HORTICULTURAL SOILS. 



G9 



that fall victims to organic law. We have to remember, further, 

 that the greater part of the weight of every plant is obtained 

 from the air, and only a very little is derived from the soil. 

 Not only so, but it is a fact, and a very important one, that new 

 plants grow much more quickly than the remains of the old 

 ones decay and disappear ; hence organic carbonaceous matter 

 must always be increasing in a soil left in a state of nature and 

 uncultivated. 



The character and amount of plant-growth is found to differ 

 considerably in different soils, and the largest quantity of 

 produce will be grown on the soils where the wild plants could 

 get the greatest amount of food. It happens, therefore, that the 

 virgin soils, as they are termed, derived from the heath, the 

 forest, or the prairie, which are first ploughed up by the settlers 

 in new countries, are richly charged with a blackish -brown 

 vegetable substance, known under the general name of humus, 

 and recognised as one of the marks of a fertile soil. In fact, 

 humus was considered by agricultural chemists in the early part 

 of the present century to be the main source of soil fertility. 



But without supposing that plants feed directly upon humic 

 matter, it is easy to see why the proportion of this substance is 

 often a very fair measure of the productiveness of a soil, for the 

 reason that it represents the material accumulated by a previous 

 succession of crops. 



Table III. shows the proportion of organic matter, and of 

 nitrogen in the organic matter, in seven descriptions of soil, in 

 quantities per acre, the soil being cut to 9 inches deep. 



TABLE III. — Organic Matter and Nitrogen in Different Descriptions 

 of Soil per acre, cut to 9 inches deep. 



Description of soil 



Organic matter 



Nitrogen 





lbs. 



lbs. 



Arable loamy soil . 



34,500 



3,360 



Pasture soil .... 



76,050 



5,558 



Prairie soil .... 



117,225 



9,630 



Forest mould .... 



126,900 



6,750 



Leaf mould .... 



141,950 



8,805 



Peat mould .... 



188,000 



5,000 



Heath mould (Ghent) 



640,000 



11,650 



The figures show a very considerable range in the amount of 



