186 FOOD FOR PLANTS 



dicates a diminishing efBciency for the ammonium 

 sulfate, blood and manure, and a gradual increase in 

 efficiency for the Nitrate of Soda. 



The work shows that when properly used Nitrate 

 of Soda alone as a source of nitrogen may be depended 

 upon to maintain crop yields over a long period, and 

 that a given amount of nitrogen in this form is more 

 effective than an equivalent amount in the form of 

 ammonium sulfate, or organic materials. 



Its effect is to produce larger crops per unit of 

 nitrogen, and these crops, in turn, leave behind in the 

 soil larger crop residues, and with carbonate of lime 

 to aid in their decomposition these furnish a suffi- 

 cient supply of organic matter to keep the soil in good 

 physical condition. 



References. 



(1) Blair, A. W., and McLean, H. C. 1917. Total nitrogen 



and carbon in cultivated land and land abandoned 

 to grass and weeds. In Soil Sci., v. 4, no. 4, p. 

 283-294. 



(2) Coleman, D. A. 1917. The influence of Sodium Nitrate 



upon transformations in soil with special reference 

 to its availability and that of other nitrogenous 

 manures. In Soil Sci., v. 4, no. 5, p. 345-432. 



(3) Lipman, J. G., and Blair, A. W. 1916. Investigations 



relative to the use of nitrogenous plant foods: 

 1898-1912. N. J. Agr. Exp. Sta. Bui. 288. 



(4) Russell, E. J. 1915. Soil Conditions and Plant Growth, 



new ed., p. 83, Longmans, Green and Co., New York. 



(5) Russell, E. J., and Richards, E. H. 1917. The changes 



taking place during the storage of farmyard manure. 

 In Jour. Agr. Sci., v. 8, p. 495-563. 



