FERTILIZERS, ROTATIONS FOR COTTON 97 



possible only when an adequate supply of organic matter 

 is maintained in the soil. No greater error can be made 

 by the cotton-grower than that of depending upon commer- 

 cial fertilizers to overcome the ill effects produced by a 

 deficiency of vegetable matter, poor tillage, and lack of 

 drainage. In this connection it is well to remember, (1) 

 that the primary function of commercial fertihzers is to 

 add plant-food to the soil, and (2) that plant-food is only 

 one of the several factors essential to the profitable produc- 

 tion of crops. 



The abiUty of the crop to obtain plant-food and moisture 

 from the soil, and also profitably to^utilize the nutrients 

 supplied in fertihzers is determined largely by the physical 

 condition of the soil, and the solvent, power of the soil 

 water. Decaying vegetable matter produces that physical 

 condition necessary for \he proper aeration of the soil and 

 also suppKes by-products which, > when dissolved in the 

 soil water, greatly inc/ease its solvent power for plant- 

 food. As a result of these effects, the organic matter de- 

 creases the need for fertilizers in the production of cotton 

 on soils that are well supplied with the mineral plant- 

 foods and renders much more effective the mineral fer- 

 tihzers that are essential on soils in which the mineral 

 plant-food naturally is somewhat deficient. The most 

 important source of organic matter for soils in the cotton- 

 belt is that of green-manures. 



109. Suitable crops for green-manure. — Crops suit- 

 able for use as green-manures in the cotton-belt are of two 

 classes; legumes and non-legumes. Of the first class, the 

 cowpea, soy bean, crimson clover, bur clover, vetch, 

 melilotus, and the velvet bean are most important. Be- 

 longing to the second class are rye, oats, wheat, barley, 

 and millet. 



