516 INVESTIGATION BY CULTURE EXPERIMENTS 



trials by the Ohio Station, such an addition produces a smaller 

 increase than any other. 



Again, suppose the farmer is adding nitrogen to his soil, as 

 most farmers are doing by growing legumes, if not in commercial 

 form. There is no more sensible or appropriate question than, 

 Will it pay to add phosphorus also? The Ohio Station reports 

 that such an addition of phosphorus will increase the yield of 

 wheat 9.72 bushels per acre annually, which is almost seven times 

 the increase produced by nitrogen alone ; but according to the 

 tests by the Bureau of Soils the increase of phosphorus added in 

 this way would be less than one fourth of that produced by the 

 nitrogen. 



So far as nitrogen and phosphorus are concerned, the perfect 

 disagreement between the water-culture method and the actual 

 field results is indeed remarkable. 



The addition of potassium produces some increases in the field 

 experiments, but they are not in accordance with the results 

 obtained with the soil-extract cultures, the lowest positive increase 

 by potassium in the water cultures being produced where its effect 

 should have been greatest, as, indeed, was the case in the field 

 trials; namely, when applied in addition to both phosphorus and 

 nitrogen. 



