LOSSES AND GAINS BY THE) 



277 



Loss of Various Cropping Systems. When a soil is continu- 

 ously cultivated to the same crop, such as wheat, and all the 

 material removed, it decreases in productiveness, until it reaches 

 a low crop level, at which production may be maintained for a 

 number of years. 



If the soil receives fertilizers or manure continuously, the losses 

 of plant food will be greater, and the soil will adjust itself to a 

 higher level of productiveness as long as conditions are so main- 

 tained. 



Distribution of the Losses of Nitrogen. At Rothamsted, study 

 was made of the disposition of the nitrogen added to the soil dur- 

 ing a period of 50 years. Analyses were made of soil from 

 different plots treated differently, at the beginning and end of 

 the period, of the crops, and of the water from tile drains. 

 Of 86 pounds nitrogen added per acre per year in 50 years, the 

 disposition seemed to be as follows : 



DISPOSITION OF NITROGEN, PER YEAR. 1 



The maximum loss took place with ammonium salts alone. The 

 amount of the total loss was estimated by adding the amount of 

 nitrogen in the soil at the beginning to the total amount added as 

 a fertilizer and subtracting from this the amount present in the 

 soil at the end of the fifty years. The nitrogen lost may have 

 passed into the ground water below the drains. In this work, 

 only 17 per cent, of the nitrogen was used by the crop. It is 

 quite possible that with smaller applications of nitrogen, much 

 smaller losses and much better utilization of the nitrogen, would 

 have taken place. The excessive amounts of nitrogen used 

 caused heavy losses. 



1 Bulletin 106, Office Exp. Sta., U. S. Dept. Agr. 



