EXHAUSTION OF LIME 27 



only in those cases in which the amount in the soil was origin- 

 ally very small. If we take the weight of dry surface soil 

 turned over by the plough as 2,000,000 Ibs. per acre, then one 

 per cent, of carbonate of lime in the soil will amount to 20,000 

 Jbs. per acre. The soil of the unmanured plot in the Roth- 

 amsted wheat field contains in the first nine inches, according 

 to Dr. Dyer's analysis, nearly 3 per cent, of carbonate of lime ; 

 but there is very little in the subsoil. Plots in this field 

 have received very large quantities of ammonia salts annually 

 during 55 years without any falling off having been experi- 

 enced in the produce from the manure where the necessary ash 

 constituents have been supplied. 



In the experiments on the old pasture land at Rothamsted 

 exhaustion of lime has been felt. The surface soil of an old 

 pasture is usually poor in lime. Such a soil is rich in vege- 

 table remains, and the carbonate of lime of the original soil 

 has been gradually dissolved and removed by the action of the 

 carbonic and humic acids arising from the decay of vegetable 

 matter. The experimental trials with ammonia salts, and 

 other manures, on a portion of the Park at Rothamsted, com- 

 menced in 1856, and for many years the ammonia salts yielded 

 a large and satisfactory increase of produce. Bare patches 

 then began to appear on some of the plots receiving ammonia 

 salts, notably on that receiving ammonia only, and that 

 receiving the largest quantity of ammonia (600 Ibs. of 

 ammonia salts per acre) with superphosphate and alkali salts. 

 This occurred notwithstanding that the dressing of ammonia 

 salts was divided into two applications, so as to avoid if 

 possible any direct injury to the herbage. No bare patches 

 appeared save where ammonia salts had been applied. In 

 1 88 1 a part of the plots was treated with a dressing of chalk, 

 and this being found to remedy the condition in question, the 

 application of lime and chalk has since been extended to all 

 the grass land under experiment. 



In the long continued experiments at Woburn the evil 

 effect resulting from the removal of lime has apparently made 

 its appearance in the barley field. The soil at Woburn is a 

 fine sand, and contains very little lime. In reporting on the 



