THE SOIL 25 



pouring it into the air. For this reason they are sometimes 

 planted in wet pastures to dry them so that grass will grow there. 



Care of Soil Moisture. As agricultural plants need much 

 moisture, farmers in most sections find it important to conserve, 

 or save, and utilize soil moisture as fully as possible. The methods 

 used depend largely on soil, climate, and weather conditions. A 

 soil's water-holding capacity is increased by deep plowing, and by 

 the addition of manures and of humus. Loss by evaporation 

 can be checked by -stirring the surface so as to form a soil- 

 mulch, or layer of loose soil, an inch or two thick. This sepa- 

 rates the particles so that they cannot lift the moisture from the 

 soil and subsoil to the surface, where it is carried off by evapora- 

 tion. 



Irrigation. In some sections the rainfall is scanty or uneven 

 and the ' water table ' is far from the surface. Even when the soil 

 moisture is properly cared for, there is not enough to supply crop 

 needs. This may be the case with soils which are rich in plant food. 

 Are these to be given over to barrenness ? It has been found wise 

 'and practicable to ir'ri gate these lands, that is, to supply them 

 with water by a system of reservoirs and canals connected with 

 streams. Lands thus reclaimed are often wonderfully productive. 

 There are millions of acres of land in the western part of the United 

 States which need ir ri ga'tion. 



Drainage. While some soils are barren for lack of water, 

 others are useless for agricultural purposes on account of its excess. 

 We have already seen tnat some plants can live without soil in water 

 supplied with plant food. Does it, then, seem contradictory to say 

 that plants can have too much water ? In fact, it is not that they 

 have too much water, but that they have too little air. Plants, like 

 animals, need 6x'y gen, and this oxygen they take in chiefly through 

 their roots. Like animals, they are drowned and die if deprived 



