48 



EXPERIMENTS UPON WHEAT 



nitrogen, Plot 11 has superphosphate also, while 12, 13, 

 and 14 receive a further addition of sulphate of soda, 

 sulphate of potash, or sulphate of magnesia respectively, all 

 three of which are combined to form a complete mineral 

 manure on Plot 7. It should be remembered that soda, 

 magnesia, and potash are always found in the ash of plants, 

 and at the time the experiments were started little was known 

 about the part they played in the nutrition of the plant. And 



Bushels 

 perAcr. 



20 



10 



Plot 13. 

 Plot 7. 

 Plot 12. 

 Plot 14 



Plot II. 

 Plot 10. 



FIG. 6 Production of Wheat with varying Mineral Manures. All Plots receive equally 

 86 Ib. N. as Ammonium-salts. Averages over 10-year periods (1852-1911). 



although we know to-day that for practical purposes potash 

 alone of the three need be supplied in a manure, we are still 

 uncertain what is the function of the other two, which being 

 present in every plant can hardly be without some action. 

 Fig. 6 shows the crops upon these plots in successive ten- 

 yearly periods. It will be seen that Plot 11, receiving super- 

 phospl ate, has always given a better crop than Plot 10, without 

 it. This superiority was more marked in the early years of 

 the experiment, when the reserves of potash, etc., were 



