62 THE ESSENTIALS OF AGRICULTURE 



64. Causes of poor physical condition. There are several 

 causes of poor physical condition. Working the soil when it 

 is too wet breaks down the crumb structure and compacts the 

 particles. If plowed wet, hard clods form when it dries. A heavy 

 beating rain falling upon a soil that has been worked very fine 

 often brings about a compact structure at the surface, and if 

 such soil dries rapidly, a hard crust will form (Fig. 32). When 

 the supply of organic matter is greatly reduced, as is the case 

 with much old and improperly farmed land, it becomes compact 

 and loses its friable condition, or its good tilth. 



65. How a poor physical condition may be improved. The 

 things which tend to bring a compact soil back into condition 

 are (i) fall plowing in the Northern states, by which the soil 

 is exposed to the winter's freezing ; (2) working into the soil 

 organic matter, such as stable manure, or green manure ; 1 

 (3) better drainage ; (4) the addition of large quantities of slaked 

 lime ; (5) seeding the land to grass for three or four years. 

 The alternate wetting and drying of a soil resulting from re- 

 peated rainfall is also important in loosening a compact soil. 



The things which tend to keep soils in good physical condition 

 are ( I ) working them only under proper moisture conditions ; 

 (2) maintaining the supply of organic matter ; (3) thorough 

 drainage. Soils of fine texture are difficult to keep in a friable 

 condition. Sandy soils or sandy loams can be plowed earlier in 

 the spring and worked with much more water in them than can 

 clay loams or clay soils. Similarly, soils containing much organic 

 matter, as sod land, can be worked earlier and with more water 

 in them than can stubble land. The ease with which a soil can 

 be tilled is therefore a matter both of texture and of condition. 

 The ease of tilling a soil is sometimes more important than 

 its fertility. 



66. Color as an indication of value of a soil. A black soil, 

 with few exceptions, is a fertile soil. The color indicates the 

 presence of plenty of organic matter, and this usually means an 



1 A green-manure crop is a crop, such as rye, clover, or peas, turned under 

 for the purpose of enriching the soil in organic matter. 



