332 ECOLOGY 



Effect of liming clay soils. The liming of soils, especially 

 in clayey districts, is common. Why is this done ? Clayey 

 soils hold much water, and are therefore badly aerated, and 

 organic acids formed from the decay of plants tend to 

 accumulate and make the soil ' sour '. The addition of 

 lime lessens these defects. Two very simple experiments 

 will show us the effect of lime on clay : 



(i) Stir up a little clay in water ; the very fine particles 

 remain indefinitely in suspension. Add to the muddy 

 liquid a little lime-water and note its effect. The particles 

 run together in fluffy-looking masses and soon sink to the 

 bottom, leaving the liquid clear. 



(2) Bend two pieces of gauze each into the shape of a 

 saucer or shallow cup and line them with wet clay. Pour 

 lime-water into one and tap-water into the other, and place 

 each on the top of a tumbler. Does the clay hold both 

 liquids equally well ? The tap-water does not percolate, 

 but the lime-water permeates the clay readily and changes 

 its properties. It becomes less sticky ; it has clotted and 

 become more porous, and it is no longer able to hold water. 

 Other salts and mineral acids have a similar effect, and as 

 lime also neutralizes the organic acids in a sour soil, we see 

 that its effects are threefold : it renders the stiff, unwork- 

 able clay more workable, improves its drainage, and, as the 

 farmer says, ' sweetens it ' by neutralizing the organic acids. 

 Clay is also rendered more pervious by mixing with humus. 



State of the water in the soil : capillarity. How water 

 ascends in the soil. Previous experiments have shown 

 that water ascends higher in loam than in sand, and 

 higher still in clay. Microscopic examination shows that, 

 of the three, sand consists of the coarsest particles, clay the 

 finest, while loam is intermediate. The larger the grains, 

 the greater will be the spaces between them. Will this 

 in any way affect the power of a soil to absorb water, and 

 if so, how ? 



