November, 1908.] 



457 



SCIENTIFIC AGRICULTURE. 



WATER AND THE SOIL. 



Rapid-growing plants require large aud 

 regular supplies of water. Plants use 

 from 300 to 900 times their weight of 

 water during growth. This water is 

 pumped up through the roots and eva- 

 porated through the leaves and in pass- 

 ing up through the plant carries with it 

 such food as may be in solution in the 

 soil. As a rule, most agricultural plants 

 will not live in standing water because 

 the water keeps the air from the roots. 

 Rice is an exception to this rule. 



The water that plants use is that 

 which remains in the soil after drainage 

 has taken place. For example, if you 

 take a bucket of sand and immerse it in 

 water, all the spaces between the grains 

 of sands are filled with water. Now 

 punch a few holes i u the bottom and 

 allow drainage to go on for three or 

 four days. Y"ou say all the water is out 

 of the soil, yet it is not all out, for there 

 is still a film of water around each grain 

 of sand just as a piece of rock would be 

 covered with water after dipping in 

 water and allowing it to drip for a few 

 minutes. This is called capillary water. 

 The small root hairs, which are the 

 active feeding roots of the plant, 

 surround these grains of sand and take 

 up this water by what is known as 

 " osmosis." The control of this water is 

 a very important factor in growing 

 crops and improving soil. 



Good agricultural soils hold capillary 

 water equal to about 30 per cent, of their 

 weight. Plants are not able to use this 

 water after it has dried out to about 

 12 per cent., so that when the soil is in 

 the best condition for plant growth only 

 about 60 per cent, of the total moisture 

 is available to the plant. During the 

 dry season loss of water takes place by 

 evaporation at the surface of the ground 

 as well as through the leaves of the 

 plant. Fortunately for the roots of the 

 plant this water tends to maintain an 

 even balance ; that is to say, when a 

 portion of the soil dries out, this water 

 moves toward the dry place from the 

 point of greatest moisture. An ex- 

 ample of this is when the surface dries 

 and water from below comes up to take 

 the place of that lost by evaporation. 

 When water has been taken out of the 

 soil by the roots of plants other water 

 moves towards this spot and of course 

 carries with it soluble plant food, pro- 

 vided there is any in the soil, 

 58 



The rapidity of movement of capillary 

 water depends upon the size of the soil 

 particles and the proportion of fine and 

 coarse particles. Water will move more 

 rapidly through coarse sand than 

 through clay, but as the water is held in 

 the soil in the form of a thin film around 

 the soil grains, and there being more 

 surface of the soil grains in a cubic foot 

 of fine clay than in the same quantity of 

 sand, there will be more water moved in 

 the clay soil in a given time than in the 

 sand, although it moves more slowly. 

 Hence clay soils do not suffer from 

 drought as much as sandy soils. 



Most agricultural soils, when composed 

 of the proper mixture of sand and clay, 

 have a tendency, under normal condi- 

 tions, to form small clusters of soil 

 particles, just as small particles of sand 

 tend to cling to larger ones, thus bring- 

 ing about the best mechanical condition. 

 This mechanical condition is destroyed 

 when the soil is stirred while wet. This 

 is called "puddling." Soil so handled, 

 when exposed to the direct rays of the 

 sun, becomes very hard. This condition 

 is known as " baking," and simply means 

 that the granular structure has been 

 destroyed and the soil particles cemented 

 together by drying. " Soils allowed to 

 bake in this manner are very difficult to 

 put in good condition again. The 

 mechanical condition may be improved 

 by the use of shade crops, such as velvet 

 beans, etc The shade allows the slow 

 action of capillary water to restore this 

 cluster condition. Working when the 

 land is in proper condition will also tend 

 to improve the soil. Freezing is the 

 method used in cold climates. 



The movement of steepage water 

 through the soil is governed largely by 

 the mechanical condition of the soil. A 

 soil composed of fine clay holds water 

 very much as a jug, and if sufficient 

 drainage is not supplied the plants 

 suffer from the staguant water. When 

 the soil is open and porous this does not 

 occur because the water goes on down 

 through and does not keep the air out of 

 the soil. But when water is allowed 

 to run through the soil too freely it 

 washes out the soluble plant food that 

 has been liberated by natural methods. 

 Soils that are too compact need 

 drainage. 



A controlling factor in soils, so fat- 

 as moisture is concerned, is humus. 

 Humus is partially decayed leaves, 

 grass roots, or other organic matter in 

 soils which, on account of the great 



