484 NOTES ON THE SOIL, 



Examine the soil after it has settled ; the coarser material at the 

 bottom is sand, above this is finer material consisting chiefly of clay 

 (the finer grains remain suspended in the water, making it cloudy), and 

 on top of the water floats a little decomposed vegetable matter (humus). 



(b) Place a pailful of water on a table and dip into it a piece of 

 rubber tubing, to act as a siphon. Get a number of tumblers ; into one 

 place a handful of garden soil, and stir it up with water to form a 

 thick paste. Suck water through the tube to start the siphon-action, 

 then direct a weak current (by pinching the tube) into the tumbler 

 containing the soil, having a tumbler below to catch the overflow. The 

 weak current will carry over the finest grains When the water runs 

 clear, have another tumbler ready, and let a stronger current come 

 through the tube. Notice the time which the grains of different sizes 

 take to settle and leave the water in each tumbler clear. 



Sand consists of grains of various sizes. Sandy soils are called 

 "light" because they are easy to work, though a cubic foot of dry 

 sand weighs about 110 Ibs., while a cubic foot of dry clay weighs only 

 70 or 80 Ibs. ; sandy soils are more open, more porous, warmer, and 

 drier than clay soils. A pure sand contains little but insoluble silica 

 in the form of quartz-grains, hence it acts practically as a sterile 

 medium, though when watered with dilute nutrient solutions plants 

 are able to grow in it. Sandy soils formed from crumbling rocks 

 which have not been much washed by rain-water will, however, contain 

 most of the elements necessary for the food of plants. 



Sandy soils, which are too porous and have not sufficient cohesion 

 for plants to get a good grip of them, are improved by any additions 

 tending to greater consistency and retentiveness, such as the ploughing 

 in of green crops, large quantities of farmyard manure, vegetable refuse 

 of all kinds, powdered clay, black mud from the bottom of ponds, the 

 cleanings of ditches, etc. Evaporation from sandy land during hot 

 weather is largely checked by regular cultivation and the maintenance 

 of a surf ace- mulch of loose soil an inch or two in depth, or by mulching 

 with two or three inches of manure. 



Clay. In clay the grains are smaller than most of those in 

 sand, but they have a tendency to cling together and become cemented 

 into composite grains. In drying, clay tends to form a hard compact 

 mass, impenetrable by the roots of plants ; when wet it tends to 

 become sticky and waterlogged. Clay soils are said to be "cold" 

 because they contain more water than sandy soils, but all good soils 

 contain more or less clay, which is richer in plant-food than any other 

 part of the soil. The presence of clay not only increases the power of 

 retaining water, which is very deficient in pure sand, but also increases 

 the percentage of phosphoric acid, potash, and magnesia. 



Clay is also of great service to plants in "fixing" various substances 

 essential for plant-food, that is, in combining with these substances 

 and preventing them from being too readily washed out of the soil by 

 rain-water. The presence of clay increases the power of retaining 



