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Structure and Its Influence on Tilth of Soils¹

ABSTRACT

The purpose of this study was to determine some of the changes that have taken place in the structure of several Corn Belt soils and its influence on tilth, permeability, volume weight, and percent of pores drained.

Samples of soil were examined in the field to determine the type, class, and grade of structure, direction of natural fracture when lumps were broken, and size and number of visible pores. Six to twelve undisturbed soil core samples 3 inches thick and 3 inches in diameter were taken at random from each plot and depth to determine permeability, volume weight, and percent of pores drained at 60 centimeters tension.

Many surface soils that originally were granular or crumb in structure have changed through cultivation and poor management practices to a fine fragmental or massive structure. With these changes in structure the percolation rate decreased from 8.4 inches to 0.2 of an inch per hour, percent of pores drained was reduced from 9.2 to 3.5, and the volume weight increased from 1.1 to 1.31.

The surface crust was the least permeable layer in the upper 18 inches of the soils studied.

¹ Contribution from the Soil Conservation Service, U.S.D.A., in cooperation with the Illinois Agricultural Experiment Station, Urbana, Ill. Presented before Section I, Soil Science Society of America, State College, Pa., August 29, 1951.

² Soil Scientists, Soil Conservation Surveys Division, Soil Conservation Service. The authors gratefully acknowledge the assistance of many members of the Agronomy Department, Ill. Agr. Exp. Sta. and of the Soil Conservation Service. Special acknowledgment is due F. C. Bauer and his staff, Ill. Agr. Exp. Sta., and L. M. Turk and his staff, Mich. Agr. Exp. Sta., for permission to sample certain experiment plots. The assistance of H. M. Smith, Soil Conservation Service, in taking the pictures is also acknowledged.