42 THE PRINCIPLES OF 



At one time it was thought to be all-important, and I do 

 not doubt its importance ; but there may be a very small 

 amount of plant food, and yet a fertile soil if the plant food 

 is in such a state that the plant can readily get at it. On 

 the other hand, we may have a rich soil in which the tenacity 

 of the soil or other circumstances make it very difficult for the 

 plant to get at the plant food. The plant food may be locked 

 up. Hence chemical analysis does not always give us such 

 a ready key to the fertility of a soil as we might expect. 



A great deal depends, as already pointed out, upon the 

 ease with which the roots can pursue and capture their food, 

 if I may so speak, all of which is not very easily indicated 

 in a sample of soil. In such a case we cannot tell very 

 much what the exact conditions of the soil are. We read 

 the analysis, but require to know a great deal more before we 

 can come to a conclusion as to whether it is a fertile soil at 

 all. Nevertheless, we shall put as the first condition plenty 

 of plant food in an available form. 



What other conditions of fertility are there ? A very 

 important one indeed is that the soil should be deep, because 

 i a thin soil of three or four inches only in depth, though a rich 

 one, may not be half or a quarter as good as a soil in which 

 there is a depth of a foot or a couple of feet. There must be 

 quantity, in fact, as well as quality, and you have a guarantee 

 of quantity in the depth. In addition to a high percentage 

 of plant food, I say, we must have depth of soil. This is, 

 then, a second condition of fertility. 



A third condition 'of fertility is the absence of directly 

 injurious substances from the soil, such as sulphate of iron or 

 green vitriol, and sulphide of iron or iron pyrites. These may 

 be directly injurious substances in a soil. Among these are 

 also substances of a sour character, as, for instance, partially 

 decomposed vegetable matter. It is a condition of fertility 

 that such substances should be absent. 



