]'y2 l<'()(»I) \-()\l I^.ANTS. 



AVhon tlie work wns hcnuii all the soils were given a 

 nix'i'al Ileal iiiciit of lime in the form of ground lime- 

 stone and with the exception of one series which does 

 not enter into tiiis discussion, all have received annual 

 dressings of acid i)hosphate and potassium chloride at 

 the rate of (540 j)onnds and 320 pounds per acre, respec- 

 tively. Thus nitrogen is made the limiting factor inso- 

 far as human control can provide. Various combina- 

 tions of manure and fertilizer were arranged, but it is 

 sufficient to rejjoi't here only on the four nitrogenous 

 materials mentioned in the title. 



One series recei\ed the phosphoric acid and potash, 

 l)ut no nitrogen, in order that it might be used as a 

 check. Thus if a certain amomit of nitrogen is recovered 

 in the crop from the nitrogen-treated cylinder, and it is 

 desired to calculate the percentage of the applied nitro- 

 gen that was recovered, it is necessary first to deduct 

 from the total amount of nitrogen recovered in the crop, 

 the amount recovered from the check cylinder, and thus 

 account for the soil nitrogen that the crop used. 



It is at once obvious that this cannot be an absolutely 

 correct method of determining the percentage recovered, 

 since in those cylinders to which nitrogenous fertilizers 

 have been ap])lied, the plant will make a quicker start 

 and the roots go farther in search of the nitrogenous 

 materials of the soil than in the check cylinders where 

 there is a pronounced deficiency of available nitrogen, 

 and thus the check fails to be a tnie check. In this way 

 it ha])pens that the recovery may apparently be more 

 than 100 per cent, as shown in Series 8B, for the years 

 liM)l and 1 !)!(). However, there appears to be no way of 

 overcoming this error so long as the w^ork is carried out 

 in the natural soil and if one starts with an artificial 

 soil, other and more serious difficulties arise. 



In this woi'k no effort has been made to analyze the 

 roots, since it would be well-nigh impossible to do this 

 correctl)', and even if it could be done the same error 

 would be intr(Mlucrd. The roots and stubble are left 

 just as undei' lield conditions so that the residual effects 

 of these mav l)e observed. 



