APPENDIX 3 



THE LAND-CAPABILITY CLASSIFICATION 



The standard soil-survey map shows the different kinds of soil that are sig- 

 nificant and their location in relation to other features of the landscape. 

 These maps are intended to meet the needs of users with widely different 

 problems and, therefore, contain considerable detail to show important basic 

 soil differences. 



The information on the soil map must be explained in a way that has meaning 

 to the user. These explanations are called interpretations. The capability 

 classification is one of a number of interpretive groupings made primarily 

 for agricultural purposes. As with all interpretive groupings the capabil- 

 ity classification begins with the individual soil-mapping units, which 

 are building stones of the system. In this classification the arable soils 

 are grouped according to their potentialities and limitations for sustained 

 production of the common cultivated crops that do not require specialized 

 site conditioning or site treatment. Nonarable soils (soils unsuitable for 

 longtime sustained use for cultivated crops) are grouped according to their 

 potentialities and limitations for the production of permanent vegetation 

 and according to their risks of soil damage if mismanaged. 



The individual mapping units on soil maps show the location and extent of 

 the different kinds of soil. Mapping units permit making the greatest num- 

 ber of precise statements about the individual soils and predictions about 

 their use and management. The capability grouping of soils is designed to 

 (1) help landowners and others use and interpret the soil maps, (2) intro- 

 duce users to the detail of the soil map itself, and (3) make possible 

 broad generalizations based on soil potentialities, limitations in use, 

 and management problems. 



The capability classification provides three major categoriess (1) Capa- 

 bility unit, (2) capability subclass, and (3) capability class. The first 

 category is the capability unit, which is a grouping of soils that have 

 about the same influence on production and responses to systems of manage- 

 ment of common cultivated crops and pasture plants. Soils in any one 

 capability unit are adapted to the same kiiuis of common cultivated and 

 pasture plants and require similar alternative systems of management for 

 these crops. Longtime estimated yields of adapted crops for individual 

 soils within the unit under comparable management do not vary more than 

 25 percent. 



The second category in the classification is the subclass. This is a 

 grouping of capability units having similar kinds of limitations and haz- 

 ards. Four kinds of limitations or hazards are recognized? (1) ejrosion 

 hazard, (2) wetness, (3) root zone limitations, and (4-) climate. 



The third and broadest category in the capability classification places 

 all the soils in eight capability classes. The risks of soil damage or 

 limitations in use become progressively greater from Class I to Class VIII, 



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