May, '14] GRANITIC SOIL POTASSIUM. 5 



oxide is higher than the average application per acre. In a soil 

 which carries 2% potassium oxide, the amount per acre foot 

 totals sixty thousand pounds. In comparison with sixty thousand 

 pounds sixty becomes a very small quantity. Under such con- 

 ditions, one pound is added to one thousand pounds already 

 present. 



The soils on which the experiments reported in this work were 

 made represent fairly well the hay soils in this state. They were 

 formed from granitic rocks by the grinding action of the glaciers 

 and subsequent w^eathering processes. These soils usually lie upon 

 a foundation of ledge in the uplands and upon beds of boulder 

 clay in the lowlands. In some of the lowlands, the boulder clay 

 comes near the surface and forms the subsoil and at one time con- 

 stituted the surface soil. 



Early in the history of the Experiment Station, several analyses 

 were made of the heavy clay soils on the college farm which showed 

 1% of potassium oxide soluble in strong acid. This would be 

 equivalent to thirty thousand pounds of potassium oxide in the 

 upper foot of an acre of soil. This enormous amount of potassium 

 was believed to be unavailable to plants, or else so slowly soluble 

 as to be of little use to the growing crop. , 



Observations on the hay crops grown on these soils for several 

 successive years showed that the grass plant was able to make 

 use of the soil potassium. The problem presented by these ob- 

 servations was the determination of the rate of availability of 

 the natural potassium compounds and whether this rate was 

 sufficiently rapid^o produce a large crop without exhausting the 

 soluble compounds. 



Clay soils formed from granitic rocks are naturally rich in 

 compounds of potassium because they are principally made by 

 the pulverizing of feldspar with is one of the constituents of 

 granite, and richest in potassium of any of the common minerals. 

 Feldspar may carry from 6 to 14% potassium oxide. Sandy 

 soils, on the other hand, are largely formed from quartz, another 

 mineral in granite which is harder than feldspar, does not pulver- 

 ize as easily and contains no potassium. However, some of our 

 so-called sandy soils are mixed with large quantities of minerals 

 which carry large amounts of feldspathic material and some cla}^, 

 and, on the whole, contain considerable amounts of potassium. 

 The intervale sands are usually very poor in mineral constituents. 



