Failure to maintain a high degree of efficiency of the soil for any 

 particular crop is very often seen in the misadaptation of soil mate- 

 rial or the use of a soil series which does not function properly for 

 the crop grown. As an illustration, it is not to be expected that 

 soils of the Portsmouth, Volusia, and Susquehanna series will pro- 

 duce under normal conditions of cultivation satisfactory crops of 

 wheat, and with other series there are degrees of adaptation from 

 which it is possible to eliminate many soils from consideration for 

 commercial wheat production. 



In the matter of class of material, also, the sands and up to and 

 including the fine sandy loams are generally unsuited to wheat pro- 

 duction, while the heavier members of the series may be admirably 

 adapted to this crop. This illustration holds for most soils and for 

 most crops, and it is not to be expected that equal success will be 

 attained by the indiscriminate use of soils for any or all crops. 



The structure of a soil and subsoil and often of the deep subsoil 

 affect the adaptation to crops without imparting to the soil sample 

 evidences of the unfavorable conditions which exist. Such condi- 

 tions can only be determined by a field examination. 



In many instances the depth to the subsoil determines the charac- 

 ter, grade, or yield of crops, particularly in highly specialized indus- 

 tries. For example, in the production of the Sumatra leaf tobacco 

 on the Norfolk fine sandy loam in Florida, a soil of medium depth 

 of 6 or 8 inches gives by far the better quality, and where the sub- 

 soil is found closer to the surface or considerably deeper equally 

 good results are not to be expected. 



Topography and elevation play an important part in the adapta- 

 tion of certain crops, sometimes limiting sharply the kinds and at 

 other times the quality or the yield. 



The color of the soil is often a safe guide in the adaptation of soils, 

 indicating as it does not only material differences in constitution, 

 but also the general nature of the processes taking place in the soil. 



The presence of concretionary formations, either as gravel or as 

 more or less continuous layers of hardpan, influence the adaptation 

 and frequently the yield, acting in such a way as to leave no sensible 

 effect upon the sample submitted for examination, and requiring a 

 field investigation rather than a laboratory analysis. 



All of these subjects are treated in the soil survey reports and 

 adequate information is supplied for such areas as have been sur- 

 veyed, but where misadaptation of material owing to the presence of 

 any of thsse factors gives an insufficient crop, the results of labora- 

 tory investigations upon the sample, removed from its place in the 

 field and changed in its physical conditions through packing and 



[Cir. 26] 



