MINNESOTA SOIL INVESTIGATIONS 503 



"CONTINUOUS WHEAT CULTURE 



Nitrogen in soil at beginning of experiment 0.221 per cent 



Nitrogen at end of 5 years' continuous wheat cultivation . . 0.193 per cent 

 Loss per annum per acre (in crop 24.5, soil 146.5) .... 171 pounds 



"ROTATION OF CROPS 



Nitrogen in soil at beginning of rotation 0.221 per cent 



Nitrogen at close of rotation 0.231 per cent 



Gain to soil per annum per acre 61 pounds 



Nitrogen removed in crops per annum 44 pounds 



"It is to be regretted that in the cultivation of large areas of land to staple 

 crops, as wheat, corn, and cotton, the methods of cultivation followed are such 

 as to decrease the nitrogen content and crop-producing power of the soil when 

 this could be prevented." 



Unquestionably the greatest practical problem that confronts 

 the average American farmer is to maintain the humus and nitro- 

 gen content of the soil, 1 and the author cannot be true to the stu- 

 dent and neglect to present the determined facts in a matter of so 

 vital consequence to American agriculture. It will be noted that 

 the data just quoted relate only to the first four years (not five 

 years or twelve years) of these Minnesota experiments, where no 

 manure had been used. As a matter of fact, the published bulletins 

 show that wheat (not corn) was grown on plot 2 the fifth year. 

 The subsequent data show, however, that during the second four 

 years (presumably with manure added) there was a loss of nitrogen 

 from plot 2 amounting to .033 per cent (.231-. 198), or about 800 

 pounds per acre (counting only 2,450,000 pounds of soil for a depth 

 of 9 inches) , and during the same four years the data for the other 

 rotation, with manure applied, show a loss of 490 pounds of nitro- 

 gen per acre from plot 3. 



The only point the author would emphasize is that these Min- 

 nesota investigations have not yet furnished sufficient data to 



1 It is a very simple matter to maintain or materially increase the phosphorus 

 content. One ton of raw rock phosphate, costing from $7 to $10 (depending on 

 distance of shipping), and containing, say, 250 pounds of phosphorus, will supply 

 more of that element to an acre of land than would be removed in 12 years if the 

 average crops were 100 bushels of corn (grain only removed), 100 bushels of oats, 

 50 bushels of wheat, and 4 tons of clover. 



