THE ROTHAMSTED EXPERIMENTS 367 



tains any phosphorus, for example. If the 87 pounds of acid- 

 soluble phosphorus contained in 2 million pounds of the surface 

 soil of an acre of the level upland " barrens " of the Highland 

 Rim of Tennessee were all distributed in a coating of uniform 

 thickness over the surfaces of all the soil grains in the stratum, it 

 is very possible that, if all other essentials were provided in abun- 

 dance or perfection, the abundant sunshine and rainfall of Ten- 

 nessee would bring forth from that soil hundred-bushel crops of 

 corn for three successive years, or possibly longer, because, accord- 

 ing to the Tennessee Experiment Station (Bulletin 3, Volume X, 

 1897), there are 61 pounds of acid-soluble phosphorus in each 

 2 million pounds of the subsoil. 



Absolute science shows no necessary relation between the 

 amount of potassium, for example, that may be dissolved from 

 100 grams of soil by 500 grams of water, during twenty minutes 

 of laboratory manipulation, and the amount of the same element 

 that a corn plant may secure from a cubic yard of earth during 

 the fou? months' period of growth. 



Referring again to the Broadbalk field data, it will be seen 

 that even where 86 pounds of nitrogen are applied (plot 10), the 

 average yield is only 20.4 bushels, or 18.6 for the last 25 years; 

 and the increase of 6.6 bushels by nitrogen alone is raised to 21.2 

 bushels (or to 33.2 bushels per acre) when both nitrogen and 

 minerals are supplied. Under these conditions, nitrogen and phos- 

 phorus are powerless to maintain the yield (see plot n); for, 

 although the soil contains abundance of potassium and other less 

 important essential elements, there is evidently but little action 

 in the soil by which they can be made available. One is inclined, 

 for the land's sake, to wish that one or two good crops of clover 

 might be plowed under on plots 5 and u, were it not for the fact 

 that these plots are far too valuable for the lessons they are now 

 teaching to justify any such change. 



It is even questionable whether the effect of the potassium ap- 

 plied to plot 13 is wholly due to the use of that element as plant 

 food, or perhaps due in part to its power to hold other elements, 

 as phosphorus, in available form. It will be observed that during 

 the first 30 years sodium and magnesium salts (applied in molec- 

 ular proportions) produced essentially the same increase (about 



