194 ANNUAL, REPORT OF THE Off. Doc. 



Agricultural investigations have, in the search for methods useful 

 in guiding fertilizer practice, turned to the chemical analysis of the 

 crop produced upon a given soil, and to direct trial of yields by 

 experimental use of different fertilizers on a small scale. 



In examining the composition of the plant as an indicator of the 

 soils' deficiencies, the results of analysis of different organs from 

 plants grown on soils deficient in particular ingredients, and from 

 plants grown on plats of the same land in whicb the deficiency has 

 been made good by fertilizers, are used. 



The results of analysis are expressed in the form of ratios exist- 

 ing between the three important fertilizer constituents present in 

 the dry matter of the particular plant part used. The quantity of 

 nitrogen is usually taken as 100. From such examinations, Atter- 

 burg, examining the seed, concluded that if the ratio of phosphoric 

 acid to nitrogen were less than 50 : 100, the maximum crop could 

 not be obtained, and if the ratio were less than 20 : 100, it might 

 be concluded that a serious deficiency of phosphoric acid existed. 

 Stahl-Schroder from similar studies fixed upon the ratio 30-40 : 100 

 and 20-30 : 100 as more nearly correct than those fixed by Atterburg. 

 Mr. H. H. Pingree,* late assistant chemist in my laboratory, made 

 a careful study of the oats crop grown on a number of our fer- 

 tilizer plats at the station, and obtained results similar to those just 

 mentioned. It is probable that this method of examination of a 

 soil's condition would require as a basis of judgment a careful an- 

 alysis of the crops contained from a series of fertilizer plats on the 

 soil in question. The trials of this method have not been sufficiently 

 numerous to permit a safe judgment as to its limitations. 



Another class of methods for testing present needs of the soil 

 involves a comparison of the crop yields obtained from the unfer- 

 tilized land, and from that treated with various fertilizer constituents 

 and combinations thereof. I will refer first to those methods of 

 this class, which are designed to be conducted on a small scale, and. 

 it may be, at some point remote from the farm under study. In such 

 case representative portions of the soil are packed into pots, the 

 latter being first provided with a layer of coarse material to insure 

 the proper drainage. The upper layers of the soil in some of the 

 pots receive the additions of fertilizer, and the weight of crops pro- 

 duced in the several pots is accurately determined. In such experi- 

 ments care is of course taken to preserve, so far as practicable, sim- 

 ilarity of conditions with respect to the manner in which the soil 

 is packed into the pots, the temperature and the moisture during 

 growth. Heretofore it has been customary to use rather large pots 

 and to grow the crop to maturity in order to gain the comparative 

 data. It is a common fault of such experiments, no matter how 

 carefully conducted, that they do not exactly reproduce the tem- 

 perature, moisture and aeration conditions that influence the crop 

 grown on the undisturbed soil, and it is well known that each of 

 these conditions is an important factor in determining crop growth. 

 No matter how carefully conducted such experiments may be, it is 

 clear that they are of value as preliminary trials suggesting prob- 

 able needs of the lands rather than as conclusively showing both the 

 kind and the proportion in which the several fertilizers may be re- 

 quired. 



•See Report of the Pennsylvania Experiment Station of 1905-6, pp. 43-53. 



