THE PRODUCTIVITY OF WOODLAND SOIL 



By J. NISBET, D.CEC. 



In countries where the woodlands have been under more or 

 less systematic management for generations, experience long 

 since showed that the sowing or planting of new crops usually 

 succeeds better on soil that has already been under a tree-crop, 

 and that in sandy localities the growing and trenching-in of 

 lupines is one of the best ways of restoring the exhausted 

 productivity of fallowed portions of nurseries. Experience 

 had also long shown that, as regards natural regeneration of 

 mature timber-crops, the larger and the denser the mature crop, 

 the greater the ease and success with which a new self-sown 

 crop might be raised, owing to the protection thus afforded to 

 the soil against deterioration by atmospheric influences and by 

 a rank growth of herbage and weeds. Thus, while in agriculture 

 large field-crops necessitate crop-rotation and manuring, in 

 forestry close-grown and heavy timber-crops enrich the soil 

 and add to its potential productivity for a following crop of the 

 same species, without any crop-rotation being required in the 

 agricultural sense. 



Originally it was thought (Sprengel's theory) that leaf-mould 

 was the chief source of carbon for plant-food ; but the conclu- 

 sion drawn about the middle of last century by chemists (Liebig 

 and others) from these facts of experience was that the dead 

 foliage annually shed by the trees gives back to the soil, in the 

 form of humus or leaf-mould when decomposed, larger supplies 

 of carbon, withdrawn from the air and assimilated and utilised 

 for elaboration of the sap, than had previously been withdrawn 

 from the soil along with the sap. And as the greater portion of 

 the mineral salts contained in the plant-food are then also 

 returned in the dead foliage, the decomposition of the leaves 

 assists in preparing larger supplies of mineral salts in a soluble 

 form, while the leaf-mould at the same time tends to improve 

 the general quality of the soil by adding to its depth, by making 



clay less stiff and sand more cohesive, and by tending to 



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