SOIL -DEPLETING, SOIL -CONSERVING, AND 

 SOIL-BUILDING CROPS 



By A. J. Pieters, 2 principal agronomist, Section of Agronomy and Range Manage- 

 ment, Division of Conservation Operations, Soil Conservation Service 



The Soil Conservation Service is vitally interested in conserving the 

 soil by using the land properly. Some crops are said to be "soil deplet- 

 ing," some "soil conserving," and others "soil building." These crops 

 differ in their effect on the conservation of soil and water. It seems 

 desirable that the meaning of these terms and the reasons why some 

 crops are soil-depleting, some soil-conserving, and others soil-building 

 should be well understood. 



The terms "soil-depleting," "soil-conserving," and "soil-building 

 crops" must not be confused with soil-depleting, soil-conserving, and 

 soil-building practices. A soil may be depleted by a bad practice 

 though no crops are grown. Soil-conserving and soil-building prac- 

 tices involve the application of lime and fertilizers, the practice of 

 rotations, and the use of other measures that go beyond the mere use 

 of certain crops. 



There are many kinds of soils, ranging all the way from light sands 

 to silts and heavy clays. Soils differ in texture as well as in the kinds 

 and quantities of plant food they contain. For 

 Soil present purposes we may say that a soil is an aggre- 



gation of minerals derived from the decay of rocks, 

 plus organic matter. Surface soils vary from a few inches to a con- 

 siderable depth. Subsoils differ from surface soils in various ways but 

 particularly in having a lower organic-matter content. 



The organic matter is the home of micro-organisms, whose activity 

 makes plant food available to crop plants. Mention may be made of 

 Azotobacter, forms which are able to use atmospheric 

 Organic Mat- nitrogen, provided energy material is available. This 

 ter In Soil they find in the organic matter. Organic matter also 



influences the texture of the soil. It is, therefore, 

 quite as important a part of the soil as the minerals. 



Plants need a variety of minerals for nutrition, but the ones that 

 commonly need to be considered in agricultural practice are lime, 

 phosphorus, potash, and occasionally magnesium. 

 Minerals In Under certain conditions elements such as manganese, 

 Soil boron, copper, iron, and zinc may be added to soils to 



advantage, and in rare cases, some of the less-common 

 minerals. Plants also need nitrogen, but that does not come from the 

 decomposed rock. A soil may be depleted with respect to its mineral 

 plant food or with respect to its organic -matter content or both. Let 

 us define a soil-depleting crop and consider the loss of minerals and 

 of organic matter. 



i Contribution from Soil Conservation Service and Bureau of Plant Industry. 



2 Formerly principal agronomist, Division of Forage Crops and Diseases, Bureau of Plant Industry. 



Issued September 1938 



