B deficiency of cucumber. older leave developed yellow
B deficiency of cucumber. older leave developed yellow
Boron & molybdenum
Total boron in the soil
The content of B in the soil
ranges between 20-200 mg/kg dry
weight. Most of which is inaccessible
Boron in the soil solution
1. Between pH 5 and 9, H3BO3 is the
dominant form of B in the soil
2. The pH of the soil solution and the
amount of clay, oxides, and organic
matter are important factors that
affect B availability.
B containing Minerals
Tourmaline (30-40 mg B/kg) and
AI and Fe oxides, clay minerals, calcium
carbonate, and organic matter
Organic matter bound B
the sorption capacity for B in composed
organic matter is about 4 times greater
than for soil or clay. It is believed to be
thru ligand exchange.
Hot water soluble B (0.5-2.0 mg B/L)
Soluble B consists mainly of boric acid
which under most soil pH conditions (pH
B(OH)3 + H2O
Factors affecting boron availability
Absorption of B is closely dependent on soil
pH, adsorption increase the pH range 5-9
2. B leaching
In acid, sandy soil or podzolic soil, B is easily
leached from soil; but in arid and semiarid regions,
B may accumulate to toxic concentration.
3. Organic matter
Native B and hot water soluble B in soil are
significantly correlated with organic C content.
Percentage of sugar beet
Soils developed from sandstones and acid
Spodosol and podzols
Sometimes Andosols, Lithosols and Luvisols
Liming acids with marginal B concentrations
Hot water soluble B <0.5 mg/L
Boron in plant
B uptake is a possible combination of
active transport as esters with cis diols and
passive diffusion as undissociated boric acid.
But the exact nature of boric acid
transport across cell membrane is still not
To most of plant species, B is
translocated through the xylems, and limited
phloem. It is controlled by the transpiration
B is not readily transported in the plant.
Deficiencies occur first in the growing points
and young leaves.
But in some species, such as celery,
carrot, bean, and cauliflowers, apple, pear,
and aprico, B is mobile and is transported as
a complex with polyols .
B is now believed to play a key role in the
structure and integrity of cell walls. The
chemical composition and ultrastructure of
cell walls are quickly affected by a lack of B.
The role of B in cell walls is cross linking
of pectic polymers (B-RG）.
It is important to cell wall structure.
1.The effects of B are thus mediated either
directly or indirectly by the plasmamembrane
bound H+ pumping ATPase.
2.The effects of B are primarily on
plasmmembrane itself (Cakmak and RÖmheld
B stabilizes the structure of plasma membrane by
complexing membrane compounds containing cisdiol groups such as glycoproteins and glycolipids to
keep channels and enzymes at optimum conforation
within the membrane.
3.B exerts its most important influence at the
Function of B in the plant
B was associated with the higher growth
rate of pollen tubes.
IAA levels is regulated by the B via IAA
• Meristematic activity
synthesis of N-bases such as uracil
Abnormal or retarded growth of apical
growing points, in advantage stage, death
of the terminal growing points
2. Stems have an unusual shape. They may
become thick and crack.
3. Youngest leaves are misshapen, wrinkled
and are often thicker and of a darkish bluegreen color. Irregular chlorosis between
the intercostal veins occur.
4. The roots may grow in a very unusual way.
In turnips and swedes, B deficiency result in glassy like
root which are hollow and cracked
5. Flower and fruit formation is restricted or inhibited.
The tissue of the fruit may have some soft, brown spots.
Sometimes it results parthenogenesis.
Drop of buds, flowers and fruits
Fruits developed remain very small and are of poor quality.
Growth stunted; growing point killed;
leaves dull grayish green, changing to yellow before dying off.
Boron toxicity shown by narrow brown
rims on leaflets;
magnesium deficiency by intervenal
necrosis and withering
B deficiency of cucumber. older leave developed yellow；
new leave are distorted and appear mottled；Aborted fruit
(top); twisting and scarring；
B deficiency: Stems stiff; terminal buds die and
growths die back （up is capsicum；bottom is
cucumber and tomato）
• Fruits pitted and
corky areas in skin;
Cauliflower Head Boron deficiency
Browning of curd
Longitudinal section. Browning of curd and
lesions in•pith. (Not specific for boron; may be
due to other causes in the field) Secondary
infection of Bacillus Carotovorus.
Corky condition of epidermis (bottom)
Young Sugar Beet Plant Boron deficiency
• Early stage of boron deficiency. Young leaves distorted
and fail to expand.（left)
“Crown Rot“ and death and distortion of young leaves;
older leaves cracking and distortion of laminae, yellow
pigment formation and severe marginal scorch. (right)
Table Beet Plants Boron deficiency
• Collapse of foliage, beginning with young leaves;
rotting of outer tissues of the roots. ("Canker") ；
Transverse section. "Canker" lesions, mainly
in outer tissues.
Rough skin condition which may accompany
"Brown Heart" condition.
• Swede Plant Boron deficiency
• Mottling and tinting of foliage and death of
growing point. (right)
• Rough skin condition which may accompany
"Brown Heart" condition. (middle and right)
Runner Bean Stem and
Leaves Boron deficiency
• Stem thickened and stiff;
growing points die; leaves
slight chlorotic mottling.
Growth of young leaves restricted giving a
older leaves orange tints; growing point
Crops differ in their sensitivity to B deficiency.
Most sensitive crops: Cruciferae such as cabbage,
turnips, brussels, sprouts, cauliflower and
Chenopodiaceae such as sugar beet and swede.
Others crops sensitive to B deficiency: celery,
groundnut, coffee, oil palm, cotton, sunflower, olive,
Legumes and fruit trees have a high B requirement
Graminaceous monocots have a low B requirement.
The symptoms of B toxic often occurs on
the older leaves.
Begins with chlorosis on the tips and
margins and finally spreads between the
lateral vein, followed by progressive
necrosis in the advanced stage.
The leaves take on a scorch appearance
and drop prematurely.
B toxicity of Mellon（left of up）
and sweet potato (bottom0
+B Symptoms of B
toxicity are first
seen in older leaves.
by necrosis. Note
necrotic spots ,and
large areas of dead
Arid and semi-arid soils with high B level
B concentration in the irrigation water
>0.3-1mg/L for sensitive crops; 1-2mg/L
for semi tolerant plants and 2.1-4 mg/L
for tolerant plants
Sensitive crops: peach, grapes, kidney
beans and figs
Semi-tolerant crops: barley, peas, maize,
potato, lucerne, tobacco, and tomato
Most tolerant crops: turnips, sugarbeet
boric acid (H3BO3
boron frits (Na2B4.XH2O)
Sodium tetraborate (Na2B4O7.5H2O)
sodium pentaborate (Na2B10O16.10H2O)
solubor (Na2B4O7.10H2O + Na2B10O16.10H2O)
***Most compound fertilizers in Zim supply trace
amounts of boron
Application of boron fertilizer
1. Soil application
early autumn or anthering
3. Application as starter or pop-up
Content of Mo in soil
0.8-3.3 mg/kg in agriculture soil
Soil derived from granitic rocks , shells,
slates or argillaceous schist are often
high in Mo
Highly weathered acids soils tends to be
Soils formed from igneous rocks and
shale and poorly drained neutral or
alkaline organic soils have high level Mo
Fraction of soil Mo
Mo occluded with oxides
Mo solids phases： including molybdenit
(MoS2), powellite (CaMoO4), ferrimolybdite
(Fe2(MoO4)3 and PbMoO4.
Mo associated with organic compounds.
Mo availability in soil
Molybdate is the most prominent form in
soil solution above a pH about 4.
Molybdate is absorbed by sequioxides and
clay minerals via ligand exchange similar to
The Mo concentration in soil solution is
usually determined predominantly by soil
pH and total Mo content of the soil.
As the pH falls the Mo soil solution
Soils derived from quartzic material, sandy
pebbly alluviums, and sandy loam and soils
with high anion exchange capacity are often
Calcareous soil derived from loess and
Content of Mo in plant
The Mo concentration of plant materials is
usually low and plants are adequately
supplied with less than 1 mg/kg dry
matter. Deficiency is usually under 0.2
mg/kg dry matter.
Sugar beet tops
Phaseolus bean tops
Tomato leaves, healthy
Tomato leaves, deficiency
Mo uptake and translocation
Mo is absorbed by plants as molybdate.
The uptake is depressed by the SO4- and
Mo may possibly move in xylem as
MoO42-, as Mo-S amino acid complex or
as a molybdate complex with sugar or
Mo is moderately mobile in plant.
Mo is an essential component of nitrate
reductase and nitrogenase
Mo plays another essential role in the N
metabolism in legumes such as soybean
and cowpea.—xanthine dehydrogenase
Synthesis of vitamins
IAA oxidase activity
Chlorophyll structure stability
Mo deficiency frequently begins in the
middle and older leaves.
Interveinal mottling, marginal chlorosis of
the older leaves and upward curling of the
leaf margins are all typical.
As the deficiency progress necrotic spots
appear at leaf tips and margins.
In the cruciferae the lamella is not properly formed and
in the extreme case only the leaf rib is present, like a
whip, so the deficiency is called “whiptail”
Curd formation is also distorted
In Mo deficiency maize the tasseling stage is delayed;
flower fail to open and grain size and viability is
greatly reduced; premature sprouting of grains.
Mo deficiency of cauliflower: interveinal mottling, marginal chlorosis
of the older leaves and upward curling of leaf margins and tip
necrosis in early stage；in the serious deficiency, leaf lamella is
not properly formed and in extreme case only the leaf rib is present.
it is called whiptail）；curd formation is also distorted.
TOMATO PLANTS Molybdenum deficiency
Leaflets somewhat chlorotic, strongly incurled and die
back from tips.
Left: healthy leaf receiving molybdenum. Right:
Molybdenum deficient leaf; leaflets, incurled margins,
intervenal chlorotic motting and death of tips.
• Leaves cupped and
around margins; tips
and margins develop
dead patches; plants
fail to heart. (Similar
to manganese toxicity；
High Mo levels in fodder and a Mo
concentration of 5 to 10 mg Mo/kg in the
dry matter is dangerous to ruminants such
Molybdenosis : diarrhoea, depigmentation )
of hair or wool, bone formation and
reduction in growth.
Poorly drained soils derived from granitic
alluvium and black shales ash on highly
Molybdenum trioxide MoO3 Mo 60%
Na molybdate Na2MoO4.2H2O Mo 38-46%