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Therefore the role played by black-fallow in dry steppe localities 

 is of the highest importance, because it is only by its application that 

 deeper soil horizons, even those inaccessible to the roots of perennial 

 plants, can be made moist. 



These horizons inaccessible to annuals having received water, hold 

 it and form a permanent humid layer. Than water sinks deeper than the 

 root-inhabitable layer in wet years, whatever plants are under cultivation; 

 and it does the same in average years as regard moisture, when certain 

 plants like potatoes and flax are cultivated. This surplus of useful water 

 percolating beyond the limit of the root-inhabited layer goes towards the 

 formation of a permanent humid layer. 



