82 



EXPERIMENTS UPON BARLEY 



Comparing Plots 2 and 4, we see that a manure supplying 

 phosphoric acid and nitrogen is almost as effective as a complete 

 manure containing also potash and the other alkaline salts. 

 There is a great increase of crop caused by the superphosphate 

 and nitrogen on Plots 2, over the nitrogen alone on Plots 1, 

 and very little further increase for the further addition of 

 potash and other alkaline salts on Plots 4. Where the nitro- 

 genous manure is nitrate of soda or rape cake, the omission of 

 the potash on Plots 2 compared with Plots 4, receiving a 

 complete manure, shows no effect, whether Ave make the 

 comparison over the whole period or for successive ten-year 

 periods. With ammonium-salts, however, as the source of 

 nitrogen the omission of potash does eventually diminish the 

 crop ; for the first thirty years the crops on Plots 4 A and 2 A, 



Table XXXIII. — Batio of yield of Barley (Grain) loithout Botash to yield 

 with Botash, for successive 10-year periods, Ammonium-scdts and Nitrcde 

 of Soda being the respective sources of Nitrogen. 



with and without potash, were equal, but in the fourth decade, as 

 the soil became depleted by the continual removal of potash, 

 the crop on Plot 2 began to fall off, and the diminution is much 

 increased in the next decade. That there is no similar falling-off 

 in the yield of the corresponding plot receiving nitrate of soda, 

 is partly due to the greater root-range induced by the soluble 

 nitrate, and partly to the effect of the soda base of this salt in 

 rendering available to the plant the potash reserves of the soil. 

 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 A, receiving nitrate of soda and 

 superphosphate, the omission of potash has made no difference 

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



