CHAPTER IV 



Fertilizers 



By no method known to chemical science is it 

 possible to determine the crop-producing capacity 

 of a soil or to ascertain what should be applied in 

 order to increase the yield. Analysis will show 

 the total amounts of each of the elements neces- 

 sary to plant growth present in a soil, but the 

 plant alone can discriminate between the available 

 and the non-available. Those that are available as 

 plant foods are generally spoken of as soluble in 

 water and those not available as insoluble. The 

 insoluble ingredients act as a reserve and are slowly 

 made available for the use of plants by the action 

 of carbonic acid. The determination of what is 

 lacking in any soil must be made by the applica- 

 tion of various kinds and quantities of fertilizers, 

 and the results recorded by the growth of plants. 



Natural Fertility of Soils. — The natural fertility 

 of most soils is sufficient for the production of from 

 20 to 200 crops if it be rendered available. Fertili- 

 zers are used on soils of this character to insure the 

 production of a crop and also to aid in the trans- 

 formation of the latent soil fertility. The libera- 

 tion of the plant food locked up in the soil can 

 generally be greatly promoted by drainage, the 

 addition of humus, special tillage, or the applica- 

 tion of some disintegrating material such as lime. 



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