soil.'" E. J. Russell and A. 

 Appleyard. Journal of Agricultural Science, 191 7. 8, 

 385-417- 



The changes in bacterial numbers and in nitrate content of the soil 

 and in carbon dioxide content of the soil air were determined at frequent 

 and regular intervals during several seasons on five different plots of 

 land; and the results are set out on curves. 



There is sufficient resemblance between the curves for bacterial 

 numbers^, carbon dioxide (except for a period on cropped land), and 

 nitrate content to justify the conclusion that they are all related. 



The curve for nitrates, however, is always behind that for bacterial 

 numbers, the lag amounting to two or three weeks. Assuming that 

 the curves are connected, this would indicate two stages in nitrate 

 production : one related to the bacterial numbers, the other not. 

 Evidence is brought against the view that the stages are simply 

 ammonia production and then nitrate production ; the division has 

 apparently to be carried further back and ammonia production to 

 be divided into two stages. 



The biochemical decompositions in the soil are determined in the 

 first instance by the temperature and do not proceed to any notable 

 extent below 5° C. 



As soon as the temperature rises in spring, action takes place 

 rapidly. But it soon slows down and other factors begin to operate. 



Moisture is one of them. Action came to a minimum in June, 

 when the moisture fell to 10 per cent, by weight of the unmanured 

 soil and 15 per cent, by weight of the dunged soil, or 16 and 22 parts 

 respectively by volume, assuming there was no contraction. 



Rainfall is an even more important factor, a shower of rain having 

 a notable effect in starting the decompositions. It seems probable 

 that the dissolved oxygen plays an important part here. 



The growing crop exerts a depressing effect, though whether by 

 taking up the dissolved oxygen, giving out carbon dioxide, or some 

 other action is not clear. 



The fluctuations in bacterial numbers are not wholly explicable as 

 functions of the temperature and moisture content. Some of the rises 

 and falls are of the kind obtained during the investigations on partial 

 sterilisation ; further work on this problem is in hand in our labora- 

 tories. 



III. " Dissolved Oxygen in Rain Water. Eric Hannaford 

 Richards. Journal of Agricultural Science, 1917. 8, 

 331-337- 



Rain water was collected in a special form of apparatus, and the 

 amount of dissolved oxygen was determined by Winkler's method on 

 each occasion when 0.3 inches or more fell — this being the lowest rain- 

 fall that gave sufficient liquid for the analysis. During autumn, 

 winter and spring, when the temperature was below 15° C, the rain 

 was practically saturated with oxygen, the quantities found being on 

 an average 93 per cent, of Dittmar's complete saturation values for 

 distilled water. Rain collected in summer, however, was less saturated, 

 the amount of oxygen being 85 per cent, of the full saturation value. 

 The difference was carefully examined and found to be real ; it is 



