28 N. H. AGE. EXPERIMENT STATION. [Bulletin 170 



that the amount of water-soluble potash in these soils is not a 

 limiting factor in production. These observations show that, 

 after a certain concentration is reached in the soil solution, no 

 advantage can be expected from a further concentration. Where 

 the amount of water-soluble inorganic material is increased by 

 means of nitrate of soda on the grass plots, an increase in yield 

 is always effected. This increased yield is due to the fact that 

 nitrogen has been supplied and that nitrogen is the first limiting 

 factor in the growth of the plant. Field observations show that 

 the grass plant is able to secure large quantities of potash from 

 the soil and that the supply of potassium is not an early limiting 

 factor in the production of hay. Peat soils, w^hich are relatively 

 high in organic matter, respond readily to applications of potas- 

 sium fertilizers. 



The data obtained on the effect of potassium fertilizers on the 

 yield are tabulated in Table XXI. This table shows that 

 potassium fertilizers used alone have not produced an ap- 

 preciable increased yield on these soils. The difference between 

 the potash plots and the check plots beside them are, on the 

 average of the fifty-one plots, only thirty-six pounds per acre. 



The data obtained in connection with nitrate of soda used 

 alone and with potash are tabulated in Table XXII. From 

 the data it is at once evident that when the yield is increased 

 by the use of nitrogen the natural supply of potassium is still 

 adequate. Further it does not appear that any satisfactory 

 increased yield can be obtained in a practical way by supplying 

 potash fertilizers in addition to nitrate of soda. 



The average of the ninety-three observations given in Tables 

 XXI and XXII in connection with the use of potash alone and 

 with nitrogen shows very little increase in yield. The increase 

 observed is too slight to be of any practical importance. In a 

 few cases an increased yield has been produced. These increases, 

 however, are slight and practically afford but little opportunity 

 for profit. 



The addition of phosphoric acid to potassium and nitrogen 

 fertilizers may increase the yield. In most of these observations, 

 the phosphoric acid accounts for this increase. The phosphoric 

 acid problem and its relation to the, production of hay will be 

 dealt with in a subsequent paper. 



