Articles
THE EFFECT OF SOIL PHYSICAL CONDITIONS ON ROOTS AND UPTAKE
Growth and production by plants is the result of metabolic processes, which require a steady provision of material.
The materials derived from the soil consist mainly of water and minerals.
But one must be aware of the fact that numerous soluble organic compounds of low to intermediate molecular weight may also be absorbed (Wiersum, 1974). Whether these compounds, e.g. fulvic and humic acids, are of any intrinsic value for the plant is mostly still uncertain.
Absorption of these soil-derived compounds is performed by the root system.
For the rate of supply to be adequate transport in the soil towards the absorbing roots and the flux of substances through the soil-root interface must be sufficiently fast.
Also the transverse transport from the root surface to the xylem should be adequate as well as the movement along the xylem upwards (Liu et al,. 1978). In this introduction we will restrict our attention to the flux of substances through the soil-root interface.
The amount of substances provided by this flux across the soil-root interface is the product of absorbing root surface and rate of entry into the root.
In discussing the influence of soil physical conditions, an attempt will be made to elucidate the manner in which they affect these two aspects of the uptake process.
In discussing the performance of the root system, we must be aware that the growth and functioning of the roots are closely linked to that of the shoot.
There are many reciprocal relationships and numerous feedback systems.
In this respect the roots are dependent on the shoot for supply with assimilates, but they themselves produce hormones, in variable amounts, which regulate shoot activities.
Although root systems vary greatly in their potential development, depending on species and cultivar, we have very little information of what their growth pattern would be in a uniform medium with unimpeded growth.