278 



THEORIES OF FERTILISER ACTION [chap. 



would withdraw from the soil approximately the follow 

 ing fertilising materials. 



Table LXXXV.— Fertilising Constituents contained 

 IN Wheat and Barley Crops. 



Now the results of field -experiments, which are 

 abundantly confirmed by ordinary farming experience, 

 go to show that the yield of wheat is chiefly determined 

 by the supply of nitrogen ; phosphoric acid is of second- 

 ary importance, and only on exceptional soils will there 

 be any return for the application of potash. With 

 barley, though its composition is very similar to that 

 of wheat, the results are very different : nitrogen is still 

 the most important element in nutrition, but phosphoric 

 acid has equally marked effects, whilst in ordinary soils 

 potash counts for little or nothing. 



This may be illustrated from the Rothamsted experi- 

 ments, and the part played by the reserves in the soil 

 will be made evident by comparing the results obtained 

 in the first and the fifth series of ten years. 



The analysis of the barley plant would indicate that 

 it requires nitrogen in the largest amounts, then potash, 

 and, least of all, phosphoric acid ; but if the results for 

 the first ten years of the experiment are considered, it 

 will be seen that the omission of either nitrogen or 

 phosphoric acid from the fertiliser causes a big decline 

 in yield in comparison with that of the completely 

 fertilised plot. The omission of potash, however, is of 

 little or no moment, since it only causes the yield to fall 



