FERTILITY 



175 



however, be attained, and, on the poorer soils, probably a 

 profitable return could not be obtained, unless the materials 

 lost by the sale of produce, and in other ways, were replaced 

 from external sources. In short, it is generally necessary 

 and advisable to add plant foods, as well as to restore a 

 large proportion of what is taken out of the soil by the 

 crops. Plant foods may be added to the soil directly, or 

 they may be purchased in the form of food for animals and 

 be afterwards added to the soil in the form of farmyard 

 manure. There are thus two points at which materials 

 may be introduced into the cycle to compensate for the 

 losses by sale of vegetable and animal produce. The cycle 

 remains as before, and the importation of extraneous 

 matters may be indicated in the following manner : 



Soil 



Crops 



Muck * 



It is evident that if plant foods are purchased and added 

 to the soil in the form of what are known as fertilisers, 

 or artificial manures, larger crops can be produced on the 

 same land ; a larger amount of vegetable and animal pro- 

 duce may thus be sold, and there will be more to go back 

 to the land. If, instead of raising larger crops by means 

 of artificial manures, a quantity of food for animals be 

 purchased, more stock can be kept; the animals retain, 

 permanently, only a small proportion of the fertilising 

 ingredients of the food ; the remainder goes back to the 

 land, and larger crops may be produced. 



Essential Difference between Purchased Fertilisers and 

 Farmyard Manure. There is thus a great fundamental 



