502 INVESTIGATION BY CULTURE EXPERIMENTS 



the third four-year period also there was a slight gain of nitrogen, and at the end 

 of twelve years, the soil contained about 7800 pounds per acre, showing that 

 where clover was grown once in four years in a rotation with grains, and one 

 dressing of farm manure was applied to the corn at the rate of eight loads per 

 acre, the nitrogen content of the soil has been maintained unimpaired." (See 

 pages 193 to 195 in Minnesota Bulletin 89.) 



In his excellent and widely used text and reference book on 

 " Fertilizers," Doctor Voorhees, Director of the New Jersey Ag- 

 ricultural Experiment Station, makes the following statements: 



"Another source of natural loss of nitrogen is its escape from the soil as gas 

 into the atmosphere. This is due to the oxidation of the vegetable matter, or 

 to 'denitrification,' which takes place very rapidly where soils rich in vegetable 

 matter are improperly managed. The possibilities of loss in this direction are 

 strongly shown by investigations carried out at the Minnesota Experiment 

 Station on ' the loss of nitrogen by continuous wheat raising' (Minnesota Bulle- 

 tin 53). The results of these studies show that the total loss of nitrogen an- 

 nually was far greater thaa the loss due to cropping. In other words, by the 

 system of continuous cropping, which is universally observed in the great 

 wheat fields in the Northwest, there was but 24.5 pounds of nitrogen removed 

 in the crop harvested, while the total loss per acre was 171 pounds, or an excess 

 of 146 pounds, a large part of which loss was certainly due to the rapid using up 

 of the vegetable matter by this improvident method of practice. Whereas, on 

 the other hand, when wheat was grown in a rotation with clover, the gain in 

 soil nitrogen far exceeded that lost or carried away by the crop." 



These statements faithfully represent the teaching of Minnesota 

 Bulletin 53, except as to the manner in which the nitrogen escapes. 

 With the more recent accumulated information concerning soil 

 bacteria, to which Doctors Voorhees and Lipman of the New Jersey 

 Station have largely contributed, a revision of Voorhees' " Fer- 

 tilizers" probably will not ascribe any large part of the loss to 

 denitrification. 



In his own text-book on " Soils and Fertilizers," published in 

 June, 1905, Professor Snyder makes the following statements 

 (page 112): 



"A rotation of wheat, clover, wheat, oats, and corn with manure will leave the 

 soil at the end of the period of rotation in better condition as regards nitrogen 

 than at the beginning. These facts are illustrated in the following table : 1 



1 Minnesota Agricultural Experiment Station Bulletin No. 53. 



