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5- PREPARATION OF THE: SOIL 



A quantity of potting soil, a very rich black loam, was obtained 

 from the university greenhouse. It had been prepared by piling up 

 turf and allowing the vegetable matter to decompose. After drying 

 to a sufficient degree to render it suitable for handling, the soil was 

 screened through a sieve with one-twelfth inch mesh and mixed with 

 sand, similarly screened, in the proportion of two parts of loam to 

 one part of sand. These two constituents were worked into a per- 

 fectly homogeneous mass, and its capacity for holding water was 

 determined by the following method : 



A cu. dm. of the prepared soil, which weighed i kilo, was dried 

 to constant weight in an oven at lOO degrees C. After the constant 

 weight had been secured, the dry soil was placed on filter-paper in a 

 funnel and water was added in small quantities at frequent intervals. 

 When the soil was uniformly moist and no longer increased in weight 

 after the surplus water had drained off, it was again weighed, and thus 

 the quantity of water necessary to saturate was determined. Soil in 

 this condition was considered to be ioo% saturated. The different 

 percentages of saturation used were computed on the basis of the total 

 amount of water in the saturated soil. 



The following table shows the records of a few typical tests made 

 to determine the capacity of the soil for holding water. 



By exercising a little care, the moisture content of the soil could 

 be adjusted at the beginning of each test so^ that one cu. dm. of soil 

 would weigh i kilo. This was selected as the standard weight and 

 somewhat arbitrarily designated as "normal soil." 



The difference between the weight of the normal soil and the 

 weight ol" the dry soil is the vv^eight of the water in the normal soil. 



The difference in the weights of the dry and the saturated soils 

 is the weight of water necessary to produce ioo% saturation. Know- 

 ing these facts it becomes a simple matter to add water to the normal 

 soil in quantities required to make it any desired per cent, of satura- 

 tion. 



