292 DRY-FARMING 



come from without. The nitrogen question will 

 undoubtedly soon be the leading one before the 

 students of dry-farm fertility. A liberal supply of 

 organic matter in the soil with cultural methods 

 favoring the growth of the nitrogen-gathering bac- 

 teria appears at present to be the first solution of the 

 nitrogen question. J^ieanwhile, the activity of the 

 nitrogen-gathering bacteria, like azotohacter, is one 

 of our best explanations of the large presence of 

 nitrogen in cultivated dry-farm soils. 



To summarize, the apparent increase in produc- 

 tivity and plant-food content of dry-farm soils can 

 best be exi^lained l\y a consideration of these factors : 



(1) The intrinsically high fertility of the arid soils; 



(2) the deej) feeding gr(_)und for the deep root systems 

 of dry-farm crops ; (3) the concentration of the plant 

 food distributed throughout the soil by the upward 

 movement of the natural precipitation stored in the 

 soil ; (4) the cultural methods of dry-farming which 

 enable the weathering agencies to liberate freely and 

 vigorously the ])lant-food of the soil grains; (5) the 

 small annual crops; (6) the plowing under of the 

 header straw, and (7) the activity of bacteria that 

 gather nitrogen chrectly from the air. 



J\Iethods of conserving soil-fertility 



In view of the com].iaratively small annual crops 

 that characterize dry-farming it is not wholly im- 



