SOILS FERTILIZED. 743 



principal mineral plant-food constituents are broughl into solution and made avail- 

 able to the plant. What concentration thesoil moisture actually possesses has beeu 

 determined with what maybe regarded as approximate accuracy. Two methods 

 have been devised for extracting the free solution actually existing in a soil, and 

 analyses of a number of such extracts obtained from several I oil of widely 



different origin and composition have yielded an average for potassium I K • of 27.3 

 parts and for phosphoric acid I l'« >, 8.5 parts per million of solution. 



" The approximate uniformity of the indh idual results make it appear improbable 

 that further accumulation of data would change these average figures materially, . . . 

 sine- practically all soils contain the same minerals and essentially the -aim- pro- 

 cessesare taking place in all of them it would follow thai aboul the same solution 

 should be expected in all soils, excepl in so far as changes were introduced by differ- 

 ences in absorptive powers of the solids, rates of movement of water, etc. Examina- 

 tions of a large number of soil-, many of which have been already published, estab- 

 lished empirically that these considerations are justified. . . . 



" (4 t The concent rat inn of the soil -oh it ion, with respect to the principal mineral 

 plant-food nutrients, is sufficient for thegrowthand development of crops. And, 

 further, the magnitude of the concentrations is the same for practically all soils." 



A review of studies of the effect of surfaces in modifying not only in intensity but 

 even in kind the reactions taking place in solutions in contact with them and of the 

 nature and effect >f the organic matter of the -oil lead- to the general conclusion that 

 •'the development of a modern soil chemist ry is dependent upon a study of the 

 chemical changes induced by surface contact, and upon a study of the proportions of 

 the water soluble organic as well as inorganic matter of the soil." 



A comparison of the results obtained by the method of cultures in paraf- 

 fined wire pots with field results on the same soil, II. J. Wheeler, I'.. E. 

 Brown, and J. ('. Bogenson [Rhodi Island Sta. Bui. 109, />/>. 18-44, pis. 

 This is an account of a series of experiments made in cooperation with the Bureau 

 of Soils of this Department to test the value of the paraffined wire pot method of 

 testing the fertility of soils devised by the Bureau l I-'.. S. R., hi, p. 650; 17, p. 227). 

 Seventeen series of experiments with soil- from plats which have been under experi- 

 ment at the station for several years past and from a farm on the Kingston Plain 

 are reported. These include tests of various combinations of fertilizers, barnyard 

 manure, green manure, lime, etc., on corn, wheat, crimson clover, alfalfa, and lettuce, 

 the effect of continuous planting on the same pots with and without renewal of the 

 manures, fertilizers, etc., being studied. 



The results are thus summarized: 



"Tests by the method of paraffined wire pots of a soil which, under the existing 

 field conditions was so poor as to produce Indian corn only 5^ in. high during the 

 entire season, revealed manurial requirements in accord with those shown by plant 

 tests in another part of the same held. This was true both before and after liming. 

 Marked benefits from liming and from the use of Btable manures, similar to those 

 observed in the field, were also obtained. 



" It was shown by this method that ' denitrification,' or a destruction of nitrates, 

 very likely resulted where the stable manure and nitrates were used together. 

 There is no evidence to show that this denitrification was necessarily any more pro- 

 nounced than it would have been in ordinary pot-. 



"The use of all three mineral manures, in addition to lime, also depressed the 

 yield. This effect was apparently lessened by the presence of horse manure. Upon 

 the third replanting this ill effect disappeared. It seems probable that upon a similar 

 soil, if limed, the quantities of the manurial substances should be reduced in making 

 such tests. 



•' Benefit from adding green manure- was shown in the pots, as i> also the case in 

 the field. 



