THIRTEENTH ANNUAL YEAR BOOK— PART XII 643 



soil types; (2) the physical or mechanical composition of the soil; and 

 (3) the total supply of plant food in each type of soil. 



The statement has been made that the facts secured by a soil survey 

 are often helpful from the standpoint of the adaptation of soils to crops, 

 drainage problems, etc. This is true, but we must not lose sight of the 

 fact that a survey is primarily valuable because it shows what our soil 

 problems are, where they exist, and the extent of country affected. 



This means, of course, that additional soil studies must be undertaken, 

 if these problems are to be solved successfully. This point deserves 

 emphasis. We are certain that it would be a grave mistake for any state 

 or federal agency to base its soil studies in the field wholly upon a soil 

 survey. This is true, because a landowner can not get even approximately 

 the full measure of benefit from a survey unless the facts contained 

 therein are interpreted in terms of his local soil problems. For instance, 

 a survey report indicates on the map that 60 per cent of a farmer's land 

 is brown silt loam, and the remaining 40 per cent is black clay loam. 

 Of what value is this information? The farmer has probably determined 

 from observation that certain crops commonly grown in the locality, do 

 better on one type than on the other, or that a certain system of soil 

 management already in general use seems to be especially adapted to one 

 of these soil types, but not to the other. The chances are that these 

 observations, based on purely local conditions, would have been made had 

 no survey been carried on. 



The point of vital importance to the farmer is this: Are the crops 

 which I am growing the most profitable for the types of soil on my farm; 

 are my rotations and my systems of soil management of such a character 

 as to enable me to secure maximum crop yields? 



Now a soil survey does not answer these questions, nor solve the prob- 

 lems involved; it merely indicates the problems and suggests certain 

 lines of investigations for the different types of soil. Again, the soil 

 survey report carries the information that the brown silt loam, for in- 

 stance, which is found in the county as indicated on the map, contains 

 per acre in the surface soil, let us say, 3,000 pounds total nitrogen, 700 

 pounds total phosphorus, and 24,000 pounds total potassium. What use 

 can the farmer make of these data? It must be confessed that they will 

 not help him very much with his fertility problems unless they are cor- 

 related with data from some field experiments. 



However, if a soil survey is followed by a series of field experiments 

 to determine crop adaptations, suitable rotations, and the absolute needs 

 of the various types of soils for different fertilizing materials, such as 

 manure, limestone, phosphorus, etc., then the survey and the field experi- 

 ments supplement each other and each is made a potent factor for soil 

 improvement. The survey indicates a probable shortage of some essential 

 plant food constituent, the presence of acid, or the existence of some 

 unfavorable physical condition of the soil. The field investigations, based 

 in part at least on the indications of_the survey, are carried on in such 

 a way as to prove, if possible, that certain methods of soil management 

 or the application of one or more fertilizers will increase crop yields and 

 tend to build up the productive capacity of the soil. 



