SOIL SESSION. 133 



EXPERIMENTS WITH COMMERCIAL FERTILIZERS. \ 



(Prof. H. A. Huston, Chicago, 111.) 



The last speaker has reHeved me of the necessity of making any 

 extended explanation in regard to some of the principles involved in 

 the use of commercial plant foods. We may pass directly to our sub- 

 ject, and perhaps it may be helpful if we spend a few minutes in con- 

 sidering what the crops remove from the soil, using the wheat plant for 

 an example. 



A bundle of wheat as it leaves the binder, contains, in addition to a 

 variable amount of water, about 10 pounds of material. By a partic- 

 ularly fortunate provision of nature, the most of this material is de- 

 rived from air and water. \ye may make a rough separation by burn- 

 ing the bundle. Most of it passes off in the form of gases or smoke^ 

 and of the ingredients burned all, with one exception, to which we will 

 refer again, were derived from the air and water. There remains a 

 small quantity of material, commonly called ash, and while it is small, 

 both in bulk and weight, as compared with the whole bundle, being. 

 only about 3.5 per cent, or one-third, of a pound to the bundle, it i& 

 none the less important. There are nine substances present in this 

 ash, which are found to be needed by the plant ; two of them, chlorine and 

 soda, are, perhaps, of less vital importance to most plants, but the others 

 are surely essential to normal plant growth. The quantities of all of 

 these mineral ingredients in the bundle of wheat are shown in these 

 vials, in the form of familiar compounds. For our present purposes we 

 might set aside the silica, iron, magnesia, soda, sulphur and chlorine, 

 since every ordinary soil will furnish these in abundance, and they are 

 never applied as plant foods, and when present in fertilizer mixtures 

 no money value is attached to them. The same is true of lime, which 

 is never applied to land for the purpose of furnishing plant food, al- 

 though it is frequently used to great advantage in correcting acidity and 

 in improving the mechanical condition of heavy soils. Used alone, its 

 final effect is soil exhaustion. 



There remain two substances which are found in relatively large 

 quantities in the ash and are found in most soils in limited amounts 

 and unavailable forms. The first of these is phosphoric acid and the 

 second is potash. These constitute two of the three so-called essential 

 plant foods ; not because they are really more necessay than the others, 

 but because of the plant's demand for a large amount of them and be- 

 cause of the plant's difficulty in getting them from the relatively in- 

 soluble compounds in which these two substances occur in soils. 



