BuBEAXT OF Agkiotjlttjbb. 163 



No one can doubt that phosplioms is the first limiting 

 element in this soil. Limestone has rendered the phos- 

 phate more effective on the com crops which were grown 

 before legumes in the rotation. On a soil like the one 

 at London I would unhesitatingly recommend the use of 

 phosphate and limestone for the permanent improvement 

 of the soil. It may prove to be desirable to use potash 

 along with the phosphate when limestone cannot be used, 

 as these results seem to indicate, although it must be 

 stated that the acid phosphate-potash plots are on the 

 naturally best soil of the field. However, I do not hesi- 

 tate to say, as I have frequently said, that carefully con- 

 ducted experiments may show the need of the regular 

 use of potash on this soU, although I am yet in doubt 

 in the matter. These experiments have not yet gone far 

 enough to restore organic matter to the soil, as practi- 

 cally no manure has yet been returned. If potash is 

 shown to be necessary on these soils, then I shall rec- 

 ommend its use as strongly as at present I recommend 

 phosphates and limestone, but only in connection with 

 a liberal use of phosphates. 



On the Lexington soil experiment field which has 

 been in operation four years and from which we have 

 obtained 4 com crops, 3 soy bean crops and 2 wheat 

 crops, the average total production per acre of these 9 

 crops for all plots where potash has been used either 

 alone or in combination with limestone and acid phos- 

 phate, is 281 bushels, and for similarly treated plots ex- 

 cept for potash, the yield is 283 bushels. These aver- 

 ages are made up from 72 yields extending over a period 

 of four years. One clover crop from this field shows an 

 average yield of clover hay of 3,845 pounds per acre 

 on all plots receiving potash either alone or in combina- 

 tion with limestone and acid phosphate, while plots sim- 

 ilarly treated except for potash show an average yield 

 of 3,817 pounds. No commercial nitrogen was used in 

 these tests, but that nitrogen was not a limiting element 

 before potassium is shown by the fact that potash gave 

 no increase in clover and soy beans, which are not lim- 

 ited in their growth by the lack of nitrogen in the soil. 



In passing, we may say that phosphorus and lime- 

 stone were also without results on these crops on this 

 soil. 



