THE SOIL WATER 89 



If you have no graduate, weigh the pots before and after 

 pouring, and note the differences. Either of these experi- 

 ments will show that the sandy soil holds least, the clay soil 

 holds most, water. 



To understand this, dip a pebble into water, and notice 

 that you cannot shake all the water off it. It remains moist 

 until it dries in the air, or is wiped. Every tiny grain of 

 soil is like the pebble, for it will take and hold a film of water. 

 But now take a piece of wood, best a cube of an inch, and 

 estimate its surface. Split it once, and see how much the sur- 

 faces measure now. In the case of an inch cube, two square 

 inches of water-holding surface have been added by splitting. 

 Split again, and yet again, and you will see how rapidly 

 the surface increases. In the case of soils, this shows that 

 the finer soils naturally have more water-holding surface. 

 Therefore, of course, the clay soils will hold more water than 

 the sandy. 



If the manure, or leaf mold, has been of good quality, and 

 pretty finely ground, it will hold more water than any of the 

 soils. This is because, unlike the rock particles, it does not 

 merely hold the water on its surface, but soaks it in like a 

 sponge. To show the difference, take a pot of sandy loam, 

 and another in which the loam has been mixed with one 

 quarter of its amount of manure. Then, as before, find the 

 amount of water which these two will hold. 



We can conclude from all this that the finer the particles 

 of a soil, the better it is able to supply plants with water. 

 (Other reasons may interfere, of course, to show why, for 

 certain plants, clay soils may not be the best after all.) We 

 can also conclude that manure added to a soil will enable it 

 better to hold water. 



Let us try our first experiment over again, first plugging 

 the holes in the pots, and then pouring in the water until it 



