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Effect of Soil Hardness and Compaction on Corn Growth¹

ABSTRACT

A Proctor soil plasticity needle was modified so that the hardness of the soil surface in field plots could be measured. The instrument is simple in construction and penetration measurements can be made easily and quickly. Readings were taken before spring plowing, after the 2nd and 3rd cultivation, at first tassel, at the early milk stage, and at the dent stage of corn growth. Surface soil hardness through the growing season was in the order of 3 cultivations < 2,4-D + 1 cultivation < noncultivated (2,4-D only). Surface hardness was correlated with average corn yields for a 3-year period. Data on the number of strokes (force) required to penetrate the soil at 0 to 2 and 4 to 6-inch depths for taking core samples confirmed the penetrometer data. Corn yields varied inversely with the number of strokes. The area traversed by the rear tractor wheel in cultivation is more compact than the area between hills; the 0 to 2-inch depth is less compact than the 4 to 6-inch depth. Plots sidedressed with N generally showed less compaction than nonsidedressed plots. Production and uptake of NO₃-N was in the order of 3 cultivations < 2,4-D + 1 cultivation < noncultivated being inversely correlated with soil hardness. Nitrates accumulated in the tractor wheel area. Apparently, sidedressings of N on soils with poor structure is no substitute for soils in good tilth for increasing corn yields. A soil conditioner chemical (VAMA) adversely affected soil structure, decreasing corn yields. It is suggested there are 5 horizontal and 2 vertical zones of soil hardness or compaction in some cultivated soils.

¹ Contribution from the Department of Soils, The Connecticut Agr. Exp. Sta., New Haven. Presented before Div. I, Soil Science Society of America, St. Paul, Minn., Nov. 10, 1954.

² Chief Soil Scientist and Soil Scientist, respectively. Grateful acknowledgment is made to C. I. Bliss and C. M. Dembiczak for advice and help on statistical analyses, and to D. B. Downs, G. Condouris, and R. M. Hanna for assistance in the field and laboratory work.

Received for publication October 19, 1954.