Chemistry Reference
In-Depth Information
Table 2 shows that the mineral content of many crops is typically quite low,
less than 1% by weight for each element. In addition to the major nutrients
shown in Table 2 (P and K), plant growth depends on the availability of minor
nutrients (Ca, Mg, Si and S), and trace nutrients (including B, Fe, Mn, Zn, Se
and others). All of these are ultimately derived from geological sources.
Table 3 summarises the major mineral sources for these elements. In some
cases, minor nutrients especially can be obtained from minerals in which the
element concerned is a major component (for example, the double salts of Mg
and K shown in Table 1, also carbonate minerals or gypsum). In other cases,
element availability depends on the weathering of silicate minerals such as
tourmaline (a complex borosilicate, which supplies B), or silicates containing
Fe, Mg or Ca. Other elements such as Zn and Se may be derived by the
weathering of rocks such as mudstones, in which the mineralogical source of
the element may not be obvious, and in which elements such as Se might be
associated with organic matter.
The availability of nutrients needs to be considered in the scale of crop
production. With the removal of each crop from soil, mineral nutrients are also
d
n
1
r
2
n
g
|
3
Mineral content of selected food and energy crops.
6,7
Table 2
Crop
P
K
Ca
Mg
Si
mg (100 g)
21
mg (100 g)
21
mg (100 g)
21
mg (100 g)
21
mg (100 g)
21
Sugar cane
200
900
200
120
100
Wheat
100
2000
300
200
4000
Potato
37
360
5
17
Leek
44
260
24
3
Apple
11
120
4
5
Banana
28
400
6
34
Table 3
Mineral sources of minor and trace nutrients in plants.
Mineral source
Minor nutrients
Magnesium
Mg
Carnallite, langbeinite, kainite, polyhalite; dolomite
(CaMg(CO
3
)
2
); weathering of Mg-Fe silicate minerals
Calcium
Ca
Lime (Ca(OH)
2
) or limestone (CaCO
3
); gypsum
(CaSO
4
.2H
2
O); dolomite; weathering of Ca silicate
minerals
Sulfur
S
Gypsum
Silicon
Si
Weathering of silicate minerals
Trace nutrients
Boron
B
Weathering of tourmaline
Iron
Fe
Weathering of Fe-Mg silicate minerals
Manganese
Mn
Weathering of Fe-Mg silicate minerals
Zinc
Zn
Weathering of sulfide minerals
Selenium
Se
Weathering of certain mudstones
