50 



20-inch disk working to a depth of five or six inches, was harrowed 

 once July 20, the teeth of the harrow penetrating the very loose soil 

 to a depth of about four inches, and was planted July 22. Plot 3 

 had the same treatment except that a 16-inch disk was used, working 

 to a depth of not more than three or four inches, and it was then har- 

 rowed to a depth of three inches only. Plot 4 was treated precisely 

 like Plot 2 except that it was harrowed a second time with a toothed 

 harrow after three diskings with the 20-inch disk. Plot 5 was also 

 treated like Plot 2 except that the three diskings were doubled, the disk 

 lapping over half its width upon the ground disked the preceding 

 round. It was thus not only stirred more thoroly than the other 

 plots, but more deeply also, since the overlapping half of the disk cut 

 to a depth of six or seven inches. 



These various treatments enabled us to analyze the effects of a 

 preparation of the soil which included disking three times in compari- 

 son with those of another preparation like it except that these three 

 diskings were omitted ; the comparative effects of three double disk- 

 ings and three single diskings; and the effects of three stirrings of the 

 soil with a 16-inch disk as compared with those of a 20-inch disk. We 

 were also able to compare the effects upon the ants' nests in the field 

 of plowing to a depth of four inches and of six inches respectively. 



In Plot 1, plowed four inches deep, 52 nests were examined of 

 which only 8 were completely turned out by the plow, the 44 others 

 being only partly turned out or merely uncovered, while in the four 

 other plots, plowed to a depth of six inches, 376 nests were found, of 

 which 321 were completely turned out, 55 being partly thrown out or 

 merely uncovered. Stated in percentages, 15 per cent of the ants' 

 nests were wholly thrown out at four inches, and 85 per cent at six 

 inches. 



In a similar comparison made in the fall of this same year in the 

 Galesburg field on a larger scale, still more positive evidence was ob- 

 tained that the four-inch plowing in fall does not effectively reach the 

 nests of the corn-field ant. Two hundred nests were especially ob- 

 served in ground plowed to a depth of four inches, and 300 in ground 

 plowed six inches deep, and it was found that only half of 1 per cent 

 of the nests were wholly overturned by the four-inch plowing, 99^^ 

 per cent being partly overturned or merely uncovered, while in the six- 

 inch plowing 58 per cent were overturned completely and 42 per cent 

 were partly so. To break up and scatter the nests of the ants the 

 ground should be plowed at least six inches deep, and seven inches 

 would be safer. 



