16 STATE BOARD OF AGRICULTURE. 



l)i'Opoi'tions in the eniiili. Thus silica, alone or in combination, makes 

 up one-fourth part of the matter forming the rock-ribbed earth. Lime 

 forms vast mountain chains, and is also found in every soil. 



On the other hand, some of these chemicals of agriculture, while 

 widely distributed, are found in only small amounts in soils. They 

 are, however, of highei^t importance in agriculture, because no plant 

 of any kind can grow in their absence, and the limited amount of these 

 correspondingly limits all the other conditions of growth. Such are 

 potash and phosphoric acid. 



Let us see how much of these materials is contained in the alluvial 

 soils of Michigan. In 38 soils, gathered from all parts of the Lower 

 Peninsula and analyzed in the chemical laboratory, the average per 

 cent of potash was found to be 1.11, and of phosphoric acid .28 per cent. 

 An acre of soil, taken to the depth of one foot, containing Lll per cent 

 of potash, would hold 40, 400 pounds of potash and 11,700 pounds of 

 phosphoric acid. The amount of these materials in bank, while rela- 

 tively small, is absolutely large. Let us see how cropping may draw^ 

 upon these deposits. Clover hay makes a heavy demand for potash, 

 two tons containing 40 pounds, yet more than eleven hundred crops 

 of such hay may be removed before the fund is exhausted, even if no 

 I>art of the crop is returned to the soil. 



The soil supjtly of potash is derived from the decomposition of rocks 

 containing the silicate of i)otash, etc.^ e. g., feldspar, a silicate of potash 

 and alumina containing 12 i)er cent of potash. Sui)])Ose we have a soil 

 made up of half sand and half feldspar — a loam. These original soil 

 materials would contain 250,920 pounds of potash. In the process of 

 decomposition much of this potash w^ould be set free in soluble condi- 

 tion and be washed away in drainage water. If four-fifths were thus 

 removed, we would have 50,184 pounds left in the clay soil remaining. 

 But the feldspar is very seldom completely decomposed, particles of 

 feldspar remaining in the clay, the successive decomposition of which 

 furnishes a supply of potash for untold ages. This is one reason for 

 the strong and persistent quality of clay soils, especially the boulder 

 clays of our western shore and some central countries. 



Conceding the great agricultural value of potash as a manure, a 

 practical question arises. How shall the farmer secure a sufficient 

 supply? He may buy it in the market, as the German .Kali Works 

 otter the Stassfurt Salts, rich in potash, for sale; or he may raise potash 

 by promoting decomposition of potash-bearing minerals in his soil, 

 especially if his land has a fair amount of clay. 



Soil materials may be placed in three general classes: Active, which 

 are chemicals in condition for immediate use, soluble in water or easily 

 dissolved by the acid juices of roofs of plants; the amount of active 

 material seldom exceeds one per cent: Reserve, not soluble or imme- 

 diately available for plant use, and for the time simply discharging a 

 mechanical office for the plant, but capable of becoming active by 

 further decomposition, and thus gradually brought into the active class; 

 not in active service now, but liable, like all reserve troops, to be 

 drafted for active service. The first, or active class, we may call cash 

 in hand; the reserve, as funds in the hands of a receiver, and liable to 

 remain somewhat indefinitely in the hands of the receiver unless we 

 demand an accounting. The third class includes the permanently insolu- 



