286 



IMPORTANCE of DEPTH OF SOIL. 



new returns of abundant corn. Other causes, as we shall hereafter see, 

 generally operate in bringing about this kind of natural recovery, but 

 there can be no question that in circumstances such as I have now 

 adverted to, this recovery may be effected in a much shorter period 

 of time. 



4°. Importance of depth and uniformity of soil, — If the surface soil be 

 of a fertile quality, ample returns will be sure from many cijltivated 

 crops. But where the subsoil is similar in composition to that of the 

 surface — not only may the fertility of the land be considered as almost 

 inexhaustible, but those crops also which send their roots far down will 

 be able permanently to flourish in it. This fact is illustrated by the 

 composition of the following soils from the neighbourhood of Bruns- 

 wick : — 



1. 



2. 



Soil. Subsoil. Subsoil. 



Silica and fine Quartz Sand . 94-724 97-340 90-035 



Alumina 1*638 0-806 1-976 



Oxides of Iron . . . . > ^.q^^ 51-126 6-815 



Oxides of Manganese . . J ^ " J 0-075 0-240 



Lime 1-028 0-296 0-022 



Magnesia trace 0-095 0-115 



Potash and Soda 0-077 0-112 . 0-300 



Phosphoric Acid 0-024 0-015 0-098 



Sulphuric Acid 0-010 trace 1-399 



Chlorine 0-027 trace trace 



Humic Acid 0-302 0-135 — 



Insoluble Humus .... 0-210 — — 



100 100 100 



The first of these soils produced excellent crops of all deep-roofed 

 plants — lucerne, sainfoin (esparsette), hemp, carrots, poppies, &c. — and 

 with the aid of gypsum, red clover, and leguminous plants (vetches, 

 peas, and beans), in great luxuriance. The former of these facts is ex- 

 plained by the great similarity in constitution which exists between the 

 surface and the under soils. To deep-rooted plants also the magnesia, 

 in which the surface is deficient, is capable of being supplied by the under 

 soil. The effect of the gypsiim is accounted for by the almost total ab- 

 sence of sulphuric acid in the subsoil, but which the application of gyp- 

 sum has introduced into the upper soil. 



The second soil was taken from a field in which sainfoin died regu- 

 larly in the second or third year after it was planted. This was naturally 

 attributed to something in the subsoil. And by the analyses above 

 given, it was found to contain much sulphuric acid in combination with 

 oxide of iron, forming sulphate of iron (green vitriol). This salt being 

 noxious to plants, began to act upon the crop of sainfoin as soon as the 

 roots had gone so deep as to draw sufficient supplies from the subsoil, 

 and it thus gradually poisoned them, so that they died out in two or three 

 years. 



