22 



In almost all the soils examined the accumulation of nitrate 

 took place most rapidly in late spring or early summer. After this 

 there was usually little if any gain, and frequently a loss. In the 

 hot dry autumn of 1911, however, and again in 1913, the accumula- 

 tion continued in some of the soils right on till September. 



During the winter loss of nitrate took place. This was more 

 marked in the wet winter of 1911 — 1912 than in the drier winter of 

 1908—1909. 



The fluctuations in nitrate content are more marked on loams 

 than on clays or sands. Clays lose less of their nitrates in winter, 

 but, on the other hand, they accumulate smaller amounts in June 

 and July. Sands lose much of their nitrates in winter and do not 

 accumulate very large amounts in summer. It appears that the 

 main loss in winter is due to leaching and not to denitrification. 



On comparing the nitrate content of cropped and fallow land it 

 is found that during late summer and early autumn the fallow land 

 is the richer, even after allowing for the nitrate taken up by the 

 crop. The question arises, whether the growth of a crop exerts any 

 depressing effect on the rate of nitrate production in the soil. This 

 is under further investigation. 



The rapid rise in nitrate content in spring does not usually set 

 in immediately the warm weather begins ; there is a longer or 

 shorter lag. There are indications of greater bacterial activity in 

 early summer than later on, a phenomenon readily explicable on our 

 view that the soil population is complex and includes organisms 

 which are detrimental to the activity of bacteria, but which are, on 

 the whole, more readily put out of action. 



The supply of nitrate to the plant is known to be a factor of 

 prime importance in plant growth. Similarly it is found that the 

 factors which determine the accumulation of nitrates in the soil also 

 play a great part in determining the amount of crop production. 

 Thus heavy winter rainfall, which washes out nitrates, tends to 

 reduce crop growth ; on the other hand, hot dry summers, succeeded 

 by dry winters, are shown to be favourable to nitrate accumulation, 

 and therefore to crop growth. 



XXIII. The Effect of Climate and Weather on the So?7." 

 E. J. Russell. Journal of the Royal Agricultural 

 Society, 1914. 74, 1—21. 



Climate is shown to play a considerable part in determining the 

 character of a soil, affecting not only the mineral particles, but also 

 the nature and amount of the organic matter. Where definite cli- 

 matic zones exist they are usually found associated with definite soil 

 zones. Instances are quoted from North America and from 

 Russia. 



The effects of weather are of more direct interest to the culti- 

 vator, and involve the texture of the soil and also the stores of 

 nitrates. Using the data collected in the preceding paper it is shown 

 how a considerable saving may be effected by sowing a green crop 

 at the end of a dry summer or autumn, which shall take up the 

 nitrates and save them from being washed away. When the crop is 

 ploughed in or folded, the nitrogen is returned to the soil in a form 

 in which it is not readily lost. 



