500 INVESTIGATION BY CULTURE EXPERIMENTS 



Probably no agricultural investigations have ever been reported 

 which have brought forth more error and confusion in the public 

 mind than these experiments. 



While they are carried on in part to determine the effect upon 

 wheat yields of continuous wheat culture upon the same land, the 

 information secured only shows that some factor or factors, other 

 than the continuous growing of wheat, have thus far exerted pre- 

 dominating influence upon the production of wheat. 



The figures for nitrogen given in Table 105 are based upon the 

 percentages reported from time to time by Professor Harry Snyder 

 in Minnesota Bulletins 53, 70, and 89, and upon his later statement 

 that all samples have been taken to a depth of 9 inches. 



Thus, in Minnesota Bulletin 53, June, 1897, we read: 



"Plots i, 2, and 3 were 4 rods by 5 rods." 



"On plot No. i, wheat was grown continuously. On plot No. 2, wheat was 

 grown in 1893, an d clover was sown with the wheat; a crop of clover was har- 

 vested in 1894. In the fall of 1894 the clover sod was plowed under, and the 

 next year a crop of wheat was grown, and in 1896 a crop of oats. It is the plan 

 to apply manure at this point and produce a crop of corn, and to follow the 

 corn with wheat and clover, the complete rotation being: (i) wheat and 

 clover, (2) clover, (3), wheat, (4) oats, (5) corn and manure. 



"Plot No. 3. After the wheat crop in 1892, oats were grown, and clover 

 was seeded with the oats, and in 1894 a crop of clover was harvested. The 

 clover sod was fall-plowed and the next year barley was grown. After the barley 

 crop the plot received 1200 pounds of manure, and the next year was seeded to 

 corn, the complete rotation being: (i) oats and clover, (2) clover, (3) barley, 

 (4) corn and manure." 



"In plots Nos. i and 2 there was originally present in the soil .221 per cent of 

 nitrogen, equivalent to 5400 pounds of nitrogen per acre to a depth of 9 inches. 

 After four years' continuous cropping of wheat, plot No. i yielded .193 percent 

 of nitrogen, a loss of .028 per cent, equivalent to an annual loss of 171 pounds 

 of nitrogen per acre." 



"In plot No. 2, where clover has been grown in a rotation, there has been a 

 gain of nitrogen. At the end of the rotation there was .231 per cent nitrogen 

 present in the soil. On this plot clover was grown, and the second growth of 

 clover was plowed under for green manure. The total nitrogen removed in the 

 crops amounted to 178 pounds. Notwithstanding the fact that larger crops 

 have been grown on this plot than on No. i, there has been a gain of 245 pounds 

 of nitrogen in the four years' rotation, in addition to the nitrogen removed in the 

 crops." 



"The soil (of plot 3) originally contained .211 per cent of nitrogen. At the 

 close of the rotation it contained .218 per cent of nitrogen. The amount of 



