No. 6. DEPARTMENT OF AGRICULTURE. 461 



alumiua, capable of very tine division and close compaction; the sandy 

 soil, on the other hand, is usually made up largely of quartz, a sub- 

 stance hard and stony, and not easily compacted. The clay, which 

 is more finely divided and does not consist of stony particles, can 

 be compacted so closely as to prevent the rapid escape of moisture, 

 whereas the sandy cannot be readily compacted; it falls away again 

 after pressure and the air and water circulate freely through it. As 

 a broad, general rule, the finer the texture of a soil, the more retent- 

 ive of moisture it is, and the coarser the texture the more readily 

 will the water escape from it. In the first place, then, the greater 

 or less retaining power of soils for w'ater is due to their physical 

 character, and in order to increase or decrease their retentive power 

 their texture should be changed. 



It must be remembered, however, that there is such a thing as 

 a soil being too compact from the standpoint of moisture to plants, 

 because this fineness and compactness prevent the ready penetra- 

 tion of the moisture into it; whereas, the open, porous soil permits 

 its ready penetration, thus the one will, because of its compactness, 

 result in the water flowing off rather than into it, and hence it will 

 not always have as much moisture at a certain definite time after 

 rainfall as the one which is more open and porous, and which per- 

 mits a larger direct absorption and a ready percolation into the 

 lower layers or reservoir below. Therefore, in the study of soil 

 moisture in reference to the plant's needs, improvements of physical 

 character are found to be of service, both in the humid and semi- 

 humid districts, as well as in the arid or semi-arid, where irrigation 

 is practiced; in the case of the easily compacted soil, to enable a 

 greater absorption of that which falls and in the open, porous soil, 

 to cause a greater retention of that which is absorbed. 



The improvement of clay, or finely divided soil, should consist 

 of such operations as will sei)arate the particles, and make the soil 

 more open and porous; this may be accomplished by the introduction 

 into the soil of such substances as will coagulate, or bring together 

 the fine particles, thus making the soil more porous. For example, 

 liming a clay soil does improve its physical character and makes it 

 more absorptive; it seems to have the power of collecting the very 

 finely divided particles and partially cementing them into masses, 

 and making the particles larger, thus making the openings between 

 them greater, which permits a readier penetration into them of 

 water and air. So, too, the introduction of vegetable matter, as 

 coarse manures, influences and improves clay soils in this respect; 

 the absorptive power of the soil is increased by the separation of the 

 particles, not only, but because a substance has been introduced into 

 the soil, which in itself has a greater absorbing power. 



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