HOW TO MAINTAIN SOIL NITROGEN 325 



organisms act. Hence, we must conclude that alfalfa not only 

 feeds closer on the soluble nitrates of the soil, but it also makes a 

 greater drain upon the insoluble nitrogen of the soil by increasing 

 its nitrifying powers and would therefore deplete the soil if the 

 entire crop be removed, more readily than would other crops a 

 conclusion which is borne out by the direct analysis of the soil. 



The analysis of a great number of Utah soils which have grown 

 various crops for a number of years some of them having been 

 into alfalfa or wheat for upward of thirty years revealed the 

 fact that almost invariably the alfalfa soil contained less total 

 nitrogen than did the wheat soil. The average for a great number 

 of determinations made from alfalfa soils was 7232 pounds per 

 acre of total nitrogen, while the average for a great number of 

 wheat soils was 7398 pounds. These are average results from a great 

 number of determinations made on adjoining alfalfa and wheat soil 

 and they clearly indicate that in ordinary farm practice the alfalfa 

 is making just as heavy a drain upon the soil nitrogen as is the 

 wheat. 



Hence, from a consideration of the yields obtained in crop rota- 

 tion, the relative quantities of nitrogen obtained from the atmos- 

 phere and the soil by the alfalfa, the feeding and stimulating effect 

 of the alfalfa upon nitrification, and finally the actual quantity of 

 total nitrogen remaining in the soil after wheat and legumes^ we 

 must conclude that the legume does not increase the nitrogen of 

 a common agricultural soil even in the arid region where the 

 nitrogen is low when the entire crop is removed. 



This conclusion does not, however, mean that crop rotation 

 should not be practised, for there are many reasons why crop rota- 

 tion commends itself to the careful farmer, but it must not be used 

 and the legume removed with the intention of maintaining soil 

 fertility. This may appear to be an unfortunate conclusion, but 

 it is just the reverse, and if its teachings be heeded it means a 

 fertile soil and an economic gain to the farmer from the system of 

 farming which it requires him to adopt. 



How to Maintain Soil Nitrogen. There are two practicable 

 methods of maintaining the nitrogen content of the soil. (1) 

 Planning systems of crop rotations with legumes, the legumes 

 being plowed under and allowed to decay, thus furnishing nitrogen 

 to the succeeding crop; (2) practising a combined system of crop 

 rotation and livestock farming. 



Three tons of alfalfa contain 150 pounds of nitrogen, all of 

 which we could assume came from the atmosphere. Assuming 

 the quantity found in the roots as coming from the soil, this is the 

 equivalent of the nitrogen found in the grain and straw of 75 

 bushels of wheat. If the alfalfa is plowed under some of the 

 nitrogen would be lost to the growing plant in the processes of 

 decay and leaching, but that the total nitrogen of the soil may 



