382 THE POPULAR SCIENCE MONTHLY 



continue until the acid conditions and the depth of the accumulating 

 layer of peat would kill the trees, the stumps of which would remain 

 sealed up below the peat. I am far from thinking that this explanation 

 is complete, but at least we have facts in sight which could lead one to 

 suppose that a non-calcareous soil originally neutral and carrying a 

 normal vegetation can naturally become acid, alter the character of its 

 vegetation and clothe itself with a layer of peat. The point of economic 

 importance is that these peaty acid soils are of very little value as long 

 as they are acid, though they take on a quite different aspect if they are 

 limed and made neutral. 



Of all the soil factors making for fertility I should put lime the 

 first; upon its presence depend both the processes which produce avail- 

 able plant food in quantities adequate for crop-production at a high level 

 and those which naturally regenerate and maintain the resources of the 

 soil; it is, moreover, the factor which is most easily under the control 

 of the agriculturist. 



I need say little about those cases in which infertility is due to the 

 presence in the soil of some substance which is actually injurious to 

 plant-growth, because such substances are nearly always due to the 

 physical environment of the soil, to too much or too little water. In 

 water-logged situations we may find in the soil peaty acids, iron salts, 

 sulphides, etc., inhibiting the growth of plants ; in arid regions the soil 

 may still be charged with an excess of soluble compounds of the alkalis 

 and alkaline earths, resulting from the decomposition of the rocks that 

 have been broken down to form the soil, but which through the inade- 

 quate rainfall have never been washed out. The establishment of normal 

 conditions of growth, irrigation in the one case, drainage in the other, 

 will speedily result in the removal of the deleterious substances. Prac- 

 tically, only bodies that are soluble can get into a plant to injure it, 

 hence such bodies can be removed from the soil by water, provided that 

 the water can find its way through the soil and escape. 



Let us now consider the various methods by which land suffering 

 from one or other of the disabilities we have just discussed is nowadays 

 being brought into cultivation. The most important, if we consider the 

 area affected, is the extension of cropping into regions of deficient rain- 

 fall by means of what has been termed dry-farming. As far as its im- 

 mediate methods go, dry-farming consists in nothing more than the 

 application of the principles of husbandry worked out by English 

 farmers in the east and southeast of England, principles first expounded 

 by Jethro Tull, though a complete explanation was not then possible, 

 even if it is now. In the first place, the tilth must be made both deep 

 and fine, thus whatever rain falls will be absorbed and the conditions 

 favoring a deep and full root range will have been established. Next, 

 the soil below the surface, though finely worked, must be compact, be- 



