Agriculture Reference
In-Depth Information
Porosity: root death leaves holes
In the early phases of pedogenesis, roots colonise the weathered material of the C horizon
where they create channels that remain open after their death. In calcareous substrates,
Jaillard (1983) noted that limestone may be transformed into calcareous sands as a result
of solubilisation and the further crystallisation of in root cells.
In fully-developed soils, root tips may exert maximum pressures of 0.61 to 1.3 MPa,
with a few values greater than 2 MPa leading to compression of the soil at the point of
root contact. The penetration of small aggregates requires lower axial root growth
pressures than large aggregates and the strength of these larger aggregates may impede
root penetration. Such common plants as pea (
Pisum sativum
), cotton (
Gossypium
hirsutum
) or sunflower (
Helianthus annuus
) may only be able to exert pressures of
0.1-0.3 MPa (Misra
et al.,
1986). Reorientation of particles along the root results in
slight (2-7 %) increases of bulk density (Goss, 1991).
Roots may thus break down large aggregates into small, and create channels that can
have important roles in facilitating water infiltration and gas exchange (Figure IV.42).
