EXPERIMENTS OF THE BUREAU OF PLANT INDUSTRY. 



31 



RELATION OF TESTS SHOWN BY FREQUENCY CURVE. 



The frequency curve (fig. 10) shows that the results secured are 

 not of a mere haphazard nature. Of the total number of experi- 

 ments 46 per cent give results between 92.5 and 107.5 per cent of 

 uncultivated grain in terms of the cultivated. These limits come 

 well within the bounds of experimental error. The general average, 



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Fig. 10.— Diagram showing the yields of uncultivated plats of corn expressed in percentages of yields of 

 cultivated plats for 124 experiments in 28 States. 



therefore, of the whole 124 tests, showing 99.108 per cent as much 

 grain produced on the weeded plats as on cultivated plats, is sig- 

 nificant. 



INTERPRETATION OF THE RESULTS OBTAINED. 



The reasons why uncultivated land kept free from weeds should 

 yield practically as much corn (grain) per acre as that gi^en the 

 most approved modern cultivation are not clear. The results, how- 

 ever, point strongly to the conclusion that the principal object of 

 cultivation is the destruction of weeds. Where the weeds are kept 

 down by some other method cultivation seems to be of no particular 

 advantage. This is contrary to the accepted teaching on this point, 

 and the conclusion is stated only tentatively. There have been 

 abundant experimental results to show that when land is fallow a 

 soil mulch upon it tends to preserve the moisture in the soil. It 

 appears quite possible that when the soil is fully occupied by the 

 roots of a growing crop there is little possibility of moisture from the 

 deeper layers of the soil being drawn by capillary action to the sur- 

 face, where it could be evaporated, for in doing so the moisture would 

 have to thread its way through a maze of roots eager to absorb it. 

 Does it not seem that these roots would themselves play the part| 

 that a soil mulch would play if the roots were not there ? If such is 

 the case, what additional advantage would arise by having a mulch 



257 



