86 SOILS 



dent that the nitrogen supply, instead of being seriously 

 disturbed, more likely is preserved and it may not be out of 

 the range of possibilities to suppose that the normal aver- 

 age is ever increased : a feature quite opposite in effect to 

 that of depletion. Certainly, land occupied by clover two- 

 fifths of the time during a fifty-year period preserves its 

 producing power. Who will say it does not even increase it? 

 The help that comes from the subsoil. Since roots 

 have come into the range of observation and study, we 

 know that they seek deeper pastures than the surface foot 

 allows. Roots go to a depth of two, three, four and often 



INCREASING THE NITROGEN WITH LEGUMES 



A crop of soy beans that are bringing nitrogen into the boil and at the same 

 time producing a high protein feed 



ten or twelve feet. Consequently, the supplies that come 

 to plants are not solely from the surface foot : for plants 

 get food wherever their roots go, wherever the root hairs 

 find mellow earth into which they may search. 



This subsoil contribution, therefore, is a large one, and 

 one that, in a great measure, influences the potential sup- 

 ply of plant food, commonly supposed belonging to the 

 surface soil, but which is a not-inconsiderable factor of the 

 entire food-furnishing possibilities of the land. 



