LEGUMES AND SOIL FERTILITY 



179 



Crop 



Milligrams Nitric Nitrogen Produced in 100 gms. Soil tn 



2 J Bays 



Average 





Spring 



Midsummer 



Fall 





Alfalfa 



Oats 



Corn 



Potatoes 



Fallow 



3'^S 

 2.40 



2.18 



3.00 



1.30 



7.4« 

 4.00 



3^50 



15-55 

 5.50 



3.08 

 3.00 

 1.48 

 5.60 

 2.48 



4.56 



3'^ 



2.38 

 8.04 



3-^9 



The quantity of nitrates produced in the alfalfa soil is greater 

 than that produced in either the oat, corn, or fallow soil. This 

 increased nitrification is also noted in alfalfa soil the year after 

 the alfalfa is plowed under. This accounts in a measure for the 

 increased yield obtained the year following the plowing of an 

 alfalfa field. Therefore, we can conclude that alfalfa stimulates 

 ammoniiiers and nitriiiers so they render available faster the nitro- 

 gen of the soil. This would indicate that the legume depletes 

 the soil of its nitrogen more readily than the non-le'gume, as it is 

 the nitrogen already combined in the soil on which the nitrifying 

 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 were removed more readily than would other crops — 

 a conclusion which is borne out by the direct analysis o£ the soil. 

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

 various crops, some of them having been into alfalfa or wheat for 

 upward of thirty years, revealed the fact that almost invariably 

 alfalfa soil contained less total nitrogen than did wheat soil. The 

 average for a great number of determinations made on alfalfa 

 soils was 7,232 pounds per acre of total nitrogen, while the aver- 

 age for a great number of wheat soils was 7,398 pounds. 



These are average results from numerous determinations made 

 on adjoining alfalfa and wheat soil, and they clearly indicate that 



