MINNESOTA SOIL INVESTIGATIONS 501 



nitrogen removed in the crops during the four years amounted to 204 pounds. 

 The gain in nitrogen has been at the rate of about 40 pounds per acre." 



Four years later, in Minnesota Bulletin 70, May, 1901, we find 

 the following statements: 



"Plots Nos. i and 2 contained, at the beginning of the experiments in 1892, 

 .221 per cent of nitrogen, while plots Nos. 3, 4, 5, and 6 contained .211 per 

 cent. It is estimated that an acre of the soil of plots Nos. i and 2, to a depth 

 of 9 inches, would contain approximately 7700 pounds of nitrogen, while the 

 remaining plots would contain approximately 7400 pounds. At the end of the 

 first four years of continuous wheat cultivation, plot No. i contained .193 per 

 cent of nitrogen ; a loss of .028 per cent, equivalent to an annual loss of 1 71 

 pounds of nitrogen per acre. At the end of the second period of four years, 

 the soil contained .173 per cent of nitrogen. 



"At the beginning of the experiment in 1892, plot No. 2 contained .221 per 

 cent of nitrogen. At the end of eight years, after the removal of five crops of 

 wheat, two of clover and one of oats, or six grain crops and two clover crops, the 

 soil contained .198 per cent of nitrogen." 



"On plot No. 3, oats, clover, barley, and corn have been grown. The soil 

 of this plot originally contained .211 per cent of nitrogen. At the end of eight 

 years the soil contained .198 per cent of nitrogen." (See pages 254-256 in Min- 

 nesota Bulletin 70.) 



In Minnesota Bull^in 89 (January, 1905) we find the following 

 statements : 



"While 21.7 percent of the soil nitrogen was lost during the first eight years 

 of continuous wheat culture, only 5.71 per cent was lost during the four years 

 following." 



"On plot No. 2 a rotation consisting of wheat, clover, wheat, oats, and corn 

 and manure has been followed, with some modifications because of climatic 

 conditions. The soil of this plot contained originally about the same amount 

 of nitrogen as plot No. i, namely, 7700 pounds per acre to a depth of one foot. 1 

 At the end of twelve years the soil contained 6725 pounds." 



"The soil of plot number three originally contained about 7400 pounds per 

 acre of nitrogen. At the close of the first period of four years, the soil showed 

 a slight gain in nitrogen, and at the end of eight years, a slight loss. During 



1 On page 380! Minnesota Bulletin 102 (September, 1907) a correction note states 

 that this should read: "to the depth of three fourths of one foot, " and consequently 

 it must be assumed that the "7700 pounds" should read "5400 pounds" (less 

 than 75 per cent), and that corresponding corrections should be made throughout. 

 According to the data (5400 pounds for .221 per cent) the soil of an acre to a depth 

 of 9 inches would amount to about 2,450,000 pounds, which agrees with Professor 

 Snyder's statement that the soil weighed about 75 pounds per cubic foot (page 9, 

 Minnesota Bulletin 53). C. G. H. 



