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Effect of Particle Surface Roughness on Mechanical Impedance of Coarse-Textured Soil Materials¹

ABSTRACT

Packing energy required to increase bulk density in coarse-textured soils is influenced by particle surface roughness, i.e., by interparticle friction. It was, therefore, hypothesized that particle surface roughness would influence soil resistance to movement of a cone penetrometer, because soil bulk density is increased in the zone surrounding the penetrometer tip during its advance. The cone index (C.I.) was calculated for all penetrometer measurements, and C.I. was compared in both disturbed and undisturbed coarse-textured soil material, with each soil having a unique particle surface roughness as determined by the dense soil angle of repose measurement. For soil materials with similar particle size distributions and bulk densities, C.I. increased as particle surface roughness increased.

The role of particle surface roughness in tillage pan formation and in root growth restriction is discussed. It is suggested that, due to poorer aeration during rainy periods and higher mechanical resistance during drier conditions, tillage pans formed in soil materials having smoother-surfaced particles will be more restrictive to root growth compared to those pans formed in soil materials having rougher-surfaced particles. Consequently, among soils having root-restricting tillage pans, the greater enhancement of rooting depth due to subsoiling would likely occur on soils with smooth particles compared to soils with rough soil particles.

¹ Contribution from the Dep. of Soil Science, North Carolina State Univ. Paper no. 6,788 of the Journal Ser. of the North Carolina Agric. Res. Service, Raleigh, NC 27650.

² Asst. Professor, Professor, Research Assistant, and Research Technician, respectively, North Carolina State Univ., Raleigh, NC 27650. The Senior Author is currently with the Dep. of Agron., Iowa State Univ., Ames.

Received for publication February 2, 1981. Accepted for publication July 24, 1981.