GRAIN FARMING 21 



also make air passages. Such openings also help to drain the 

 soil, permitting the water to run down through to the sub-soil. 



Humus, again, acts like a sponge, absorbing and holding the 

 water so that the plants can get it. 



Water. — There is no more important element in a fertile or 

 productive soil than water. Water is necessary for plant 

 growth. Any soil without water is worthless. 



Water, so necessary for plant growth, is in part held in 

 solution by the humus in the soil. In the main, however, it is 

 held in the soil in the form of a thin layer of water around each 

 soil particle. The finer the particles, therefore, the more 

 water the soil will hold. 



Water is also held between soil particles by what is known as 

 capillary attraction. By capillary attraction, also, the water 

 from beneath is brought to the surface to maintain the supply 

 as the plants draw it from the soil on the surface. Capillary 

 attraction is well illustrated in the lamp wick which draws 

 oil from the bowl of a lamp to the burner. 



Anchorage.^ — The soil also serves as an anchorage for plants. 

 The roots of plants, trees included, descend into the soil be- 

 tween and below the heavy soil particles, and those hold the 

 plants upright. Sometimes, however, when the wind is high, 

 and the soil is loose, trees or other tall and heavy plants are 

 blown over. 



Good Soil and Poor Soil. — The value of the soil depends 

 entirely upon the amount of plant food it contains. A good 

 soil contains much and a poor soil little. Plants need as food, 

 not only the elements brought into the soil by water and air, 

 but the elements composing the rock or soil particles them- 

 selves. Different soils are made up of different elements and, 

 therefore, are adapted to different kinds of crops. Different 

 crops need different foods just as do different animals. 



A good soil, also, is one that is made up of fine particles. 

 The finer the particles of soil, the more will the surface be 

 exposed to the solvent action of water, acids, and alkalies, 

 and the more easily will food in the soil particles be set free. 

 A soil made up of particles that are easily decomposed, there- 

 fore, is better than one whose particles are difficult of decompo- 

 sition. Some poor soils will grow profitable crops for one. 



