460 ANNUAL, P.EI'ORT OF THE Off. Doc. 



and as the plants grow the moisture is gradually drawn to the 

 surface by the influence of capillarity, and the amount necessary 

 for full production is obtained, and while its original source is the 

 rainfall, the immediate supply to the plant is derived from that which 

 has fallen a considerable time previous to the period of growth of 

 the plant. 



Wet and Dry Seasons. 



In countries and States where the year is divided in respect to 

 rainfall into a rainy season and a dry season, the above considerations 

 are well understood, and methods of practice which shall result in 

 the conservation of moisture are of the greatest importance. In 

 what are called the humid regions of the country, the crop does 

 depend in many cases more largely upon the immediate rainfall than 

 upon that which has fallen previously, and in these regions there 

 are seasons when periods of drouth intervene, which make it neces- 

 sary that a study should be made of the causes which contribute to 

 the rapid escape of water from the soil, and thus make the supplies 

 insufficient to furnish plants with what they need during the grow- 

 ing season. 



The Loss of Water From Soils. 



Water escapes from the soil by rising to the surface, where it is 

 vaporized, absorbed by the atmosphere and carried away by the 

 wind. The escape of water is, therefore, principally due to capil- 

 larity, for as the dry air passes over the surface of the earth, as 

 well as circulating through the surface area, it absorbs all the mois- 

 ture it comes in contact with; more moisture then rises from below 

 to take its place, and so on until only the hygroscopic water is left 

 in the surface, or within the reach of the roots. 



It has been observed that all soils in the same climate do not 

 become dry at the same rate. That is, one soil will remain wet, 

 another reasonably moist, and another absolutely dry, as far as 

 plant growth is concerned, and these in many cases may all be 

 located on the same farm. These differences are due to the char- 

 acter of the soil, or the particles that constitute it, which have a 

 greater or less power of retaining or holding fast to the moisture 

 contained in it. Or, in other words, the character and texture of 

 the soil influences the rate at which the water will escape. By char- 

 acter of the soil is meant its composition, both in reference to the 

 minerals that are contained in it, as well as the size of the particles 

 of which it is composed, or its texture. 



A clay soil will hold water more tenaciously than a sandy soil. 

 The clay soil is composed largely of a mineral known as silicate of 



