OHIO FIELD EXPERIMENTS 451 



elements, being sufficient to pay for the phosphorus (even in acid- 

 phosphate) and leave a net profit of 200 to 300 per cent. The use 

 of commercial nitrogen or potassium, alone or in combination, is 

 of doubtful advantage with potatoes at 30 cents, but at 50 cents 

 for potatoes the potassium has been a good investment, although, 

 with sufficient manure or clover plowed under to supply the nitro- 

 gen, it is very probable that abundance of potassium would have 

 been liberated from the soil. 



Potatoes draw heavily upon potassium, and ultimately, on level 

 land which neither receives deposits from overflow nor loses par- 

 tially exhausted soil by erosion, potassium must become so defi- 

 cient as to limit the crop yield, even with the best efforts to main- 

 tain adequate supplies of active organic matter; but the total 

 supply of potassium in 2 million pounds of this Ohio soil is suffi- 

 cient for 200 bushels of potatoes every year for more than 500 

 years, and the land has sufficient surface drainage to insure some 

 soil erosion. 



Another series of long-continued and very valuable experiments 

 have been conducted by the Ohio Station on the Strongsville experi- 

 ment farm, on a quite different type of soil, of nearly level topog- 

 raphy, higher clay content, and less perfect physical condition. 

 The surface acre-foot of Wooster soil contains, as a general average, 

 about 2770 pounds of nitrogen, 1700 pounds of acid-soluble phos- 

 phorus, and 7310 pounds of acid-soluble potassium, while the 

 corresponding figures for the Strongsville soil are 6520, 1700, and 

 6300. Thus the Strongsville soil averages more than twice as rich 

 in nitrogen, but somewhat poorer in acid-soluble potassium, while 

 the phosphorus content is practically equal in the two soils. 



Table 84 gives the average results obtained from a series of 5- 

 year rotation experiments (1896-1897-1898 to 1907). The plant- 

 food materials are 440 pounds of sodium nitrate (and 50 pounds 

 of dried blood), 320 pounds of acid phosphate, and 260 pounds 

 of potassium chlorid. (One plot (No. 12) receives 680 pounds 

 of sodium nitrate.) 



The more marked effect of phosphorus on the Strongsville soil 

 is doubtless due to the larger supply of organic matter, the decom- 

 position of which tends to furnish nitrogen and liberate potassium. 

 As an average, the crops from the best-yielding plots have removed 



