EXHAUSTION OF LIME 25 



in such a form that the sulphuric and nitrous acid can 

 combine with them ; but in the majority of cases carbonate 

 of lime is the basic material present in greatest quantity in 

 the soil, and the one which is chiefly used in these reactions, 

 and it w r ill be convenient for our present purpose to speak of 

 the base required as carbonate of lime. 



A simple chemical calculation shows that i cwt. of com- 

 mercial sulphate of ammonia will require about 82^ Ibs. of 

 dry carbonate of lime for combination with the sulphuric acid 

 present. A portion of this sulphuric acid may be taken up as 

 plant food, but the quantity of sulphuric acid required by 

 crops is small, so that the greater part of the sulphate of lime 

 produced will remain unused in the soil, and, in the majority 

 of cases, will be finally removed in the drainage water. 



In the process of nitrification the i cwt. of sulphate of 

 ammonia will require a second quantity of 82^ Ibs. of car- 

 bonate of lime, or its equivalent in other bases, in order to 

 form successively the nitrite and nitrate which are the result 

 of this operation. Of the nitrate of lime so produced the 

 greater part may be taken up by the crop, while some will 

 appear in the drainage water. What the plant does with the 

 nitrate which it takes up has not yet been sufficiently studied. 

 The plant undoubtedly retains far more of the nitrogen than 

 of the base with which this nitrogen was combined in the soil, 

 and we must therefore assume that a large part of the basic 

 constituent of nitrates is returned somehow to the soil. \Ye 

 must, therefore, apparently not reckon the whole of the second 

 82^ Ibs. of carbonate of lime as lost to the soil, and perhaps 

 only a small part of it should be so reckoned in the case of 

 cereal crops. 



The exhaustion of the carbonate of lime will clearly 

 remain the same, even if no drainage water leaves the soil. 

 In this case the carbonate of lime will disappear, while sul- 

 phate of lime takes its place. The sulphate cannot, however, 

 take the place of the carbonate in the fixation and nitrification 

 of sulphate of ammonia : the exhaustion is thus nearly as 

 serious whether drainage occurs or not. 



Lime was determined by Dr. Voelcker and Dr. Frankland 



