162 



it be by means of the animals' refuse or by the decay of the vegetation, 

 the material which the plants have taken out of the soil is returned 

 to it; nothing is permanently removed. 



Further, this decay causes an accumulation at the surface, of plant 

 food that has been brought up from below, where the roots have been 

 feeding. This accounts for the large return from virgin forest land. 

 That the fertility of such land very soon declines after being brought 

 under cultivation, is the expericLce of every planter. There are 

 several reasons for this. First, the working of the land causes oxida- 

 tion. The supply of oxygen, that the air carries into the soil, enter8 

 into combination with the accumulated organic matter, or humus, 

 causing some of it to become more soluble, some to be converted into 

 gases. The soluble matter will be used by plants or be lost by drain- 

 age ; the gases will escape into the atmosphere. The second result of 

 cultivation is that a better system of natural drainage is secured by 

 means of which much soluble matter will pass out of the soil in the 

 drainage water. But the source of loss which is most considerable, 

 lies in the permanent removal of produce from the land for market 

 and export purposes. Regarding the matter from the point of view 

 of the soil's fertility, we can imagine an almost ideal state of affairs — 

 that is when the whole of the produce of a property is consumed on 

 the property, and all the excrement of the consuming animals is re- 

 turned to the soil In such a case the decline in fertilitj^ would be 

 reduced to a minimum. Such a system is not expedient for the simple 

 reason that most cultivators aim at supplying produce on a larger scale. 

 It is, then, chiefly this permanent removal of produce from the land 

 that causes the fertility to decline. Common justice calls for some 

 return for this removal. The loss is greatest in the case of the cultiva- 

 tion of such plants as are grown for their whole structure, when prac- 

 tically the whole plant is removed, as, for example, cabbages, and 

 guinea-grass, when cut. 



On the other hand in the cultivation of many fruit trees the bulk 

 removed is far less. In the case of such crops as yams, the main bulk 

 of the plant need not be removed from the soil, though in too mtiny 

 cases the vines" are burnt. Such an unwarrantable waste of plant 

 food cannot be condemned too strongly. The cultivator of new land 

 should bear in mind that his land will soon fail to give him good re- 

 turns, if he does not give it a reasonable chance. He must endeavour 

 to keep up the fertililty as long as he can, and he can do so in several 

 ways. Thus, he must return to the soil as much as possible of what 

 he takes out of it. The useless, or rather unmarketable, portions of 

 the crop should be allowed to decay in the soil. Such substances, 

 though not immediately available to the plant, wdll increase the 

 amount of plant food in the soil and will gradually become more and 

 more available. They will by reason of their decay also exert indirect 

 influences for the good of the soil 



Exhaustion of the soil can be still further postpon'^d by a judicious 

 succession of crops. Nothing exhausts land so rapidly as the growing 

 of the same crop season after season, [t must be remembered that 

 every crop removes from the soil one of the elements of plant food to 

 a greater extent than the others. Thus corn removes nitrogen in 

 greater quantities than it removes phosphorus and potash, while 



