The penetration of clays by fine probes and root tips

Abstract

Penetration tests were conducted in a saturated clay using fine probes and pea radicles. The point resistance encountered by fine probes, Qp, was related inversely to the rate of penetration of the probe. The resistance increased exponentially with decreasing voids ratio, ew,; at any given value of ew more resistance was offered by clay that had been remoulded than by finely aggregated clay. When radicles grown through a bed of soil crumbs encountered cores of moderately consolidated saturated clay, they merely indented the clay before turning and growing horizontally. When their tips were inserted in channels that had been formed in the cores, they were unable to penetrate directly through moderately consolidated remoulded clay (ew < 1.10), but grew along horizontal fissures that developed in the clay. No fissures developed in the aggregated clay, and the radicles were unable to elongate at ew < 0.81. The results of the penetration tests are interpreted with the aid of a mathematical model taking into account the strength and compressibility of the clay. In addition, multiple exposure photography was used to show the paths of motion followed by clay particles near the tip of the probe and the radicle. Qualitative information on friction between the root tip and the clay was obtained by matching the local deformation of the clay around the root tip with the deformations produced by probes of known roughness. The root tips tended to compress the clay 'cylindrically', whereas the probe tips compressed the clay 'spherically'. There appeared to be little friction between the root tip and the clay.

Root penetration profiles of wheat and barley as affected by soil penetration resistance in field conditions

“…This was in close agreement with a number of studies using reconstructed soils (Taylor and Gardner 1963;Taylor etal. 1966;Camp and Lund 1968;Cockroft et al 1969). Other authors (Grimes et al19'15;Gerard et al 1982; Ehlers et al 1983;Yapa et al 1988;Vepraskas and Wagger 1989) have reported higher values.…”

Variation in penetrometer resistance with soil properties: the contribution of effective stress and implications for pedotransfer functions

“…5) shows a relatively uniform distribution of points around the 1:1 line although the model may be underpredicting SMR slightly at observed SMRN6000 kPa. However, the RMSE values were still relatively large when one considers that the rate of root growth may approach zero at a SMR of 2000-3000 kPa (Taylor et al, 1966;Cockroft et al, 1969). Becher (1998) has found large variability in SMR between aggregates extracted from the same soil.…”

Influência do cultivo contínuo da cana-de-açúcar em latossolos amarelos coesos do estado de Alagoas: propriedades micromorfológicas

“…A pulverização dos horizontes superficiais, em decorrência do cultivo contínuo e sob condições de chuva, propicia a eluviação da argila dispersa, levando à conseqüente obstrução dos poros (Helalia et al, 1988;Fuller et al, 1995). Podem também ocorrer penetrações de argila através de finos canais secundários formados pelo avanço do crescimento de raízes de plantas com sistema radicular fasciculado (Cockroft et al, 1969), como é o caso da cana-de-açúcar no presente trabalho. 2.…”