THE PHYSICO-CHEMICAL INVESTIGATION OF SOILS. 337 



suits thus obtained are seen on all hands : for which reason, to 

 save space, they have not been introduced into this volume. It 

 seems at first sight that the same method should serve admi- 

 rably to determine the manure-requirements of soils under con- 

 trolled conditions. 



It must, however, be remembered that the field conditions as 

 regards subsoil, evaporation, ascent of moisture from below, 

 penetration and spread of roots, etc., in other words, all the 

 physical conditions so vitally concerned in crop production, 

 except the temperature and moisture-condition of the soil, are 

 wholly left out of consideration in this method. Hence the 

 application of the results so obtained to actual field conditions 

 can only be made with great caution, and are often widely dis- 

 crepant with actual experience. 



The method has of late been carried to an extreme by the U. S. 

 Bureau of Soils in the proposition to supplant the large soil-pots here- 

 tofore used by small paraffined wire-cloth baskets, 3X3 inches in size, 

 in which the soil to be tested is sown with seeds which are allowed to 

 develop only for three to five weeks; it being claimed thnt the devel- 

 opment occurring during that time is quite sufficient to indicate what 

 will be the ultimate outcome in crop production. But practical ex- 

 perience has long ago demonstrated that these early stages of growth 

 cannot be relied upon to show the crop results to be expected. Yet 

 if this minute scale of pot-culture should, on further test, prove to give 

 truthful forecasts even in a mere majority of cases, the facility with 

 which it may be carried out will entitle it to favorable consideration. 

 A great deal more proof is needed on this point than the confident 

 claims of the Bureau indicate. 



CHEMICAL TESTS OF IMMEDIATE PRODUCTIVENESS. 



Testing chemical soil-character by crop analysis. Another 

 method for the determination of immediate soil requirements 

 has been elaborated by E. Godlewski. 1 The principle upon 

 which this method rests is that plants growing in a soil defi- 

 cient in available plant-food of any one kind will in their ash 

 show a corresponding deficiency, or at least a minimum pro- 

 portion of the same ; and that in many cases, the nature of the 



1 Zeitschr. Landw. Vers. Oesterr., 1901. 

 22 



