SOILS FERTILIZERS. 119 



"The occurrence of ru:nif:anese concretions, the largest in size of which being 

 some depth below the surface, and deposited in the lower levels in the alluvial 

 sheet but not in the sedimentary or residual soil, together with the sharp line of 

 stratification separating the alluvial from the residual strata, indicate that there 

 has been a submergence, during which time the deposition of the alluvial soil 

 and the accumulation of manganese concretions took place. Subsequent leaching 

 further accentuated the accumulation of the manganese in the lower places, 

 especially in basins or at the bases of long slopes. 



"The solubility in weak organic acids shows that the availability of the 

 manganese is relatively high and that manganese probably exists in the soil 

 moisture and in solution around the absorbing surfaces of roots in greater quan- 

 tities than any other element. Therefore it exists in just the condition to 

 exert its full physiological effects on plants. The physical properties of the 

 manganiferous soils are more nearly ideal than are those of rod soils. They 

 contain less clay, and more of the coarser particles. Consequently the circula- 

 tion of'air is greater in the manganese soil. 



" Nitrification and annuonification api>oar not to be inllufinced by the presence 

 of manganese in the soil. That the former has been found to take place more 

 advantageously in the manganese soil can probably be accounted for by the fact 

 that the circulation of air is less obstructed in this type." 



Modification of the method of mechanical soil analysis, C. C. Fletcher and 

 11. Bryan (U. »S'. iJrpt. Agr., Bur. trails Bui. 8), pp. 3-1 H, pis. 7).— This bulletin 

 describes the apparatus and methods used in making the mechanical analysis 

 of soils as at present carried out in the laboratoi-y of the Bureau of Soils. 



The most imr)ortant modification of previous methods is that for determining 

 the amount of clay. It was decidetl to abandon the final transfer of the clay 

 solution to the platinum dishes and to complete the evajwration Ib the enameled- 

 ware saucepans and to weigh the clay in them without transfer. Much smaller 

 enameled cups (about 300 cc. capacity and 180 gm, weight) were adopted for 

 convenience in weighing and to decrease the likelihood of the entry of dust. It 

 is stated that the method has the disadvantage of requiring a much heavier 

 balance, but the determinations are none the less accurate and a great saving in 

 time is effected. The method may be still further shortened in case of routine 

 analyses by abandoning altogether the direct determination of clay and obtain- 

 ir.g its percentage by difl'erenco. " The error thus introtluced is probably no 

 greater than that involved in the centrifugal (or other) separation of the clay 

 from the silt. The errors in both cases are generally within the limits of varia- 

 tion which may be expected between different samples of the same soil. 



" In 100 consecutive analyses taken at random from the recent files of the 

 Bureau of Soils the variations between the percentage of clay as directly de- 

 termined and those obtained by dilference range between and 2.28 per cent. 

 In 2 cases the variation is over 2 per cent ; in 3 cases, between 2 per cent and 

 1.5 per cent ; and in 6 cases between 1.5 per cent and 1 per cent. In all other 

 cases the variations were less than 1 per cent. 



" It is probable that in many cases the determination by difference is the 

 more accurate, as all errors due to access of dust or to loss of clay suspension 

 are thus avoided. Errors due to a not impossible change in the state of hydra- 

 tion of the clay are also eliminated. It is believed that in the vast majority of 

 cases the method of determining clay by difference will be accurate within 1 

 per cent, and no greater accuracy is necessary or even desirable for purposes 

 of soil classification. . . . The direct determination must, of course, be re- 

 tained for cases of special importance or where a check is necessary, and is 

 probably also desirable for students and for small laboratories where a me- 

 chanical analysis is only made occasionally." 



