14 PLANT PRODUCTS 



chief chemical laws of mass action, so that the soil water 

 will always take away some ammonia from the soil. 



After the ammonia has become fixed hi the soil it still has 

 to undergo further changes. These changes are, however, 

 not purely chemical ones, but are dependent upon bacterial 

 action, and are not so easily demonstrated on the lecture 

 table or in the laboratory. They require an elaborate experi- 

 ment on the field itself. Such elaborate field experiments 

 have been carried out at Rothamsted. 



To return to our experiment with two tubes, another 

 point that can be easily investigated by such an experiment 

 is to examine the fate of the sulphuric acid part of the sulphate 

 of ammonia. 



By the use of barium chloride we can see at once that plain 

 water removes a noticeable amount of sulphuric acid from 

 the soil, and that the drainage from the manured soil 

 practically amounts to the sum of the other two quantities, 

 namely, that which sulphate of ammonia contains and that 

 which water washes out of the unmanured soil. Another 

 very important result that can be seen from this experiment 

 is the effect of the sulphate of ammonia on the amount of 

 lime in the soil. The sulphuric acid part of the sulphate 

 of ammonia combines with the lime in the soil and the two 

 go out together as calcium sulphate. A test with ammonium 

 oxalate on the drainage from the two tubes will show at 

 once that the lime lost to the soil by drainage is very much 

 greater when sulphate of ammonia is applied than when the 

 soil is unmanured. In common agricultural language, 

 sulphate of ammonia exhausts the soil of its lime. The 

 demonstration of this point on a large scale in the field has 

 been very admirably shown in the researches of the Royal 

 Agricultural Society in their experimental farm at Woburn. 

 In certain plots of barley continuous application of sulphate 

 of ammonia results in turning a light but good soil into a mere 

 desert, which grows nothing at all, except an occasional 

 weed. When, however, soil, which has been rendered 

 infertile by deliberate over-manuring is subsequently treated 

 to a dressing of lime, the fertility is recovered, and crops 



