90 AGRICULTURAL BACTERIOLOGY. 



chemical form these other nitrogen portions are left need not 

 concern us, and, indeed, is not yet accurately known ; but they 

 constitute the nitrogenous element of the humus. It is upon 

 these nitrogen compounds left in the soil that the next gener- 

 ation of plants must feed. Now it is certain that much of the 

 nitrogenous material resulting from decomposition is in a con- 

 dition in which it is not available for plant life. Even the am- 

 monia salts are only very slightly used by plants unless further 

 modifications occur in them, and the other nitrogenous bodies 

 in the soil are not directly used by plants. In other words 

 the decomposition processes going on in the soil do not leave 

 the nitrogen in a form in which the next crop of plants can 

 utilize it. 



If the soil in almost any locality be analyzed it will be found 

 to contain some nitrogen. If the soil be fertile it will com- 

 monly contain a considerable quantity of nitrates or ammonia 

 salts. But there are other soils in which the yield of crops is 

 small from the fact that the plants seem to be nitrogen-starved. 

 These barren soils will not yield good crops unless supplied 

 with a considerable amount of nitrogen as a fertilizer. Yet 

 these same soils may contain plenty of nitrogen. Upon an open 

 hillside or a meadow we may find the land very poor for sup- 

 porting vegetation, and yet its soil when analyzed may yield 

 large quantities of nitrogen. In such a soil the nitrogen is sim- 

 ply locked up in the humus in a form useless to plants. Thus it 

 frequently happens that a large part of the gyyg^p is, at the end 

 of decomposition, held in a form not available for ordinary vege- 

 tation, and plants growing in such a soil will be nitrogen-starved 

 although growing in the midst of plenty of nitrogen compounds. 

 Such soils might become highly fertile if there should be some 

 agency for unlocking these nitrogenous compounds, freeing the 

 nitrogen from its stable relations and producing compounds of a 

 nature to be assimilated by plants. Until we have discovered 

 such forces the nitrogen problem is not solved. When we 



