QUALITY OF CEOP 83 



Table XXXIII. shows very clearly how the omission of 

 potash begins to tell upon Plot 2 A, manured with ammonium- 

 salts and superphosphate, after the first thirty years, whereas 

 on the corresponding Plot 4 AA, receiving nitrate of soda and 

 superphosphate, the omission of potash has made no difference 

 to the yield up to the end of the sixty-year period. The figures 

 show the ratio the yield of Plot 2 (without potash) bore to that 

 of Plot 4 (with potash), during each decade. 



Thus the yield on Plot 2 A (ammonium- salts and super- 

 phosphate), which for the first thirty years was practically equal 

 to that on Plot 4 A (ammonium-salts, superphosphate and 

 potash), showed a decrease of 10 per cent, in the fourth decade 

 and 23 per cent, both in the fifth and also in the sixth; whereas 

 the corresponding yield on Plot 2 AA (nitrate of soda and 

 superphosphate) is as good as that of 4 AA (nitrate of soda, 

 superphosphate and potash) up to the end of the sixth decade. 



Potash plays a less important part than phosphoric acid 

 in the manuring of barley. Very little increase of crop has 

 resulted from its use on the Kothamsted soil, and the only 

 indication of the supply in the soil giving out has been seen in 

 the last twenty years on the plot receiving superphosphate and 

 ammonium -salts. Of course the Rothamsted soil starts with 

 a very large original store of potash. 



Speaking generally, we find that barley is much more 

 dependent on a supply of mineral manures than is wheat, a 

 free supply of phosphoric acid in particular being essential to 

 its proper development. 



D. Character of the Crop as affected by Manuring. 



Table XXXIV. shows some of the characteristics of the 

 barley crop during the fourteen years 1889-1902 compared with 

 the average market valuations put upon the samples by Mr 

 Few, of Cambridge, who examined them from year to year. 

 The current market price prevailing at the time (of the 

 valuation is taken as 100, and the value put on each sample 

 is calculated on that basis. The first thing that becomes 



