100 Lime Reqi/in'mriifs of Crrfaijt Snifs 



this paper, where it is shown that 0-(5 per cent, constitutes the critical 

 dressing capable of producing the maximum first crop, while 0-8 per 

 cent, is too high for this soil. 



Finally, the results are of interest in connection with the question 

 of acidity as indicated by the suggested bicarbonate method. Although 

 maximum growth of the crop is produced by an application of 0-.36 per 

 cent., the preceding deviation in the curve might fairly be taken as an 

 indication that this amount is actually in excess of the re(|uirements. 

 If therefore the two linear portions of the curve - the initi.'d and the 

 final — be continued as is shown by the dotted lines, it will be found 

 that the point of intersection occurs above the point already indicated 

 as being the acidity by the bicarbonate method, namely, equal to 

 0-260 per cent, calcium carbonate. W'itliout wishing to inqily tluil 

 with all soils the crop growth is directly ii\ inverse ratio to the aciflity 

 of the soil, a close agreement appears to occur in this case between the 

 lime requirement as shown by the bicarbonate method and the physio- 

 logical gauge set by the plant. 



The Relation between Soil Reaction and Bacterial Activili/. 



In discussing the necessity of maintaining an adequate supply of 

 base in cultivated soils, it is generally recognised that the presence of 

 carbonate is requisite for the maximum activity of nitrifying and 

 nitrogen-fixing organisms, but little attention is paid to the preceding 

 putrefactive or amnionification process. The work of Russell (■!()) and 

 others shows that the amount of nitrate formed in field soils is strictly 

 dependent on this preceding change, in fact, the ammonia formed is 

 nitrified almost as soon as produced, hence the ammonia content of 

 normal soils is invariably low. 



In our own work with the Craibstone soil (which is free from car- 

 bonate) the amount of free ammonia is kept at a low level by continuous 

 nitrification, while even with the Woburn soil the reserves derived from 

 the fertilisers applied are subject to a steady change into nitrates. It 

 appeared of interest, therefore, to ascertain how far a supply of calcium 

 carbonate would affect each of these processes in the Craibstone soil, 

 and two experiments with this end in view were made. It was obviously 

 necessary for the demonstration of increased ammonification that nitri- 

 fication should be eliminated and this we accomplished by treating the 

 soils with toluene. Equal lots of 600 grms. of the moist soil were filled 

 into bottles and these were divided into three sets. Of these the .soil 



