Agriculture Reference
In-Depth Information
penetrate below 50 cm. Similarly, figure 3.2 shows that most of the vine roots
in a soil formed on chalky limestone are confined to a shallow depth above the
limestone (unless the limestone is fractured). Deep rooting is also discouraged in
irrigated vineyards if the irrigation strategy is to control water availability in the
top 40 to 60 cm of soil only (see “Controlling the Soil Water Deficit Through
Irrigation,” chapter 4).
The Absorbing Root
Vinesabsorbnutrientsdissolvedinwater,calledthesoilsolution,whichisincon-
tact with the roots. Thus a nutrient such as N, which exists mainly in organic com-
bination, must be released into the soil solution as an inorganic ion—ammonium
(NH
4
+
) or nitrate (NO
3
−
)—to be absorbed by a root. From extensive studies of
higher plants, it is known that the zone of active absorption is about 20 mm long,
located a few millimeters back from the root tip, where there are root hairs (fine
outgrowths from the epidermal cells), as shown in figure 3.3. Root hairs greatly
increase the absorbing surface so that uptake of a nutrient may exceed its rate of
replenishment at the root surface, in which case the concentration around the root
decreases and a depletion zone develops.
Figure 3.2
Darkly stained fine
roots confined to a shallow
Terra Rossa over chalky
limestoneintheBarossaValley
region, South Australia.
