ON ACCUMULATION OF NITRATES 85 



to be much more active in the slag plots than in the untreated. There 

 is a distinctly greater accumulation of nitrate during the periods 

 May 5th to 10th, May 31st to June 8th, July 5th to 17th, August 4th 

 and August 23rd to September 7th. Reference to Fig. 19 shows that 

 these periods roughly correspond to those periods at Horndon during 

 which there is a much greater accumulation of nitrate in the slag 

 plots, and with two exceptions, viz., May 31st to June 8th, and 

 August 23rd to September 7th, these dates hold good for Martin's 

 Hearne. On June 8th samples were not taken from Martin's Hearne, 

 so this exception is easily accounted for. The figures for this centre 

 for August 23rd to September 7th are curious. There is an accumula- 

 tion on both the treated and untreated plots, but it is greater on the 

 untreated than on the slag plot. Reference to Fig. 17 shows that 

 the same result was obtained from the pots, and that at this period, 

 and only at this period, did the nitrate in the untreated pot accumu- 

 late to an extent at all comparable with the slag pot. This result in 

 the field would seem to lend some weight to the suggestion that at 

 this period of the season the soil on the untreated plot has been able 

 to furnish sufficient phosphoric acid to meet the requirements of those 

 organisms engaged in the production of nitrates. 



These results are not in accordance with the conclusions come to 

 by Russell (25). As the result of his work on the "Nitrate Content of 

 Arable Soils," he says: "that only in one year (1911) was there any 

 evidence of the organisms responsible for nitrification being retarded 

 by a deficiency of phosphates and potash." It must be noted, however, 

 that the soil even on the untreated plot of Broadbaulk Field contains 

 considerably more phosphoric acid (-114 %) than the soils at Horndon, 

 Martin's Hearne, or Lambourne End. 



It is of interest to note that at Martin's Hearne and Lambourne 

 End periods of high nitrate accumulation coincide as a rule with 

 high moisture content of the soil, whilst at Horndon they coincide 

 with periods of low moisture content. At Martin's Hearne and at 

 Lambourne End the periods of high nitrate accumulation on the 

 slag and untreated plots occur as a rule at the same time (Figs. 21 

 and 22). 



At Horndon, on the other hand, periods of high nitrate accumula- 

 tion on the untreated plot follow, about a week later, similar periods 

 on the slag plot. This difference might possibly be due to some 

 influence the crop may have on nitrate production, but Russell (25), 

 when investigating this subject, was unable to secure any definite 

 data supporting such a contention. 



