WHEAT 27 



On Plot 3 wheat has been grown without manure every year since 

 1843, for four years previously no manure had been applied to the field, 

 so that the present crop is the sixty-seventh without manure After a drop 

 in production during the first few years, the yield has been practically 

 constant for the last forty years, fluctuating only with the season, and 

 showing no immediate prospect of declining. The average crop over this 

 period has amounted to about 12 J bushels per acre, approximately equal to 

 the average yield, taking the whole world over. 



Effect of Nitrogenous Manures 



Plots 6, 7, and 8 should be compared with Plot 5, since all receive the 

 same mineral manures, but different amounts of nitrogen as ammonium- 

 salts. 



Plot 5, which receives the minerals but no nitrogen, grows very little 

 more than the continuously unmanured plot ; its average over the whole 

 period is only 149 bushels, as against 131 without manure of any descrip- 

 tion. The yield of the other three plots increases with each addition of 

 nitrogen ; the grain increases from 24 bushels with 43 lb. of nitrogen, 

 to 33 bushels with 86 lb. of nitrogen, and to 37 bushels with 129 lb. of 

 nitrogen ; the straw is even more affected by a free supply of nitrogen, 

 rising from 21^ cwt. to 33 and 41 cwt. as the nitrogen is doubled and 

 trebled. 



Comparative Effect of Nitrate of Soda and Ammonium -salts 



Plot 6 should be compared with Plot 9, and Plot 7 with Plot 16. 

 Plots 9 and 16 receive nitrate of soda and mineral manures, so that Plot 9 

 has the same manuring as Plot 6, and Plot 16 as Plot 7, except that the 

 ammonium-salts on Plots 6 and 7 are replaced by equivalent amounts of 

 nitrate of soda. The manuring of Plots 9 and 16 has, however, been 

 changed during the progress of the experiments, so that they are only 

 comparable with 6 and 7 since 1885. Taking the averages of the last ten 

 years, as set out in the diagram Fig. 9, it will be seen that nitrate of soda 

 is a more effective source of nitrogen than the ammonium -salts ; the single 

 application yields 16 per cent, more grain and 26 per cent, more straw than 

 the corresponding amount of ammonium-salts ; the double application, 

 however, yields practically the same amount of grain, and only about 1 cwt. 

 more straw. 



Effect of the Mineral Constituents 



The series of Plots 7, 10, 11, 12, 13, and 14 all receive the same 

 amount of nitrogen — 86 lb., in the form of 400 lb. of ammonium-salts per 

 acre — but differ in regard to their mineral manuring. Plot 10 receives 

 nothing beyond the 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. 



Retention of Manures by the Soil 



As a rule 100 lb. of the ammonium-salts are applied in the autumn 

 when the seed is sown, the rest being reserved for a top-dressing in the 

 spring. On one of the plots, however, Plot 15, the whole 400 lb. of 



