Continuous Growth of Wheat with Mineral Manures Alone. 39 



ammonia-salts as well as mineral manures, and the average 

 yield during those eight seasons was 29 bushels per acre, 

 or nearly 12 bushels annually in excess of the produce 

 on the unmanured plot ; whilst during the first eight 

 years of the mixed minerals, without the ammonia-salts 

 (1852-1859), the average produce was 19 bushels per acre, 

 or about 3 bushels more than the permanently unmanured 

 produce. Comparisons respecting subsequent periods are 

 afforded by the table, and it will be seen that, whilst the 



TABLE V. SHOWING THE AVERAGE PRODUCE OF DRESSED GRAIN, AND 

 TOTAL PRODUCE (GRAIN AND STRAW) PER ACRE ON PLOT 3 (PER- 

 MANENTLY UNMANURED), AND PLOT 5 (RECEIVING MIXED MINERALS 



FOB A PERIOD OF THIRTY-TWO YEARS), OVER FOUR PERIODS OF EIGHT 

 YEARS EACH, AND OVER THE TOTAL PERIOD. 



average produce of the unmanured plot for forty years was 

 14 bushels, the average of thirty-two years for the plot 

 receiving mixed minerals was 15J ; hence the application 

 of a very liberal supply of minerals has only been competent 

 to increase the yield by 1 bushels per acre per annum ! 

 Again, the average total produce for the thirty-two years 

 shows a difference of only 3 3 lib. in favour of the minerals. 

 The amount of nitrogen in this 3311b. would not exceed 31b., 

 and this represents the whole of the nitrogen which the 



