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Seedling Growth of Sorghum in Clay-Sand Mixtures at Various Compactions and Water Contents¹

ABSTRACT

Mixtures of kaolinite clay and fine sand fraction from Tripp subsoil (Typic Haplustoll) were prepared with 1.0, 3.8, 7.5, 15, and 30% clay. The clay-sand mixtures were compacted into cylinders at bulk densities of 1.00, 1.25, 1.50, and 1.75 g · cm^-3. The cores were then subjected to matric suctions of 0.15, 0.33, 1.7, and 8.6 bars.

Penetrometer resistance of the cores increased from 0.25 to 68 kg · cm^-2 as the bulk density of clay-sand mixture increased from 1.00 to 1.75 g·cm^-3. Matric suction of the clay-sand mixture contributed much to the increased penetrometer resistance with a correlation coefficient of 0.57.

The elongation of sorghum [Sorghum bicolor (L.) Moench] roots in the cores increased as the clay content increased from 1.0 to 7.5% at all bulk densities when the matric suction was <1.7 bar. Further increase in the clay content decreased the root elongation. The largest negative correlation coefficient (r = –0.65) between root elongation and variables studied was with matric suction. It was considered to be the major factor affecting root length. Penetrometer resistance of clay-sand mixture was critical in relating soil physical conditions to root growth. At a penetrometer resistance of 20 kg·cm^-2 or greater, no root growth in the clay-sand mixtures was observed.

¹ Contribution from the Dep. of Agronomy, Lincoln 68503. Published with the approval of the Director as Paper no. 3556, Journal Series, Nebraska Agr. Exp. Sta., Lincoln, Nebraska.

² Former Graduate Assistant and Professor of Agronomy, respectively.

Received for publication July 16, 1973. Accepted for publication January 14, 1974.