No. 6. DEPARTMENT OF AGRICULTURE, 299 



Secondly, the finer the soil particles are to a certain extent, the 

 •rrealer will be their power of absorbing water. There is a limit to 

 which the soil particles ought to be reduced, as it has been fouTul by 

 experiment that when a certain degree of fineness is reached, the 

 absorptive power decreases without any further pulverization. It is, 

 however, improbable that the average farmer will ordinarily ever re- 

 duce his soil to so fine tilth. The trouble generally lies in the op- 

 posite direction. 



Closely connected with the absorptive power of soils is the power 

 they have of retaining the water they absorb. This power, it is 

 readily seen, has an important bearing upon the fertility of the soil. 

 As a considerable interval often occurs between periods of rainfall, 

 soils that are to support a luxuriant plant-growth must be able to 

 store up their water supply against periods of drouth. While the 

 fineness of the soil particles has an important influence upon the 

 absorptive power, so it has been found to have an important bearing 

 upon the rate at which evaporation takes place. Evaporation is 

 greatest when the soil particles are compact together. The stir- 

 ring of the surface soil has for this reason an important influence 

 in lessening the amount of evaporation. As a general rule, the 

 greater the absorptive power the greater is its retentive power; for 

 soils that most largely absorb water are most reluctant to part with 

 it. While these proi>erties are necessary for a fertile soil, they 

 may in some cases be possessed by soils to too great an extent, hence 

 the necessity for the drainage. The soil that is unable to throw off 

 an excess of water is damp and cold and does not admit of proper 

 tillage. The pores are choked up and the proper circulation of air 

 is rendered impossible. A stiff, clay soil often offers a familiar ex- 

 ample of over-retentiveness. Experiments have shown that plants 

 have not the means of exhausting the water from a retentive soil to 

 such an extent as in a non-retentive soil. The presence or absence 

 of the above properties suggests a word or two in regard to how 

 these defects may be to a certain extent remedied artificially. If 

 the absorptive power of a soil is rendered greater by the presence 

 of organic matter it stands to reason that if the organic matter be 

 increased the absorptive power of that soil will also be increased, 

 of which we will have more to say later. Where a soil is too reten- 

 tive till drainage probably presents the best means of remedying 

 such defect. Of this subject we cannot here speak at length. 



During periods of drouth the hygroscopic power of soils is an mi- 

 portant feature. By hygroscopic power is meant the power soils 

 liave of absorbing moisture from the air. The moisture which ex- 

 ists in the air in the form of vapor, is to a greater or less extent ab- 

 sorbed by the soil as air comes in contact with the ground during soil 



