20 FERTILITY AND FERTILIZER HINTS 



be compact enough to support the plant in an upright position, 

 but if it is too compact the young plant has to overcome a great 

 deal of resistance in securing its food. 



Plants Must Have Room. — Only a certain number of plants can 

 be grown successfully on a given space of land. We have only 

 to examine the root development of mature plants to learn the 

 spreading tendency of plants. If plants are too crowded, im- 

 perfect development is the result. The roots of plants spread 

 somewhat and the distance apart is regulated to some extent by 

 the available plant food, the nature of the plant and the tillage 

 of the soil. In the foreign countries more plants are usually 

 grown on a given area than in America but the land is perhaps 

 more thoroughly tilled, because land is high in price and labor 

 cheap, while in America land is comparatively cheap and labor 

 high. In w-ell tilled soils roots go deeper and do not spread so 

 much as in soils in poor condition. 



Plants Require Oxygen. — A soil that is too compact will not per- 

 mit of the free circulation of air. When air is excluded from 

 the soil, free oxygen which is absolutely necessary for growth 

 is excluded. It has been shown that when air is not freely sup- 

 plied to plants they become sickly and growth is retarded. When 

 a soil becomes water-logged, plants w^ill not grow and if the 

 condition continues the plants will die. Some plants will grow 

 in water but the water must be fairly free from soil so as to be 

 able to absorb and diffuse oxygen from the air. It has been 

 found that 40 to 60 per cent, of the water holding capacity of 

 soils is the best amount and 80 per cent, is injurious. 



Drainage. — Good crops cannot be grown unless the land is well 

 drained, either naturally or artificially. A certain amount of 

 water is essential for crops, but a water-logged condition must 

 be avoided to secure good results. 



Capillary Water. — In the preceding chapter we learned that 

 crops use a great deal of water, the clover crop for example 

 exhales as much as 1,096,234 pounds per acre. Crops usually 

 rely on capillary water for their supply of this constituent. The 

 upward movement of water in the soil is termed capillary 

 inoisture, or capillary water, and is caused by the surface ten- 



