34 BROADBALK FIELD 



salts; the single application yields 16 per cent, more grain and 26 per 

 cent, more straw than the corresponding amount of ammoniuni-salts ; the 

 double application, however, yields practically the same amount of 

 grain, and only about 1 cwt. more straw. 



Effect of the Mineral Ccnstituents. 



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 

 ammonium-salts is applied in the autumn, otherwise the manuring is 

 identical with that of Plot 7. The crop, however, on Plot 15 is on the 

 average below that of Plot 7, showing that some loss takes place when 

 the ammonium-salts are applied before the plant is able to utilise them. 

 Plots 17 and 18 further illustrate the fate of ammonium-salts. These 

 plots receive the dressing of Plot 7 — 400 lb. ammonium-salts and com- 

 plete minerals — but the ammonium-salts and the minerals are applied in 

 alternate years to the two plots. Thus in 1912 Plot 17 receives ammo- 

 nium-salts but no minerals, and Plot 18 the minerals without the 

 ammonium-salts, and the treatment is reversed in 1911 and again in 1913, 

 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 starvation, and amounts on the average to 

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

 has received minerals without any nitrogen every year since 1852. On 

 the Rothamsted soil, then, we may conclude that the effect of sulphate of 

 ammonia applied to a cereal crop is confined to the season of its applica- 

 tion. In the seasons when the ammonium-salts are applied the crop is but 

 little short of that on Plot 7, and sometimes (as in 191 1) is even greater 

 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. 



