EXERCISE 11 

 CAPACITY OF SOILS TO HOLD MOISTURE 



Object. To determine the capacity of different types of 

 soils to hold moisture and to study the effect of organic 

 matter on the moisture-holding capacity of the soil. 



Explanation. Soil water is held in the soil partly as 

 a thin film surrounding the soil particles and partly as an 

 accumulation of water in the pore spaces of the soil. If 

 a soil is saturated with water, all its pore space will be filled, 

 and the capacity of a soil to absorb water will be determined 

 by the amount of its total pore space. If the water is allowed 

 to drain away from the saturated soil, the free water will 

 escape. After the free water has percolated away, the water 

 which remains will represent the amount of film water that 

 the soil will hold. 



Different types of soils differ in the amount of pore space 

 they contain and in the amount of surface exposed around 

 the soil particles, and therefore in the amount of free and 

 film water that they can hold. Other things being equal, 

 the soil having the smallest-sized particles will have the 

 greatest amount of pore space and will hold the most water. 



Organic matter affects the water-holding capacity of the 

 soil. Those soils of the same texture supplied with the most 

 organic matter will absorb and hold the most water. Or- 



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