Soils 61 



SOIL STRUCTURE 



Structure refers to the arrangement of the soil particles, 

 which may be wedged tightly together or so arranged that 

 there is considerable air space between. The numerous 

 sizes of particles present in any soil make possible a great 

 difference in structure, particularly in fine soils. Soil 

 tilth, which has such great practical importance, is 

 determined largely by its structure, or the grouping of 

 particles. Soil grains packed tightly together form a soil 

 of poor tilth. When plowed, such a soil breaks up into 

 clods instead of falling apart in granules or floccules. A 

 loose structure gives lines of weakness extending in every 

 direction through the soil. When this condition exists, 

 the soil crumbles readily, but when the opposite condition 

 is found, much work is necessary to put the soil in good 

 condition. The facts that sugar-beets in growing expand 

 greatly and that they require considerable air make very 

 desirable a soil with a good structure. 



IMPROVING SOIL TILTH 



The tilth of a coarse-grained soil cannot be greatly af- 

 fected, since it is always fairly good, but a clay requires 

 constant care to prevent its becoming puddled. Many 

 farmers have learned through experience that by culti- 

 vating a clay soil when too wet, they can so injure the tilth 

 that several years are required to get it back into good 

 condition. Almost anything causing a movement in soil 

 may affect its tilth. Among the common factors are : 

 (1) tillage, (2) the growth of roots, (3) alternate freezing 



