642 IOWA DEPARTMENT OF AGRICULTURE 



the type or types of soil composing it. When this has been done the 

 different types are indicated on the map by different colors. Some excel- 

 lent colored soil survey maps have been recently published by the Illinois 

 Experiment Station in their Soil Reports Nos. 1 to 3 inclusive, and many 

 good maps showing less detail are to be found in the annual reports of 

 the Bureau of Soils. 



When the soil survey of a given county is completed, the map shows 

 all the soil types in the county and the exact area which each type covers. 

 It shows the part of the county w^herein the more common types of soil 

 are found and also the location of any peat, gumbo, sand or gravel, as 

 well as the areas which are rough and broken and those which are espe- 

 cially adapted to any particular crop. Because of these facts, a survey 

 is of great practical value to the man w^ho desires definite knowledge 

 regarding general cropping conditions or the fitness of a certain area or 

 soil type for a given crop. The latter point is nicely illustrated in the 

 production of sugar beets in Bremer county, Iowa. The growing of this 

 crop in that section of the state for a period of five years or more, has 

 shown that beet growing is much more profitable on certain soil types 

 than on others; in fact that the business is not successful on some of 

 the more sandy types. Clearly it is important that the owners of these 

 Bremer county soils or that prospective settlers w^ho may desire to grow 

 beets, should know the exact location of the "beet" soils. The survey now 

 in progress in that county will determine the exact acreage and location 

 of each soil type, and thus the "beet" lands can easily be found by any- 

 one who will consult the soil map which will be published later by the 

 Iowa Experiment Station and the Bureau of Soils. 



This is only one illustration of hundreds, or even thousands, that might 

 be given to show the practical helpfulness of a knowledge of soil types 

 and of their location based on a detail survey. 



While the field work of a survey is in progress, many samples of soil 

 representing each type are collected, in order that physical and chemical 

 analyses may be made. The physical analysis fixes the exact per cent of 

 clay, silt, sand, gravel, and stone in each type. These data aid the sur- 

 veyor to determine definitely the texture of the soil, and also the differ- 

 ence in textural conditions between the surface stratum and the under- 

 lying subsoil. Facts of this character often have an important bearing 

 upon drainage problems, and also upon the adaptation of soils to particular 

 crops. 



The chemical analysis gives the total supply of plant food in each 

 soil type and the organic matter content of each type, but the rate of 

 liberation is governed by many factors," some of which may be controlled 

 by the farmer while others are for the most part beyond his control. 

 We thus see that a soil survey gives an accurate invoice of the plant food 

 actually present in the different soil strata (samples for analyses are 

 usually taken to a depth of 40 inches and represent three strata; namely 

 the surface, subsurface, and subsoil). 



The facts stated above show that a soil survey, when completed, fur- 

 nishes information concerning: (1) The location and area of the different 



