THE SOIL 21 



Putting lime on it also will make it fit for plants to 

 grow in. 



THE STRUCTURE OF SOIL 



Qualities of good Soil. In order that plants may grow 

 well, it is most important that the soil should have the 

 power to hold water. It must also be well aired, and 

 must contain the foods that plants require. 



Weigh exactly a kilogram of moist soil. Spread it out on a paper 

 or board in the sun, taking care that none is lost. When it is as dry as 

 it will become, weigh it again, and so learn what per cent more of water 

 was in it than is in air- dry soil. Dry it in or on a stove, and weigh it 

 again. Its further loss of weight shows that air-dry soil is not really dry. 

 Put it in the sun for two hours, and weigh again. It is now heavier, 

 which shows that really dry soil can take up moisture from the air. 



Make these experiments with sand and with clay, and compare the 

 results. 



Note the area of the surface of a potato. Dip it into water, and, 

 after shaking off all the water possible, weigh it. Cut it in two. Is 

 there more potato than there was before ? Has it now more surface? 

 Dip it into water, shake it well, and weigh it again. Cut each piece 

 again and again, noting the effect on the area of the surface, and on the 

 power to hold water. If this experiment is well made, it will prove that : 



(a) The smaller the pieces are, the greater the surface is in propor- 

 tion to the mass. 



(/>) The greater the area of the surface, the more water can be held. 



These conclusions are as true of the soil as they are of the potato. 



KINDS OF SOIL, BY STRUCTURE 



Sand and Gravel. A soil of which as much as 40 per 

 cent is made of particles as large as 0.025 of a millimeter in 

 diameter is called sand. Sand is the coarsest agricultural 



