VERTICAL FARMING 13 



to have its particles arranged in much the same way as the sand, 

 with the important exception that each is pressed close to its 

 neighbor and bound there by cohesion, by adhesion, by some 

 other substance present, by interlocking corners of the parti- 

 cles, or by other means. When such a soil is disturbed it does 

 not fall apart like sand, but remains in close, hard lumps or 

 clods. In these soils we have the extremes of structure the 

 open structure, or the individual grain and the dense structure 

 or arrangement of the pubbled soil. A well- 

 tilled plat of clay or loam will be found to 

 have an entirely different structure. Here 

 the fine particles of clay, silt and sand are 

 bound together in little groups or crumbs. 

 These crumbs or granules can be easily de- 

 tected by picking up a handful of the soil and 

 gently breaking it apart. These crumbs DIAGRAM OF SOIL 

 lie close against other crumbs, but unless GRANULES 

 poorly handled in cultivating they do not be- 

 come sealed together. This is the ideal structure of a soil, and it 

 is toward the formation of such granules that we should direct 

 our attention, especially in the heavier soils. When such a soil 

 is cultivated wet, the pressing action of the plow or harrow 

 tends to force the particles closer together and to form the 

 undesired puddled structure; but if the moisture content is just 

 right, the same plowing will tend to make the granulation still 

 better. Additions of humus material, and, on some soils, of 

 lime, help also. 



Such a crumb structure in a soil brings about most of the 

 benefits and advantages of both a sand and a clay. It drains 

 well, and because of its open structure warms up well in the 

 spring. The openness permits easy and good plowing. The 

 fine particles absorb and hold the large amount of water needed 

 for the crop, and if properly cultivated to preserve this moist- 

 ure, will tide heavy crops over longer periods of rainless times. 

 Another great advantage of the crumb or open structure of 

 clay and loam soils is that they allow the roots to grow quickly 

 to -great depths. This affords the plant a much larger amount 



