CAPABILITY SUBCLASSES 



Subclasses are groups of capability units within classes that have the same 

 kinds of dominant limitations for agricultural use as result of soil and 

 climate. Some soils are subject to erosion if they are not protected, while 

 others are naturally wet and must be drained if crops are to be grown. Some 

 soils are shallow or droughty, or have other soil deficiencies. Still other 

 soils occur in areas where climate limits their use. The four kinds of limi- 

 tations recognized at the subclass level are: risks of erosion, designated 

 by the symbol (e) ; wetness, drainage, or overflow (w) ; root-zone limitations 

 (s) ; and climatic limitations (c) , The class and subclass provide the map 

 user information about both the degree and kind of limitation. Subclasses 

 are not recognized in Capability Class I. 



Subclass (e) erosion is made up of soils where the susceptibility to eros- 

 ion is the dominant problem or hazard in their use. Erosion susceptibility 

 and past erosion damage are the major soil factors for placing soils in 

 this subclass. 



Subclass (w) excess water is made up of soils where excess water is the 

 dominant hazard or limitation in their use. Poor soil drainage, wetness, 

 high water table, and overflow are the criteria for determining which soils 

 belong in this subclass. 



Subclass (s) soil limitations in the root zone is made up of soils where 

 root-zone limitations are the dominant hazard or limitation in their use. 

 These limitations are the results of such factors as shallow soils, stoni- 

 ness, low moisture-holding capacity, low fertility difficult to correct, 

 and salinity or alkalinity. 



Subclass (c) climatic limitation is made up of soils where the climate 

 (temperature and lack of moisture) is the only major hazard or limitation 

 in their use. 



Limitations imposed by erosion, excess water, shallow soils, stones, low 

 moisture-holding capacity, salinity or alkalinity can be .:cl::fied or par- 

 tially overcome and take precedence over climate in deter: ■.irii:;g subclasses. 

 The dominant kind of limitation or hazard to the use of the land determines 

 the assignment of capability units to the (e) , (w) , and (s) subclasses. 

 Capability units that have no limitation other than climate are assigned to 

 the (c) subclass. 



Where two kinds of limitation which can be modified or corrected are essen- 

 tially equal, the subclasses have the following priority; e, w, and s. 

 For example, we need to group a few soils in humid regions that have both 

 an erosion hazard and an excess water hazard; with them the e takes prece- 

 dence over the w; with soils having both an excess water limitation and a 

 root-zone limitation the w takes precedence over the s. In grouping soils 

 of subhumid and semiarid regions that have both an erosion hazard and a 

 climatic limitation, the e takes precedence over the c, and in grouping 

 soils with both root-zone limitations and climatic limitations the s takes 

 precedence over the c. 



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