ORGANIC MATTER AND SOIL MOISTURE 153 



74. Content of organic matter. Organic matter, 

 especially in the form of humus, has a larger capacity 

 for moisture than has the mineral portion of the soil. 

 Aside from the fact that such material has a large inher- 

 ent moisture capacity, and that in proportion to its 

 amount in the soil it increases the water capacity, 

 no exact figures can be given. The moisture content 

 of such material varies with the stage of decay, as well 

 as the general physical properties of the material. The 

 following figures compiled by Storer illustrate this 

 capacity. 



Per cent of 

 water retained 



1. Humic acid extract from peat 1,200 



2. Non-acid humus prepared from peat 645 



3. Ordinary vegetable mold 190 



4. Peat \ 201-309 



5. Garden loam, 54 per cent clay, 7 per cent humus. 96 



6. Dark Illinois prairie soil 57 



7. Mucky soil (weighing 30 pounds per cubic foot) . 75 



Besides its inherent capacity, organic matter affects 

 the moisture capacity through its influence on soil 

 structure. In clay it produces a desirable condition 

 of granulation and therefore increases the absolute 

 moisture capacity. And its addition to sand has. a similar, 

 though smaller effect. This is illustrated by the follow- 

 ing figures, obtained by Detmer, as quoted by Storer, 

 which resulted from the mixture of sand and muck. 

 It will be noted that in proportion as muck is substi- 

 tuted for an equal weight of sand, the water capacity 

 of the mixture is increased, as is well shown by the 

 ratio in the last column. 



