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II. Status in World Soils
MICRONUTRIENTS IN CROP PRODUCTION
grown in various parts of the world (Cakmak, Sari et al., 1996; Fageria, 2000a;
Galr˜ao, 1999; Graham et al., 1992; Grewal and Graham, 1999; Mandal and Mandal,
1990; Martens and Lindsay, 1990). It has been estimated that 3.95 billion ha of
the world’s ice-free land area is subject to mineral stresses for plants, with 14%
of this area being subject to potential micronutrient stresses (Gettier et al., 1985).
The reasons for micronutrient deﬁciencies are that these elements have not usually been applied regularly to soils through fertilization. Furthermore, increased
crop yields, loss of micronutrients through leaching, liming of soils, decreased
use of manures compared to chemical fertilizers, and increased purity of chemical
fertilizers without micronutrient additions have contributed to accelerated exhaustion of available micronutrients in soils. Hidden micronutrient deﬁciencies may
be more widespread than has generally been suspected. Potential micronutrient
deﬁciencies/toxicities associated with major soil groups (Table I), common soil
Potential Micronutrient Deﬁciencies or Toxicities Associated with Major Soil Groupsa
Mollisols (Aqu), Inceptisols,
Entisols, etc. (poorly drained)
Mollisols (Aridis) (Udolls)
Mollisols (Rendolls) (shallow)
(Natric) (high alkali)
Aridisols (high salt)
Fe, Mn, Zn
Cu, Mn, Zn
Fe, Mn, Zn
Co, Fe, Zn
Cu, Fe, Mn, Zn
Cu, Fe, Mn, Zn
Modiﬁed from Baligar and Fageria (1999); Clark (1982); Dudal (1976); S. W. Buol, North
Carolina State University, Raleigh; H. Eswaren, USDA-NRCS, Washington, DC.
FAGERIA et al.
Major Soil Minerals Containing Micronutrientsa
Chalcopyrite—CuFeS2; Bornite—Cu3FeS4; Digenite—Cu9S5;
Hematite—Fe2O3; Goethite—FeOOH; Magnetite—Fe3O4
Braunite—(Mn, Si)2O3; Psilomelane—BaMg9O18·2H2O
From Chesworth (1991), Dana and Dana (1997), Krauskopf (1972), and Mortvedt (2000)
minerals containing various micronutrient elements (Table II), and concentration
ranges of micronutrients in soils and plants (Table III) have been provided to help
deﬁne where micronutrient problems might occur.
Concentrations of B in soils range from about 2 to 100 mg kg−1 (mean of
10 mg kg−1) and generally occurs as H3BO3/B(OH)3 (Goldberg, 1993). Soils
Essential Micronutrients for Plant Growth, Principal Forms Absorbed, Concentration Ranges in Plants and Soils, and Persons Demonstrating
Essentiality in Plants
in plantsa (mg kg−1)
in soilb,c (mg kg−1)
H3BO3; BO3−; B4O72−
Bennett (1993) and McBride (1995).
Alloway (1995a) (critical level above which toxicity is likely).
Kabata-Pendias and Pendias (1992).
Demonstration of essentialityd
T. C. Broyer et al. (1954)
A. L. Sommers, C. B. Lipman, and
G. MacKinney (1931)
J. Sachs (1860) Knop.
J. S. McHargue (1922)
D. I. Arnon and P. R. Stout (1939)
A. L. Sommers and C. B. Lipman (1926)
P. H. Brown et al. (1987)
FAGERIA et al.
formed from igneous rock contain less B than soils formed from marine sediments. Soils derived from granite, igneous, and acidic rocks and metamorphic
sediments are often poor in B (Gupta, 1979). Low B soils are usually strongly
weathered (Acrisols, Podzols, Ferralsols), coarse textured (Arenosols), and shallow (Lithosols) (Shorrocks, 1997). In acidic rocks and metamorphic sediments,
B occurs in tourmaline minerals and is not readily available to plants. Boron adsorption usually increases with increasing soil solution pH, temperature, ionic
strength, and nature of adsorbed cations (Goldberg, 1993, 1997). The amount of B
adsorbed in ﬁne-textured soils usually increases with enhanced clay contents. For
example, montmorillonitic clays normally adsorb greater amounts of B than illitic
clays (Goldberg and Glaubig, 1986). Competitive anion effects on B adsorption
increased in the order of P > Mo > S even though the competitive effect was low,
indicating that B adsorption sites are generally speciﬁc for B (Goldberg, 1997;
Goldberg, Forster, and Lesch et al., 1996). The B-adsorbing surfaces in soils are
commonly Al and Fe oxides, Mg hydroxides, clay minerals, Ca carbonates, and
organic matter (OM). The distribution of B between soil solution and adsorption
surfaces is affected by clay mineral types, content, and speciﬁc surface areas, mineralogy of sand/silt fractions, sesquioxides, SOM content, pH, ions on exchange
sites, and salinity (Elrashidi and O’Conner, 1982; Evans and Sparks, 1983; Gupta
et al., 1985). These soil factors also affect the retention of B in soils (Gupta, 1993).
The availability of B is commonly reduced in soils high in Al oxides (Bingham
et al., 1971) as well as in volcanic ash soils (Sillanpăaaă and Vlek, 1985). In soil, B is
normally present as nonionized molecules and easily lost by leaching. In arid and
semiarid regions particularly, B toxicity can be of major concern (Gupta, 1979).
Chlorine is ubiquitous in soils and occurs in aqueous solutions such as Cl−. Soil
Cl is not tightly held by soil-exchange sites and is readily leached. Chlorine is
commonly added to soil with manures and fertilizers(KCl), rainfall, sea spray, and
irrigation waters (Needham, 1983).
Copper is mostly found in silt and clay fractions of soil and usually present
in carbonate fractions in alkaline soils and in Fe oxide fractions in acid soils
(Shuman, 1991). Concentrations of Cu in soils range from about 2 to 100 mg kg−1
(mean of 30 mg kg−1) (Mortvedt, 2000). Crops grown in soils developed from
sand, sandstones, acid igneous rocks, and calcareous materials often exhibit Cu
deﬁciency, but deﬁciencies are not generally found on plants grown in clays and
in soils formed from basic rocks (Jarvis, 1981a). In the United States, soils formed
from weathered bed rocks have high Cu, whereas soils formed in the lower Atlantic
coastal plains have low Cu (Kubota, 1983). Organic, peat, and muck soils generally
have low amounts of labile Cu (Oplinger and Ohlrogge, 1974). When histosols
are brought under cultivation, plants commonly exhibit Cu deﬁciency, which has
been termed as a “reclamation disease” (Welch et al., 1991).
Iron is the most abundant of the micronutrients in the lithosphere (Mortvedt,
2000). Soil concentrations of Fe range from 7000 to 500,000 mg kg−1 (mean of
MICRONUTRIENTS IN CROP PRODUCTION
38,000 mg kg−1 or 3.8% in soil) (Lindsay, 1979). Most Fe in the Earth’s crust is in
the form of ferromagnesium silicate. Iron is precipitated as Fe oxides or hydroxides
during weathering, and small fractions of Fe are incorporated into secondary silicate materials (Schwertmann and Taylor, 1977). Iron deﬁciency occurs commonly
on plants grown in calcareous and noncalcareous coarse-textured soils, especially
in arid/semiarid regions. However, Fe deﬁciency can also occur on plants grown in
acid soils. About 4.8 million ha of land west of the Mississippi river in the United
States (intermountain region) is prone to Fe deﬁciency in “Fe-inefﬁcient” crops
(Mortvedt, 1975). Alkaline, calcareous, and acidic sandy soils in Florida have also
been prone to Fe deﬁciency on citrus (Welch et al., 1991). Iron deﬁciency has also
been closely related to Ca carbonate equivalency and soluble salts in soil (Franzen
and Richardson, 2000). High soil pH, SOM, CaCO3, HCO3−, and Ca contents have
also been related to decreased Fe acquisition in some plants (Kăoseoglu, 1995). Iron
deciency also occurs in various regions of Europe, east India, Bangladesh, and
in most Mediterranean and west African countries (Welch et al., 1991). Low Fe
soils and Fe-deﬁcient crops have been reported for certain areas of Malta, Turkey,
Zambia, and Mexico (Sillanpăaaă , 1982), Indonesia (Katyal and Vlek, 1985), several
Central and South American countries (Leon et al., 1985), and in south Australia,
Victoria, and western Australia (Donald and Prescott, 1975). Excess Fe (toxicity)
has been reported on rice grown under ﬂooded conditions in acid soils of China,
Vietnam, Thailand, Burma, Bangladesh, Sri Lanka, Malaysia, Phillippines, and
Indonesia (Vose, 1982). Kang and Osiname(1985) also reported Fe toxicity on
plants grown in the acid soil belt of equatorial Africa, which includes Senegal,
Gambia, Liberia, and Sierra Leone.
Manganese is the 10th most abundant element in the Earth’s crust. Soil Mn
concentrations range from about 20 to 3000 mg kg−1 (mean of 600 mg kg−1)
(Lindsay, 1979). Soil Mn appears in primary and secondary minerals, is sorbed onto
mineral and OM surfaces, and incorporated into soil organisms and in soil solution.
Soils derived from crystalline shales and acid igneous rocks have low reducible
Mn, and soils derived from basalt, limestone, and shale commonly have high Mn
(Glinski and Thai, 1971). High extractable Mn has been reported for Inceptisols
and Vertisols and low extractable Mn has been reported for Ultisols and Oxisols
(Lombin, 1983). Labanouskas (1966) and Reuter et al. (1988) grouped the world
soils with less than adequate levels of available Mn as (i) shallow, peaty, marsh, and
alluvial soils developed from calcareous parent materials; (ii) calcareous soils with
poor drainage and high OM, calcareous black sands, and calcareous grassland soils
recently brought into cultivation; (iii) soils occurring over limed and reclaimed acid
heath soils; and (iv) sandy acid soils containing low native Mn.
Manganese deﬁciency has been reported for plants grown in coarse-textured and
poorly drained coastal plains soils of the United States (Reuter et al., 1988) and in
soils of Central America, Bolivia, and Brazil (Leon et al., 1985). In Europe, Mn
deﬁciency has been reported for plants grown in peaty (England and Denmark),
FAGERIA et al.
coarse-textured (Sweden and Denmark), coarse/ﬁne-textured (Netherlands), and
podzolic and brown forest (Scotland) soils (Welch et al., 1991). Manganese deﬁciency has also been reported on plants grown in semiarid regions of China, India,
southeast and western Australia, Congo, Ivory Coast, Nigeria, and other western
African countries. Manganese toxicity on crop plants grown in many parts of the
world has been reported to be more important than Mn deﬁciency (Foy, 1984;
Welch et al., 1991).
Molybdenum is the least abundant of the micronutrients in the lithosphere
(Mortvedt, 2000), and soil concentrations range from about 0.2 to 5 mg kg−1
(mean of 2 mg kg−1). Plants exhibiting Mo deﬁciency usually occur on plants
grown in broad areas of acid well-drained soils and in soils formed from parent
materials low in Mo. In Australia, Mo deﬁciency occurred on crops grown in soils
derived from sedimentary rocks, basalts, and granites (Anderson, 1970). Peaty,
alkaline, and poorly drained soils commonly have high Mo. Iron oxides adsorb
more Mo than Al oxides (Jones, 1957), and Mo adsorption on clays followed the
sequence of montmorillonite > illite > kaolinite (Goldberg, Forster et al., 1996).
Hydrous ferric oxides or ferric oxide molybdate complexes and insoluble ferric
molybdates may form in well-aerated soils so that Mo solubility and availability to
plants are low (Welch et al., 1991). In poorly drained soils, formation of soluble ferrous molybdates or molybdites may lead to high Mo availability to plants. Plants
grown in high Mo soils of the intermountain valleys of western United States
have been reported to accumulate high Mo which has induced “molybdenosis”
(Cu deﬁciency) in cattle (Welch et al., 1991).
Zinc deﬁciency is a worldwide nutritional constraint for crop production. About
50% of soils used for cereal production in the world contain low levels of plantavailable Zn, which reduces not only grain yield but also nutritional grain quality
(Graham and Welch, 1996). Total Zn concentrations in soils range from about
10 to 300 mg kg−1 (mean of 50 mg kg−1)(Lindsay, 1979). Zinc-deﬁcient soils
occur in both tropical and temperate regions, but are widespread in Mediterranean
countries like Turkey (Cakmak et al., 1997), and in New South Wales, Queensland,
and western and south Australia (Donald and Prescott, 1975; Sillanpăaaă and Vlek,
1985). In China, Zn deﬁciency has been reported on plants grown in calcareous,
desert, and paddy soils along the Yangtze river (Takkar and Walker, 1993). In
Africa, Zn deﬁciency has been observed on plants grown in Alﬁsols and Ultisols
(Cottenie et al., 1981) and in low Zn soils of Niger, Guinea, Ivory Coast, Sierra
Leone, Sudan, and Zimbabwe, which has often been induced by lime additions to
increase soil pH to near 7. In Asia, Zn deﬁciency is common for plants grown in arid
and semiarid soils (Katyal and Vlek, 1985; Welch et al., 1991). Zinc deﬁciency in
the United States has occurred mostly in plants grown in sandy, well-drained acid
soils, and in soils formed from phosphate rock parent materials of the southeast.
In the Cerrado soils of Brazil (Oxisols and Ultisols), Zn deﬁciency is widespread
(Fageria, 2000b; Lopes and Cox, 1977).
MICRONUTRIENTS IN CROP PRODUCTION
Serpentine (ultramaﬁc) soils are usually high in Ni, Co, Fe, and Mg, but low in
Ca. Nickel levels in soils are usually adequate to provide plant needs. No evidence
of Ni deﬁciency for soil-grown plants has been reported (Dalton et al., 1985),
but Ni toxicity has been of concern for plants grown in soils receiving industrial
wastes (sewage sludges, by-products) (Marschner, 1995). Cobalt deﬁciency has
been reported for ruminant animals grazing forages grown in soils low in Co such
as New Zealand, south and western Australia, The Netherlands, and the United
States (Michigan and northeastern states) (Miller et al., 1991). Cobalt is adsorbed
on Mn oxides, and liming tends to reduce Co availability to plants.
III. SOIL FACTORS AFFECTING AVAILABILITY
Many soil factors such as pH, SOM, temperature, and moisture affect the availability of micronutrients to crop plants. The effects of these factors vary considerably from one micronutrient to another as well as in their relative degree of
effectiveness. The availability of micronutrients is largely controlled by the same
soil factor(s) where good correlations exist between plant concentrations of two
or more micronutrients. The relationships associated with each of the many soil
factors are complicated, even though correlations between many factors can be
explained with relatively high certainty. A good example of this is the highly signiﬁcant negative correlation between Mo and Mn. The availability of both Mo and
Mn is so strongly affected by soil pH that the other factors are of limited value.
While Mn in plants decreases extensively with increasing soil pH, Mo increases,
and deﬁciencies of both Mn and Mo are not expected or do not usually occur in the
same soil. Manganese deﬁciency is often combined with excess Mo and vice versa
(Sillanpăaaă , 1982). Copper, Mn, and Zn were predominantly in organically bound
forms in Spodosols of Florida, whereas these elements were organically bound
and associated with Mn oxides and amorphous forms in Alﬁsols and Entisols
(Zhang et al., 1997a). Available concentrations of Co, Cu, Ni, and Zn increased
with increased amounts of clay (Lee et al., 1997).
Soil pH inﬂuences solubility, concentration in soil solution, ionic form, and mobility of micronutrients in soil, and consequently acquisition of these elements by
plants (Fageria, Baligar and Edwards, 1990; Fageria, Baligar, and Jones, 1997). As
a rule, the availability of B, Cu, Fe, Mn, and Zn usually decreases, and Mo increases
as soil pH increases. These nutrients are usually adsorbed onto sesquioxide soil
surfaces. Table IV summarizes important changes in micronutrient concentrations
FAGERIA et al.
Inﬂuence of Soil pH on Micronutrient Concentrations in Soil and Plant Uptakea
Inﬂuence on concentration/uptake
Increasing soil pH favors adsorption of B. This element generally becomes less available
to plants. Availability and uptake of B decrease dramatically at pH > 6.0.
Chloride is bound tightly by most soils in mildly acid to neutral pH soils and becomes
negligible to pH 7.0. Appreciable amounts can be adsorbed with increasing soil acidity,
particularly by Oxisols and Ultisols, which are dominated by kaolinitic clay. Increasing
soil pH generally increases Cl uptake by plants.
Solubility of Cu2+ is very soil pH dependent and decreases 100-fold for each unit
increase in pH. Plant uptake also decreases.
Ferric (Fe3+) and ferrous (Fe2+) activities in soil solution decrease 1000-fold and
100-fold, respectively, for each unit increase in soil pH. In most oxidized soils, uptake
of Fe by crop plants decreases with increasing soil pH.
The principal ionic Mn species in soil solution is Mn2+, and concentrations decrease
100-fold for each unit increase in soil pH. In extremely acid soils, Mn2+ solubility can
be sufﬁciently high to induce toxicity problems in sensitive crop species.
Above soil pH 4.2, MoO42− is dominant. Concentration of this species increases with
increasing soil pH and plant uptake also increases. Water-soluble Mo increases sixfold
as pH increases from 4.7 to 7.5. Replacement of adsorbed Mo by OH− is responsible
for increases in water-soluble Mo as soil pH increases.
Zinc solubility is highly soil pH dependent and decreases 100-fold for each unit increase
in pH, and uptake by plants decreases as a consequence.
Ni2+ is relatively stable over wide ranges of soil pH and redox conditions. However,
availability is usually higher in acidic than in alkaline soils. At pH 7 and higher,
retention and precipitation increase. Increasing the pH of serpentine soils through
liming from 4 to 7 reduced Ni in plant tissue.
Solubility and availability of Co decrease with extreme soil pH. Presence of CaCO3, and
high Fe, Mn, SOM, and moisture.
Adriano (1986), Fageria, Baligar, and Jones (1997), and Tisdale et al. (1985).
as inﬂuenced by soil pH and consequent acquisition by plants. Table V has been
provided to show acquisition of Cu, Fe, Mn, and Zn by rice grown at various soil
Boron is the only micronutrient to exist in solution as a nonionized molecule
over soil pH ranges suitable for the growth of most plants. Increasing soil pH decreases B availability by increasing B adsorption onto clay and Al and Fe hydroxyl
surfaces, especially at high soil pH (Keren and Bingham, 1985). The highest availability of B was at pH 5.5–7.5, and the availability decreased below or above this
pH range. In other studies, B adsorption increased from pH 3 to 8 on kaolinite,