Agriculture Reference
In-Depth Information
4
How the Soil Supplies Nutrients
Essential and Nonessential Elements for Grapevines
4.1
Most plants need 16 elements to grow normally and reproduce. Some of these el-
ements are required in relatively large concentrations, ideally
1,000 mg/kg
(0.1%) in the dry matter (DM); these are called
macronutrients
(table 4.1). The
others, called
micronutrients
(table 4.1), generally are required in concentrations
100 mg/kg DM (0.01%).
Of the essential elements, C and O are supplied as CO
2
from the atmosphere,
whereas H and O are supplied in H
2
O from the atmosphere and water sources.
Chlorine is also abundant in the air and oceans as the Cl
ion. Winds whip sea
spray containing Cl, Na, Mg, Ca, and S into aerosols to be deposited by rain on
the land or as “dry deposition” on vegetation. Nitrogen as N
2
gas in the atmo-
sphere enters soil-plant systems primarily by “biological fixation” (section 4.2.2.1),
although small amounts are also deposited as NH
4
and NO
3
ions from the air.
Cobalt (Co) is essential for biological N
2
fixation in legumes and blue-green al-
gae. For the remaining essential elements, the major source is minerals that weather
in the soil and parent material.
Another term frequently used is
trace element
, which can include both essen-
tial and nonessential elements. A trace element normally occurs at a concentra-
tion
1,000 mg/kg in the soil. There are three categories of trace elements:
1. The essential
micronutrients
Cu, Zn, Mn, B, and Mo, which are beneficial
at normal concentrations in the plant (ranging from 0.1 mg/kg for Mo to
100 mg/kg for Mn) but which become toxic at higher concentrations. Iron
is the only micronutrient that is not strictly a trace element.
2. Elements such as chromium (Cr), selenium (Se), iodine (I), and Co that
are not essential for plants, but are essential for animals.
3. Elements such as arsenic (As), mercury (Hg), cadium (Cd), lead (Pb), and
nickel (Ni), which are not required by plants or animals and are toxic to
either group at concentrations in the organism greater than a few mg/kg.
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