88 ELEMENTAKY AGEICULTUEE 



soil dark and rich, but it makes the ground loose 

 and mellow so air can get in. It also enables the 

 soil to hold far more moisture than would be pos- 

 sible without it. Plants, we know, need both air 

 and moisture about their roots, so humus is a valu- 

 able aid to the farmer. 



Soil and Surface Water. How does the soil 

 obtain and keep moisture and give it over to the 

 plants! If we go into the fields after a heavy rain, 

 we notice muddy streams running from the plowed 

 land, carrying off good, fine soil. Part of the water 

 that falls as rain and snow, runs off instead of 

 sinking into the earth. This we call surface water, 

 and it often does much damage to our fields; but 

 much of the water that falls upon the ground sinks 

 into the soil through cracks and holes and between 

 the tiny grains of soil. When the land is dry the 

 farmer likes a slow, steady rain, because it all soaks 

 into the ground to feed plants, instead of running 

 off as surface water and carrying good soil with it. 



Why Clay Soils Are Wet. As the water passes 

 through the soil, each tiny grain of sand and each 

 little particle of earth is covered with a coat of 

 moisture. All through the soil are small holes or 

 open spaces between the^ grains, and into these the 

 water goes. In such fine soil as clay, which packs 

 closely, the spaces are small, and the water cannot 

 pass through rapidly; so it is kept back in holes, 

 open spaces, or puddles. In loose, coarse-grained 

 earth, such as sand, the spaces are large; and the 



