i 5 o SCIENCE PROGRESS 



a complete dressing of artificial manure including 43 lb. of 

 nitrogen per acre. 



It is difficult to account for these extraordinary results. 

 Whitney argues from his hypotheses that rotation takes the 

 place of fertilisers, and these figures at first sight lend some 

 colour to his view. But the statistics for the turnip crop put a 

 wholly different complexion on the matter. On the Agdell 

 unmanured plot turnips give a miserably poor crop of less than 

 a ton to the acre, against twelve tons or more on the manured 

 plot ; here then there is no evidence of rotation acting like a 

 fertiliser. It is difficult to believe that the small excretion 

 given off by so insignificant a crop as one ton of turnips per 

 acre could after four years be sufficiently potent to keep the 

 next crop down to the same low level. While therefore we 

 cannot accept Whitney's hypothesis we are not yet prepared 

 with another; the whole matter remains among the many 

 interesting problems as yet unsolved presented by Agdell field. 



Conclusion 



The outstanding differences between Whitney's hypotheses 

 and those more generally accepted may therefore be reduced to 

 three : 



(1) Whitney supposes all soils to be chemically alike in that 

 all are made up of the same rock material ; consequently the 

 soil solution is the same in all cases. Other chemists, on the 

 other hand, consider that the soil is more complex, containing 

 colloidal decomposition products and a solution which not only 

 differs in composition in different soils but also shows local 

 variations in composition in different parts of the same soil. 



(2) He further supposes that variations in concentration of 

 the soil solution have no effect on the rate of growth of plants 

 and that in consequence all soils are equally rich in plant food ; 

 added fertilisers owe their value to other than nutritive effects. 



(3) He considers that infertility must therefore be due to 

 other causes than lack of nutritive compounds ; dismissing 

 considerations of nutrition altogether, he supposes instead that 

 infertility arises from the presence of toxic organic compounds, 

 some of which at any rate may be plant excretions. We, on the 

 other hand, attach great importance to the nutritive functions 

 of the soil constituents and of added fertilisers; while some 



