INFLUENCE OF CULTIVATION AND WEED KILLERS ON SOIL STRUCTURE AND CROP YIELD

Abstract

The effect of using 2,4-D, flaming, and oil spray and their indirect effect on soil structure vs. killing weeds by the usual cultivation methods for corn and carrots were studied. Heavy rains early in the season and subsequent hot dry weather resulted in soil crusting which reduced soil nitrification. The corn plants showed definite N starvation, although the carrots were not visibly affected. An avg. increase of 40 bu. of corn per acre was obtained for plots cultivated for the control of weeds as compared with those treated only with 2,4-D at the rate of 1.5 lbs. of Na salt spray per acre. Flaming the corn produced a decrease of 9 bu. of corn per acre. This small difference in yield may have been due to breaking of the soil crust by a single cultivation. In one season the soil in the tractor-wheel area in cultivated corn plots was packed more than in non-tractor-wheel areas. In the 0-2-inch depth, a blue-grass sod area had 68% higher macroporosity, 29% higher total porosity, and 25% lower volume wt. than the alley turn-around areas; corresponding values for the cultivated non-tractor-wheel area were 35, 9, and 1%, resp. Percentage decreases in macroporosity from the 0-2- to the 4- to 6-inch depths for the blue-grass sod, cultivated non-tractor wheel, and alley areas obtained were 47, 15, and 3%; for total porosity 28, 7, and 0; and for volume wt. 25, 7, and 0%, respectively. Differences in porosity and volume wt. among the various treatments at lower depths were small. Soil structure differences in the 0-2- inch depth alone were found to be more significant statistically than when all sampling depths (0-2-, 4-6-, 6-8-, 12-14-inch) were considered together. The 0- to 2-inch depth showed less packing effect in the tractor-wheel area in the carrot than in the corn plots. Also, higher statistically significant values for soil physical data were obtained for corn than for carrots. This was probably due to differences in wts. of tractors used.