192 



The deflocculating effect of potash salts, is pointed out in 

 Chapter VI, as demonstrated by the appearance of the soil on 

 certain of the experimental plots at Rothamsted, where considerable 

 amounts of potash salts are applied every year. 



The percentages of water in Rothamsted soils referred to in 

 Chapter VII, show that the dunged soil, rich in humus, has re- 

 tained more of the comparatively recent rainfall near the surface, 

 so that the top soil was moister, while the subsoil was drier. 



Perhaps one of the more important chapters is Chapter IX, 

 where the action of lime is rightly emphasized. 



" It is difficult to exaggerate the improvement that lime effects 

 in the dryness and workability of strong soils, which in many 

 cases would not be fit for arable cultivation had they not been 

 so treated. It has been already mentioned that on the Roth- 

 amsted estate the custom of chalking has added from 2 to 5 per 

 cent of carbonate of lime to the surface soil, which is otherwise 

 non-calcareous ; but on one of the fields, formerly under experiment, 

 the treatment has never been carried out. This field, Geescroft, for- 

 merly carried experimental crops of oats and beans ; but during the 

 rainy seasons about 1879 tne l an d lay so persistently wet late in 

 the spring that on several occasions a tilth could not be obtained 

 in time for sowing, and the land had to lie fallow, until at last 

 cultivation was abandoned and the field was allowed to fall down 

 into grass. Even now the herbage is very inferior and shows the 

 wet character of the soil by the prevalence of Air a ccespitosa; yet 

 in situation, drainage, and mechanical composition this soil is in 

 no respects different from that of the other Rothamsted fields. 

 The essential factor which has caused all the difference in the cha- 

 racter of the two soils is the absence of calcium carbonate from 

 the Geescroft field, which for some reason had escaped the chalking 

 given to the other fields. The physical improvement of a clay soil 

 by lime is not apparent at once but grows from year to year after 

 the application of lime ; the flocculating action is really not due to 

 the lime itself but to the soluble calcium bicarbonate which arises 

 from the action of water and carbonic acid upon the calcium car- 

 bonate formed from the lime. " 



In Chapter X, it is stated that, " as it stands at present, Whit- 

 ney's theory must be regarded as lacking the necessary experimental 

 foundation " ; on the other hand, the Rothamsted experiments 

 " have shown that wheat can be grown continuously upon the same 

 land for more than fifty years, and that the yield when proper fer- 

 tilisers are applied remains as large in the later as in the earlier 



