264 CITRUS FRUITS AND THEIR CULTURE. 



Cultivation is beneficial in the following ways : It 

 increases the water-holding capacity of the soil and con- 

 serves moisture, both by allowing rain to sink more freely 

 into it and by checking evaporation. It pulverizes the 

 soil and allows the air to penetrate, thus supplying oxy- 

 gen to the roots. It assists in setting free plant food and 

 makes the soil fine, thus enabling the roots to reach all 

 parts of it. In cultivated soils, decomposition and nitri- 

 fication go on more readily and if the materials are pres- 

 ent from which nitrogen can be set free, its liberation 

 takes place more rapidly than if the soil be left unculti- 

 vated. 



Most of the moisture in tillable soil is held as a mi- 

 nute film surrounding the soil particles. It necessarily 

 follows that the more numerous the soil particles in a 

 given space, i. e., the smaller they are, the greater will 

 be the water-holding capacity of the soil, because the 

 total surface area of all the particles increases as they 

 are reduced in size. And it is true, within certain limits, 

 that the water-holding capacity of a soil increases as the 

 size of the particles diminishes. If, however, the particles 

 become too small, they may become too closely packed, and 

 thus this object of cultivation will be defeated. This con- 

 dition is not likely to occur in light, sandy soils as a re- 

 sult of cultivation. The size of the particles can be re- 

 duced by cultivation by breaking up masses which may 

 have become more or less cemented together, and the water- 

 holding capacity may be thereby increased. 



The opening and loosening of the soil permits the 

 rain to penetrate. If the surface of the ground becomes 

 hard and compact, the water will run over the surface or 

 collect in puddles and disappear by evaporation. In either 



