52 EXPERIMENTS UPON WHEAT 



plots. Thus in 1910 Plot 17 received ammonium- salts but no 

 minerals, and Plot 18 the minerals without the ammonium- 

 salts, and the treatment was reversed in 1909 and again in 

 1911. It will be seen from the diagram, Fig. 8, that the plot 

 which in any year is receiving minerals without nitrogen 

 derives little or no benefit from the ammonia it had the 

 year before. The crop shows every sign of .nitrogen starva- 

 tion, and amounts on the average to only 15 '3 bushels of 

 grain, as compared with 14*9 bushels on Plot 5 which has 

 received minerals without any nitrogen every year since 1852. 

 On the E-othamsted soil, then, we may conclude that the effect 

 of sulphate of ammonia applied to a cereal crop is confined to 

 the season of its application. In the seasons when the 

 ammonium- salts are applied the crop is but little short of that 

 on Plot 7, where minerals are used every year with the same 

 amount of ammonium-salts, thus showing that the previous 

 mineral manuring is carried forward and has an effect in 

 seasons beyond the year of its application. 



Much of our knowledge of the process of nitrification, by 

 which not only ammonium-salts but other compounds of 

 nitrogen, such as are contained in dung, are converted into 

 nitrates, was worked out in the Kothamsted Laboratory by Mr 

 Warington. From the continued analyses that have been made 

 of the water flowing from the drains beneath the Broadbalk 

 wheat plots, we learn that not only may readily nitrifying 

 manures suffer great losses through nitrates forming and being 

 washed out when a crop does not occupy the ground, but that 

 the same causes lead to continuous loss of nitrogen from all 

 cultivated land. This loss is at its highest when heavy rain 

 falls after the land has been broken up after harvest ; then the 

 conditions occur which are most favourable to nitrification, 

 i.e., warmth, moisture, aeration, and stirring of the soil. Thus 

 analyses of the soil show that, despite the fact that much larger 

 amounts of nitrogen are applied to Plots 7 to 18 than are re- 

 moved in the crop, the soil is not getting any richer in nitrogen ; 

 and even on Plots 2 and 19, where organic compounds of 



