4:9 N. H. AGR. EXPERIMENT STATION. [Bulletin 142 



seems reasonable for grass, since both crops require about the 

 same soil conditions. 



In 1908 four plats yielded an average crop of 6,782 pounds of 

 hay per acre, and these crops removed an average of 104.4 

 pounds of potash from the soil. The actual dry matter in these 

 crops was about 6,000 pounds, therefore there had been used 

 approximately 1,800,000 pounds of water, and in this amount 

 of water had been dissolved the 104.4 pounds of potash found 

 by analysis, which is equivalent to a concentration of fifty-eight 

 parts of potash in one million parts of water. 



In one sentence, then, we may say that we have found the 

 average concentration of the potash in the soil water to be 

 eighty parts per million, and the approximate concentration 

 required for the heaviest yields of hay was fifty-eight parts per 

 million. 



Therefore on our clay loams, with a total content of potash 

 ranging from forty to sixty tons per acre in the first foot of 

 the soil, field experiments and laboratory analyses show that the 

 grasses have obtained and can continue to secure from the soil 

 all the potash they need for large crops. In this discussion no 

 mention is made of the fact that diffusion of potash occurs from 

 the soil moisture into the plant when the concentration drops 

 within the plant walls. This phenomenon increases the ade- 

 quacy of the soil potash. 



Our clay loam soil, when kept in proper condition with humus, 

 as shown in our Bulletin 138, and supplied with nitrogen and 

 phosphoric acid, will supply the potash without reinforcement. 



HOW TO INCREASE THE AVAILABILITY OF THE 



SOIL POTASH. 



The method which suggests itself from the results obtained 

 by the field experiments is the frequent use of clover in a ro- 

 tation. It has been noted that applications of potash had no 

 effect in developing clover when compared with unmanured 

 plats beside the potash plats, and further, that the clover on the 

 unmanured soil contained practically the same amount of potash 

 as on the potash plats. The average percentage of potash in the 

 dry matter of clover from fifteen different plats in 1907 was 



