VERMONT AGRICULTURAL REPORT. 55 



The insoluble phosphoric acid is insoluble in water, and is but slowly 

 taken up by the plant roots, being firmly bound or held by the large 

 amount of lime. The rate of its assimilation depends largely on the 

 nature of the phosphate. That from bone is more readily used than 

 that from rock, since the decay of the organic matter honeycombs it 

 and puts it in a favorable condition for solution. That from rock, on 

 the other hand, even though ground to an impalpable powder, resists 

 solution almost indefinitely, except on very peaty soils or those con- 

 taining much humus. Relatively large proportions of available and 

 small proportions of insoluble phosphoric acid are desirable in fertiliz- 

 ers. 



FUNCTIONS OF PHOSPHORIC ACID. 



The phosphates, like the nitrates, are distributed throughout all soils, 

 but available forms, in quantities sufficient to promote a large crop 

 growth, are often lacking. This is particularly true in grain growing 

 regions since grain is a heavy user of this ingredient. 



Phosphoric acid promotes maturity and seed formation. Seeds and 

 fruit contain more phosphorus than does any other part of the plant. 

 They do not develop normally and the plant fails to mature unless a 

 fair supply of this element is available. Phosphorus acts in a manner 

 opposite to nitrogen in this respect. Phosphoric acid liberally applied 

 early in the season, unless its effect be counteracted by plentiful sup- 

 plies of nitrogen, hastens maturity. Plump, full seed indicates plenty of 

 available phosphoric acid, while a shrunken seed or its failure to set may 

 be due to its paucity. One may judge somewhat in this manner as to 

 crop needs. 



POTASH. 



Potash is a combination or union of a silver-white metal, potassium, 

 with the gas oxygen. It is a constituent of many minerals and rocks, 

 which, on decomposing, crumble into small particles and furnish potash 

 compounds to the soil. Thus it happens that potash is a common soil 

 ingredient; but it is one which is tightly locked up in combination with 

 silicic acid (the main ingredient of sand) and hence is but slowly avail- 

 able to the plants. Most plants, moreover, draw heavily upon the 

 potash supplies of the soil. Hence it is not uncommon for plant life to 

 show the effects of an insufficient supply of this constituent. The ashes 

 of plants are rich in potash. It is this material, united mostly with 

 carbonic acid, which is leached by water from wood ashes forming the 

 well known "lye." 



Potash exists in various combinations and forms. 



1. In minerals, rocks and soils. 



2. In vegetable material as organic potash. 



3. In ashes of vegetable matter, as impure carbonate, silicate, etc. 



4. In special potash minerals or salts, as muriate (chlorid), sulphate, 

 etc. 



