398 EFFECTS OF SINKING, AND REMEDIES FOR IT. 



rains .1 an equal degree with lime itself. This difficulty induced Lord 

 Dundcnald to suspect the agency of some chemical principle in produ- 

 cing the above effect.* As the lime, however, is unchanged after it has 

 descended, is still in a powdery state, and exhibits no appearance of 

 having been dissolved; it is difficult to imagine any chemical action by 

 which such a sinking could have been brought about. 



It is possible that in grass lands the earth-worms, which contribute so 

 much to the gradual production of a fine, mould, may, b) bringing up 

 the other earthy matters only, contribute to the apparent sinking of the 

 lime, as well as of certain other top-dressings.f 



The effects of this sinking are to remove the lime from the surface 

 soil, and to form a layer of calcareous matter which in wet or imper- 

 vious bottoms will harden and form a more or less solid bed or pan, 

 through which the rains and roots refuse to penetrate, and which the 

 subsoil plough in some districts can tear up with difficulty. On our 

 stiffer soils it encourages the growth of the troublesome coltsfoot, and in 

 the open ditches of the wholesome water-cress. 



The practical remedies for this sinking are of two kinds : 



1°. The ploughing of a deeper furrow, and hence one of the benefits 

 which in many localities follow the use of the trench plough (p. 322). 



2°. The sowing of deep-rooted and lime-loving crops, such as lucerne 

 and sainfoin, which in such soils not only thrive, but bring up in their 

 stems, and restore to the surface, a portion of the lime which had pre- 

 viously descended, and thus make it available to the after-crops. 



§ 20. Why liming must be repeated. 



Lime which sinks, as above described, does not wholly escape from 

 the soil, but may by judicious management be again brought to the 

 surface. Such a sinking^ therefore, does not necessarily call for the ad- 

 dition of a fresh dose of lime^ nor does it explain the reason why in prac- 

 tice the application of lime to the land must at certain intervals be every 

 where repeated. 



We have already seen that the influence of the lime we have laid 

 upon our fields after a time gradually diminishes — the grass becomes 

 sensibly less rich year by year, the crops of corn less abundant, the kind 

 of grain it will ripen less valuable. Does the lime, you might ask, ac- 

 tually disappear from the soil, or does it merely cease to act ? This 

 question has been most distinctly answered by an experiment of Lam- 

 padius. He mingled lime with the soil of a piece of ground till it was 

 in the proportion of 149 per cent, of the whole, and he determined sub- 

 sequently, by analysis, the quantity of lime it contained in each of the 

 three succeeding years. 



The first year it contained . 1-19 per cent, carbonate of lime. 

 The second year .... 0-89 « " 



The third year 0-52 " « 



The fourth year 0-24 " " | 



* «'In clayey and loamy soils, which are (7) equally ditfusible with lime, and nearly of the 

 same specific gravity, the tendency which lime has to sink cannot be accounted for simply 

 on mechanical principles " — Lord Diindonald's Agricultural Chemistry, p. 46. 



t See in a subsequent lecture the remarks on laying down to grcm ; also the Author'a 

 Elements of Agricultural Chemistry, p. 212, 



} Schiibler, Agr'.eu tural Chemie, ii., p. 141. 



