46 N, H. AGR. EXPERIMENT STATION. [Bulletin 142 



It is therefore reasonable to conclude from four successive 

 seasons of work that on clay and clay loam soils the hay crop 

 can obtain all the potash it needs from the potash compounds in 

 the soil itself, and that there is sufficient potash available to 

 supply the demands of the crop without any evidence of ex- 

 haustion. 



THE WATER SOLUBLE POTASSIUM IN THE SOIL. 



By another method of studying the availability of the soil- 

 potash similar conclusions were reached regarding the continuous 

 solubility of the potash compounds naturally present in the soil. 

 The amount of potassium (the element from which potash is 

 formed) which was soluble in water was determined in nearly 

 all of the soils that have been discussed in the previous pages. 

 The analyses were all made by the methods given in Bulletin 

 31, Bureau of Soils, United States Department of Agriculture, 

 and the amounts were expressed as parts per million of the 

 dry soil. 



These determinations were all made soon after the hay crop 

 was harvested, and therefore after the plants had used all the 

 potash required for the season's growth. 



The results for 1905 are arranged in two groups, upland and 

 lowland, as in the case of total potash, and while both series of 

 soils have equally low minimum results the lowland soils have 

 a higher maximum and average than the upland soils, and the 

 proportion of average total potash to soluble potassium is prac- 

 tically the same for the two groups. This is in accord with the 

 facts that clay is richer in total potash than the other soil con- 

 stituents and at the same time is formed of the smallest soil 

 particles, which dissolve more readily than the coarser particles 

 of silt and sand. 



In 1907, 1908 and 1909 the potassium soluble in water was 

 determined in the soils of eight of the plats in the fertilizer 

 series, four of which were unfertilized, while the other four had 

 been dressed with potash salts. The application of soluble pot- 

 ash had been thoroughly fixed in the soil, so that in spite of vari- 

 ations in crop yield, potash removed by the crop and potash ap- 

 plied as top-dressing, the amounts of potassium found to be 

 soluble in water were practically the same for all plats in all the 



