180 The Principles of Fruit-growing. 



The actual fertility of the soil depends, therefore, upon 

 the plant as well as upon the land. The better and more 

 comfortable the plant, the more food it can appropriate from 

 a given soil ; hence that soil is practically the richer. The 

 chemist does not determine the physical conditions which 

 make the plant comfortable and active. In other words, the 

 amount of plant-food in the soil is only one of the ele- 

 ments in the fertility of the land. 



In most instances as much depends upon the physical 

 condition of the soil as upon its chemical constitution, and 

 in many cases even more depends upon it. 



Soil is derived from two sources rock and organic mat- 

 ter. Each is essential to it. Without the rock matter it 

 would lose body and staying qualities. Without the organic 

 matter it would lose life, or "heart" and activity. 



Nature adds the organic matter to the soil by growing 

 plants upon it and then incorporating their remains with it. 

 Everywhere the process of soil -building is now going on. 

 The longer the soil is in crops the richer it becomes, al- 

 though the relative amount of mineral matter which it con- 

 tains may be decreasing at the same time. 



Nature makes the soil richer, then, both by fining and 

 digesting the mineral matter and by ameliorating its physical 

 condition through the incorporation of humus or organic 

 matter. 



This fining process must ultimately cease, but the addi- 

 tion of humus never ceases. The final and complete en- 

 richment of the soil, therefore, must come largely as the 

 result of the incorporation of humus with it. 



The chief value of this humus is not to directly afford 

 plant-food, but to improve the conditions of temperature, 

 moisture, aeration and the like. 



b. Man's treatment of the land. Man's chief desire is to 

 use the organic products of the land. He consumes the 

 plant product. As a consequence, cultivated soils soon tend 

 to become hard, dense, heavy and lifeless, and the more 

 clay- like the land the more pronounced is the result. 



