30 EXPERIMENT STATION RECORD. 



The author concludes from the results obtained that the ultimate chemical analy- 

 sis (by fusion) of a soil "affords absolutely no reliable basis for a classification." 



"The solubility of the essential plant foods in strong acids is shown to afford a 

 grouping and an arrangement within the groups that is about as valuable as the results 

 based upon the physical properties alone. The solubility in weak hydrochloric 

 acid affords about as satisfactory a grouping as either of the above methods. The 

 systematic classification of these soils upon the combined influences of their physical 

 and chemical properties is as yet impossible. There are evidently undetermined 

 factors whose influence is great enough to vitiate this classification." 



The results indicate that these soils are most in need of lime or lime and organic 

 matter. "Phosphoric acid is probably the substance which, after lime, is indicated 

 as being most needed." 



' ' In the order of economic importance the next need of our soils is nitrogen. 

 While we have no data upon the actual nitrogen content of these soils, some infor- 

 mation' upon this point may be gained by the amount of volatile (organic) mat- 

 ter which they contain and Avhich approximately determines their nitrogen 

 supply. . . . 



"From the results of the chemical analysis it is evident that the addition of potash 

 is the least needed of the several plant foods. In all the soils it is present in great 

 quantities. Its solubility in the two solvents, concentrated and fifth-normal hydro- 

 chloric acid, is indicative of its presence largely in an available form in all but the 

 light sandy soils of the State." 



A chemical study of the phosphoric acid and potash contents of the wheat 

 soils of Broadbalk field, Rothamsted, B. Dyer {Froc. Roy. Soc. [London], 68 

 {1901), No. 44^, PP- 11-14)- — Determinations of phosphoric acid and potash soluble 

 in strong hydrochloric acid and in 1 per cent citric acid in samples of soils from the 

 first, second, and third 9 in. of the soil of 12 plats, manured in different ways and 

 unmanured, that had been cultivated in wheat for 50 years consecutively, are 

 reported. (See also E. S. R., 10, p. 933. ) Examinations of samples of the same soils 

 collected in 1865 and 1881 are also reported. 



"The difference between the total percentages of phosphoric acid in different soils, 

 unmanured and variously manured, corresponds fairly well with their history, but in 

 the absence of a knowledge of such history these differences would not suffice to 

 give any indication of the profound differences known to exist in the phosphatic 

 condition and fertility of the soils. The relative proportions of citric acid soluble 

 phosjihoric acid, however, appear to afford a striking index to the relative phosphatic 

 fertility of the soils." 



The superiority of the citric acid method for determining the phosphoric acid 

 requirements of a soil was more strikingly shown in case of the subsoils than of the 

 surface soils. In the surface soils the average ratio of the total phosphoric acid in 

 plats which had received phosphatic fertilizers to that in plats receiving no phos- 

 phates for 50 years was 1.65:1; of citric acid soluble phosphoric acid, 5.46:1. The 

 results obtained indicate that a soil containing as low as 0.01 per (*nt of citric acid 

 soluble phosphoric acid in the surface soil needs phosphatic fertilizer, while that 

 containing as much as 0.03 per cent is in no immediate necessity of such fertilizing. 

 The results generally indicate also that the greater proportion of the uneonsumed 

 phosphoric acid accumulates in the first 9 in. of soil. In case of barnyard manure 

 and of superphosphates accompanied by potash, soda, and magnesia salts, the fer- 

 tilizing constituents were diffused to a considerable extent throughout the second 

 and even the third 9 in. 



"Strong hydrochloric acid as a solvent for potash in soil analysis is shown to be 

 practically useless as a gauge of potash fertility where there is an abundance of total 

 potash in mineral combination, as silicates, etc. . . . The results obtained by 

 citric acid, however, are strikingly instructive and consistent. . . . The ratio of the 



