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Chapter 11
Plant P nutrition and P fertilizers
Phosphorus in plant physiology
P content of plants
•
•
Approximately 0.2% of plant dry weight is P
Plants require a relatively large amount of P.
The phosphate concentration in the cytosol is
maintained at fairly constant concentrations
in the 5 to 8 mol/m3 regardless of the
external phosphate concentration except
under severe P deficiency. By contrast is the
vacuolar phosphate concentration.
Forms of P taken up
• Most P is taken up by roots as inorganic
orthophosphate ions (H2PO4- and HPO42- )
• Roots may absorb some organic P, but
the amount is very small.
• The polyphosphate(聚磷酸) was only
taken up by young barley plants after
hydrolysis to the orthophosphate(正磷酸)
form.
P uptake by plant
H2PO4- concentration in the root and
xylem sap is 100-1000 times greater than in the
soil solution
Active uptake is used to overcome this
concentration gradient.
•
•
It is likely that inorganic P is co-transported
across the plasma membrane with positively
charged ions (H+)
The transport across the membrane requires
energy. Wet or cold soils that reduce plant
metabolic activity are likely to reduce P uptake.
P uptake by plant
There are two types of transporters with
different affinities for Pi, one with a high
affinity with a Km of 3-5 mmol/m3 and the
other a low affinity system with a Km of 50 to
330 mmol/m3
Molecular studies have confirmed the
presence of multiple genes encoding
phosphate transporters that are differentially
expressed.
P uptake by plant
• Some are strongly upregulated when
phosphate supply is inadequate. Other
phosphate systems are constitutive which
are not affected by changes in phosphate
concentration in the nutrient medium.
• The pH in the apoplast controls the H2PO4the uptake rate.
Role of mycorrhizae in P uptake
1. Many plants have
associations have a symbiotic
relationship with mycorrhizae
The plants supply mycorrhizae
with C and the mycorrhizae
supply the plant with nutrients.
2. Mycorrhizae may increase P
uptake by 3-5 times.
Transport of phosphorus in plant
– P adsorbed from the roots is transported in
the xylem to young leaves. The xylem
contains mostly inorganic P.
– P can also be transported from older leaves
to younger leaves – and from the shoots to
the roots – in the phloem. The process is
known as re-translocation.
– The phloem can contain both organic and
inorganic P.
– So the P is remobilization in plant.
Regulation of P uptake
• The concentration of phosphate cycled in
phloem from shoot to root acts as a feedback
signal to regulate P uptake (Drew and Saker
1984).
• High concentrations of phosphate in the phloem
induced by low demand in shoot repress uptake.
Conversely low concentration associated with
high shoot demand stimulate uptake.
Phosphate fraction and metabolic functions
• Inorganic form:
• Most is orthophosphate, and a miner extent as
pyrophosphate(焦磷酸盐).
• Organic form:
• The organic forms of phosphate are compounds
in which the orthophosphate is esterified with
hydroxyl groups and alcohols or bound by a
pyrophosphate bond to another bond to another
phosphate group.
Phosphate fraction and metabolic functions
• Organic form:
–
–
–
–
ATP – energy storage molecule
Fructose-6-phosphate
Nucleic acids – DNA and RNA
Phosoplipids – important component of
the cell membrane, such as lecithin(卵磷
脂）
Phytin 植素– storage form for P in seeds. During seed
germination, phytin P is converted into other phosphate
forms that are needed for the young plants.
Effect of P supply on the concentration of various
P forms in spinach leaves and oat grains
(Micheal 1939)
P supply
Phospholipid
Nucleic acid
Phytate
Inorganic
P in mg/g dry matter
Oat grain
Inadequate
Adequate
0.22
2.1
0.05
0.5
0.22
2.4
0.5
1.3
-
2.2
18.0
Spinach
Inadequate
Adequate
1.1
1.1
0.9
0.9
Functions of phosphorus
• 1. The unique function of phosphate in metabolism
is its formation of pyrophosphate bonds which
allow energy transfer.
•
ATP is required for the synthesis of glucans (葡聚糖),
which supply glucosyl(葡糖基） for starch and fat.
•
UTP is required for the synthesis of sucrose, cellulose and
callose (胼胝质）with UPP-glucose as glucosyl donor.
•
CTP is needed for the synthesis of phospholipids.
• All these nucleotide triphosphates are essential blocks for the
synthesis of nucleic acids.
Functions of phosphorus
2. Controlling enzyme reactions and
the regulation of metabolic processes.
•
•
Phospofructo-2 kinase(2-磷酸果糖激酶) which
catalyzes the synthesis of fructose-2,6 phosphate.-.-a
signal metabolite which opens the glycolytic pathway(糖
酵解途径) to initiate carbohydrate degradation.
•
a new class of ribozymes(核苷酶) are made up
entirely from RNA
Functions of phosphorus
3. Photosynthesis and photosynthate
translocation.—C metabolism
•
Low concentrations of inorganic phosphate in
the cytosol prevent the export of triosephosphate
(磷酸丙糖) which leads to starch synthesis and
accumulation in the chloroplast.
•
P deficiency also decrease ATP supply and the
rates of synthesis of RuBP needed for
carboxylation(羧化作用).
Functions of phosphorus
• 4. Increase the N uptake and metabolic
• NO3-N uptake
• NO3-N reduction
• NH3 assimilation, such as amino acids
and protein
Functions of phosphorus
• 5. Improve the stress tolerance
• The drought tolerance
•
adequate P supply may counteract mild water stress
effecting tillering and leaf growth of wheat
• The cold tolerance
• The salt tolerance
ATP  1 / 2 ADP
Energy charge
EC 
ATP  ADP  AMP
(能量电荷)
The resistance to the disease
Functions of phosphorus
6. Increase crop yield and improve the
quality
P is of particularly important to fruit setting
and fruit quality
Ample P could enhance the phosphate
esterification of starch in potato tubers and thus
improves starch quality. It is true for the oil in
seed rape.
Plant Deficiency Symptoms
–
–
–
–
Stunted plants, rigid erect appearance
Delayed Maturity
Cereals tilling(分蘖) is decreased
and reduced growth rate of new shoots and
flower initiation is impaired of fruit trees
– Low yields and poor quality fruits and seeds
• Note that P is mobile in the plant. It can be
transported from older leaves to younger
leaves.
Plant Deficiency Symptoms
– In early stage of P deficiency, the leaves
become small, and dark green or bluish color
– Purple discoloration in some species
– The stem of many annual plant species are
reddish owing to enhanced formation of
anthocyanins (花青素)
Cucumber
• Plant is normal in
left
• Plant is P deficient
in right
Tomato leaves are purple as
phosphorous
Grown spots on grape leaves
Apple leaves in P deficiency
Leaves is small,
gray purple
or brown
Maize
Rape leaves
Older leaves
become redish
Wheat leave in P deficiency
The leaves and stem
is changing
from cyan(蓝绿色）
to redish or poppy（深红色）
Celery in P deficiency
Stunted,
leaves is dark, cyan(蓝绿色）,
and old leaves is yellowish
or grey die early.
Citrus fruits
Plant response to excess P
– Not directly toxic to plants or other organisms
– Extremely high P levels may reduce root growth in
some species
– Problems of excess P
•
•
May be transported into the soil by erosion or runoff from
agricultural fields.
Stimulates growth of aquatic species = eutrophication富营养
化作用
Soil Phosphorus
Total Phosphorus and forms in Soil
The total P content in the soil ranges between
0.02 - 0.15% P
The forms of P in the soil can be classified in at
least two ways:
1.Soluble-P, strongly absorbed P and mineral-P,
occluded P and organic-P
2.Soluble-P, labile-P, non-labile P
P fractions in the soil
1. Soluble P
a. H2PO4- and HPO42- (orthophosphates)
b. The amount of soluble-P in soil is very small
(<10µM), but it is very important because almost
all of the P taken up by plants is in this forms.
P fractions in the soil
2. Mineral P and strong absorbed P – many
different forms
•
Neutral and alkaline soils:
–
–
–
–
–
•
Hydroxyapatite Ca5(PO4)3OH羟基磷灰石
Fluorapatite Ca5(PO4)3F 氟磷灰石
Chloroapatite Ca5(PO4)3CI 氯磷灰石
Octophosphate Ca4H(PO4)3 磷酸八钙
Monohydrogen phosphate CaHPO4 磷酸二钙
Acid soils:
–
–
–
–
Variscite (AlH2PO4(HO)2 磷铝石
Strengite (FeH2PO4·(HO)2 粉红磷铁矿
Vivianite (Fe2(PO4)3 蓝铁矿
P absorbed strong by the Fe oxide/hydroxides, AI
hydroxides ,allophane (水铝英石） and minerals
etc
P fractions in the soil
3. Occluded phosphate (闭蓄态磷）
It is a particular form of absorbed P which is trapped and
therefore not directly available to roots.
The phosphate bridges the iron or AI with the Fe3+ or AI3+
hydroxide so that the surface of the iron or AI phosphate particle is
enveloped by an Fe3+ or AI3+ hydroxide skin.
xFePO4  3H 2O  ( x  1) FePO4  Fe(OH )3  H 3 PO4
( x  1) FePO4  Fe(OH )3  3H 2O  ( x  2) FePO4  2 Fe(OH )3  H 3 PO4
The occlude P is mainly formed in acid soil.
P fractions in the soil
• 4. Organic P
– Organic P makes up 20-80% of the total soil P
– Forms of organic P in the soil
•
•
•
•
Inositol phosphates磷酸肌醇 (10-50%)
Phospholipids (1-5%)
Nucleic acids (<1.0%)
Some unknown forms
– Like nitrogen, organic P must be mineralized
before it can be taken up by the plant.
– Nucleic acids and phospholipids are quickly
dephosphorylated by microbial phosphatase.
P fractions in the soil
1. Soluble P – P dissolved in the soil solution
2. Labile P – phosphate precipitations and held on soil
surfaces.
It is is rapid equilibrium with the P in the soil solution.
Or the organic P which is ready to mineralization.
3. Non-labile P – insoluble P, which includes primary
phosphate mineral, humus P, insoluble phosphate of Ca,
Fe and AI and P fixed by hydrous oxides and silicate
mineral
Release of P from this pool is very slow.
Schematic representation of the 3 important
phosphate soil fractions for plant nutrition
Phosphorus transformations in the soil
A.
Mineralization
B.
Immobilization
C.
Adsorption and desorption
D.
Precipitation and dissolution
E.
Weathering of primary soil minerals and release of
occluded P
Phosphorus transformations in the soil
Mineralization
– Soil organic matter contains about 1% P
– Phosphatase enzymes break down the
organic P and release orthophosphate
ions (H2PO4- and HPO42-).
•
•
The enzyme is produced by plant root and a
wide range of microorganisms.
The activity of this enzyme is high in the root
cell walls and rhizosphere, so phosphate
turnover are much higher in the rhizosphere
relative to the bulk soil.
Phosphorus transformations in the soil
Mineralization
• Factors that affect P mineralization
The same factors that affect the
mineralization of nitrogen
•
•
•
•
•
•
Temperature 30-45℃
Moisture
Aeration
pH
Microbial activity
Soil cultivation
Phosphorus transformations in the soil
Immobilization
–
–
–
Microorganisms can immobilize P by take up both H2PO4and HPO42Balance between mineralization and immobilization
The break down of organic residues low in P can induce
biological immobilization
–
–
When the C:P ratio is high (>300:1), microorganisms use available P
from the soil solution. This results in a reduction of the amount of P
available to the plants.
When the C:P ratio is low (<200:1), inorganic P is released into the
soil solution
– The importance of organic P as a source of P in
plant nutrition should not be underestimated.
Phosphorus transformations in the soil
Adsorption and desorption of P
– Adsorption – process by which ions or
molecules are taken from the soil solution
and attached to the surface of a soil solid
by chemical or physical bonds.
– Desorption – the release of ions or
molecules from the soil solid. It is the
opposite of adsorption.
Adsorption and desorption of P
•
In acid soils, the clay surfaces have Al- and
Fe-oxides and hydroxides on the surfaces of
clay minerals. The H2PO4- displaces the –
OH and –OH2+ groups and bonds to the Al
and Fe.
–
–
Labile P is bonded through one Al-O-P or Fe-O-P
bond. It can be desorbed from the surface to
replenish the soil solution.
Non-labile P is bonded through double Al-O-P or
Fe-O-P bonds. It is not easily desorbed from the
mineral surface..
Adsorption and desorption of P
• In alkaline soils, the HPO42- can absorb to
the CaCO3 through the Ca- bridge.
• Phosphate can also be adsorbed to
sesquioxide or hydrous oxide or
hydroxyoxide colloid surface through a
ligand exchange配位体交换 mechanism—
specific adsorption
Adsorption and desorption of P
• Adsorption depends not only on the type of
adsorbing minerals but also on their specific
surface. The freshly precipitated (amorphous)
material has a higher P adsorption capacity
than more crystallinic materials.
• The P adsorption declines with increasing pH
until a pH of 6-6.5
• Adsorption of P to soil particles is frequently a
combination of adsorption and precipitation.
Phosphate adsorption capacity of various adsorbents. The
adsorption index is a measure of the P absorption per unit weight
of the absorbent (Burnham and Lopez-Hermander 1982)
Absorbents
Precipitated amorphous AI(OH) 3 （水铝矿）
Adsorption
Precipitated FeOOH （针铁矿）
846
453
Fe oxyhydrate
1236
Aged Fe oxyhydrate
Laterite (红土)
111
Crystalline goethite (FeOOH)
0
Crystalline gibbsite AI(OH) 3
Calc ite (CaCO3) （方解石）
0
21
46
The relationship of charge of clay and pH
When the soil clays have positive charges,
the phosphate can be adsorbed by the electrical
attraction of ions to the charged surface.
Schematic representation of ligand exchange
absorption of P (specific adsorption专性吸附）
Precipitation and Dissolution
– Precipitation is the process in which ions
combine to form a solid that comes out of
the solution.
– Dissolution – (dissolve) process by which
the solid goes into the solution
– Acid soils
•
•
Al and Fe are the main soluble cations
These cations join with H2PO4- to form Alphosphate and Fe-phosphate which
precipitate out of the solution.
Precipitation and Dissolution
FePO4•2H2O + H2O
i.
OHH+
H2PO4- + H+ + Fe(OH)3
As acidity (H+) increases, the reaction moves to the left.
FePO4 precipitates and solution P goes down.
ii. As acidity (H+) decreases, the reaction moves to the
right. FePO4 dissolves and solution P goes up.
iii. When plant roots take up H2PO4-, the reaction also
moves to the right. FePO4 dissolves to restore P to the
soil solution.
Precipitation and Dissolution
Fe(OH ) 3  Ca ( H 2 PO4 ) 2  H 2O  2 FePO4  Ca (OH ) 2  5H 2O
FePO4  xH 2O  FePO4  xH 2O
2 FePO4  3H 2O  Fe(OH )3  H 2 PO4  H 3 PO4
FePO4  2 H 2O  Fe(OH ) 2  H 2 PO4 (粉红磷铁矿）
Strengite
如果是AI 3 在形成磷铝石（
AI (OH ) 2  H 2 PO4） Variscite
则
Precipitation and Dissolution
Neutral to alkaline soils
a. Ca is the main soluble cation
b. CaHPO4•2H2O + H+
i.
Ca2+ + H2PO4- + 2H2O
As acidity (H+) decreases, the reaction moves to the left.
Ca-phosphate precipitates and solution P decreases
ii. If acidity (H+) increases, the reaction moves to the right.
Ca-phosphate dissolves and solution P increases.
iii. When plant roots take up H2PO4-, the reaction also
moves to the right. Ca-phosphate dissolves and solution
P increases.
Precipitation and Dissolution
The apatite is formed when the Ca2+ concentration
in the soil solution is high
Ca2
Ca ( H 2 PO4 ) 2  H 2O  2CaHPO4  2 H 2O  CaHPO4
2Ca2
6CaHPO4  Ca8 H 2 ( PO4 ) 6  5H 2O
2Ca2
Ca8 H 2 ( PO4 ) 6  5H 2O  Ca10 ( PO4 ) 6 (OH ) 2
The release of occlude P
Weathering of primary soil minerals – the
release of inorganic phosphorus from
rocks due to chemical or physical factors.
Occlude P is released owing to break
down Fe3+ oxide skin of occlude P under
anaerobic conditions. In the conditions
Fe3+ is reduced to soluble Fe2+and vice
versa.
Soil P availability and soil pH
P cycle in the soil
Mineral fertilizer
Animal manures
and biosolids
Plant residue
Plant uptake
Organic P
Runoff and
erosion
Primary minerals
Microbial P
Plant residue
Humus
Plant uptake
Soil solution P
Occlude P
H2PO4HPO42-
leaching
Mineral and
humus surfaces
(clays, Fe, Al
oxides)
Secondary
compounds
(CaP, FeP, MnP,
AlP
Phosphorus remove from soil
Crop Removal
P
Leaching
(very little)
Runoff & Erosion
Phosphorus fertilizer
–
–
–
Rock phosphate (apatite) is the starting
material for most of the P fertilizers that
are produced today.
Rock phosphate contains about 6-35% P
when it is removed from the earth.
Rock phosphate is very insoluble. In its
raw form, it can only be used on some
very acidic soils.
Rocks phosphate in Morocco
Kinds of P fertilizers
• Water soluble P fertilizers
• The most of phosphate is soluble in the water
• Citric acid soluble P fertilizers
• The most of phosphate is soluble in the 2% citric
acid solution or neutral or alkali ammonium
citrate
• Citrate-Insoluble P fertilizers
• Most of phosphate is insoluble in the water and
citric acid
• Available P = water-soluble P + citrate soluble P
Straight phosphate fertilizers
Name
Chemical composition
Solubility
Concentration of P2P5 in %
Superphosphate
Ca(PO
Ca(H
4)42)+CaSO
4 4
2PO
2+CaSO
Water sol.
18-22
Ca(H
Ca(PO
4)2 4)2
2PO
Water sol.
46-47
Monoammonium phosphate
NH4H2PO4
Water sol.
50-52
diammonium phosphate
(NH4)2HPO4
Water sol.
46-48
Basi slag (Thomas slag)
Ca3P2O8·CaO+CaO·SiO2
Citric acid sol.
10-22
CaNaPO
CaNaPO4
Ca2SIO4
4 CaSiO
4
NH4 citrate sol.
25-29
Fused Mg phosphate
Α-Ca
CaSiO3 3
αCa
)28+CaSiO
3P 24O
3(PO
Citric acid sol.
20
Ground rock phosphate
Apatite
insoluble
29
Triple superphosphate
Sinterphosphate (Rhenania)
Common P fertilizers（普通过磷酸钙）
Ordinary or single superphosphate (SSP)
2 Ca5(PO4)3F(pulverized) + 7 H2SO4
CaSO4 + 2 HF
3 Ca(H2PO4)2 + 7
•
Properties:
•
Grey, ground 粉末or granule 颗粒
•
0-20-0
•
85% water soluble
•
Acids
•
It contains S which was an advantage in the past.
Table ingredients of SSP (super grade)
Ingredient
content（%）
Ingredient
content（%）
Water
＜3.5
Mn
0.02
Total P2O5
20.6
Cr
0.005
Soluble P2O5
20.3
K
0.06
Free acid
3.2
CI
0.005
F
1.6
Ti
0.04
AI2O3
1.3
Cu
0.004
Fe2O3
0.7
Na
0.2
SO4
27.4
I
0.001
CaO
29.4
V
0.007
SiO2
3.0
Mg
0.2
Water solubleP2O5
19.7
N
0.05
Phosphate degradation (磷肥退化作用)
The water soluble P in the superphosphate turn out to insoluble
P such as FePO4 or AIPO4 owing to free acids
and higher moisture in the fertilizer.
Fe2(SO
 H 22O
Fe
·2H
O
2(SO4)4)33
AI2(SO
 2H O
AI2(SO4)2
4)3·2H22O
 Ca( H 2 PO4 ) 2  H 2O  5H 2O 
2FePO4
 CaSO4  2H 2O  2H 2SO 4
2AIPO 4
Reactions of fertilizer P in the soil
–
–
–
–
Most phosphorus fertilizers have high water solubility.
When they are applied to the soil, the fertilizer dissolves,
releasing soluble phosphates into the soil solution and
increase H+ nearby, which increase the Ca, Fe and AI
solubility.
The phosphates react quickly with the cations in the
solution to form insoluble compounds. Some of the
phosphorus may be adsorbed onto the oxide surfaces.
Within a few days, much of the soluble P is converted into
insoluble compounds into the soil. With time these may be
converted into forms that are even more insoluble.
The process is called the abnormal solubility of
superphosphate (过磷酸钙的异成分溶解作用)
Reactions of fertilizer P in the soil
Soluble Iron and AI
Insoluble phosphate
Direction of water
Direction of P solution
Changes of superphosphate in soil
Application of SSP
• It is suitable for most soil types and all crops,
especially neutral or alkaline
• It is suitable for basal fertilizer, pop-up or starter
and top dress
• In soil with higher capacity of fixation, it should be
applied in granule form or as bands within the soil
in close proximity to the roots
Triple superphosphate (TSP)
2 Ca5(PO4)3F + 12 H3PO4 + 9 H2O
+ 2HF
（重过磷酸钙）
9 Ca(H2PO4)2
•
O-46-O
•
85 - 87% Water soluble
•
A popular fertilizer in the past, is used less now.
•
It has the abnormal solubility
•
It is used similar to superphosphate, but the rate is
small than SSP.
Diammonium phosphate (DAP)
2NH3 + H3PO4
(NH4)2HPO4
•
Characteristics and properties
•
18-46-0
•
90-100% water soluble
•
Very common P fertilizer
•
Can be blended with other fertilizers or applied directly.
•
It has a high N content and often has an economic
advantage over other fertilizers.
•
The high ammonia content may reduce germination, if DAP
comes in direct contact with the seed.
Ammonium polyphosphates (聚磷铵）
3NH3 + H4P2O7
(NH4)3HP2O7
•10-34-0 or 11-37-0
•100% water soluble; Liquid fertilizer; Very safe material
•Chelates micronutrients (chelates = joins together with iron, Mn,
zinc etc)
Polyphosphate is composed of many orthophosphate molecules
connected together. If stored for a long time, the polyphosphate
may hydrolyze to form orthophosphates.
Some researchers claim that polyphosphates can increase
micronutrients uptake, but others disagree.
Fused Mg phosphate (钙镁磷肥）
• Fused Mg phosphate is produced by a
disintegration分解 of rock phosphate and
rocks with Mg such as olivine(橄榄
石）,dolomite（白云石）, silica（硅石） in a
rotary kiln at about 1250℃.
• Characteristics and properties
• P2O5 14%-18%
• Citric acids soluble
• Grey , ground
• Alkaline
Reaction in the soil
• In acids soil (pH<6.5)
  Ca3 ( PO4 ) 2  2CO2  2H 2O  2CaHPO4  Ca ( HCO3 ) 2
CaHPO4  2CO2  2 H 2O  CaH4 ( PO4 ) 2  Ca ( HCO3 ) 2
• In calcareous soil
When lime potential石灰位 is bigger than 4
3  Ca3 (PO4 )2  Ca(OH )2  Ca10(PO4 )6  (OH )2
Application of fused Mg phosphate
• It is suitable for acid soil
• It is suitable for the P deficient soil such
as sandy soil leanness or barren soil
贫瘠土壤
• It is suitable for basal fertilizer, not top
dress or side dress
• It is suitable for crops which need more
P such as legumes and cereal crop
Ground rock phosphate (磷矿粉）
• Characteristics and properties
• P2O5 10%-25%
• Most of phosphate is insoluble, only 1-5% is
citric acid soluble
• Hard crystalline are very insoluble and thus
almost useless as fertilizer
• Soft rock phosphates consist mainly of apatite
with only a minor proportion of Fe3+ and AI3+,
and a few of CO2. Ground soft rock may be
used as fertilizers, such as francolite细晶磷灰
石.
Reaction of ground phosphate rock in soil
• In strong acid soil

2
2
Ca5 ( PO4 )3  F  4 H  5Ca  3HPO4  HF
Ca5 ( PO4 )3  F  3Fe3  H   3FePO4  5Ca 2  HF
3

Fe  H 2 PO4  2 H 2O  2 H   Fe(OH ) 2 H 2 PO4
表4-11磷矿成因、理化性质与有效磷的关系
全磷
有效磷
CO2
占全磷
（P2O5）（P2O5）
（%）
量（%）
%
%
结晶程
磷矿成因
度
折光率
沉积变质
晶粒状
磷灰石
1.6303 3.1804
0.18
41.094
1.52
3.62
石灰砂质 胶状隐
磷灰石
晶
1.6192 3.1452
1.45
40.39
7.90
19.55
泥灰质磷
灰石
1.6079 3.1174
4.19
36.30
11.80
32.51
胶状
比重
The solubility of soft rock phosphate depends
much on the origin or provenance起源.
Application of the ground rocks
• It is only effective in the strong acid soil
and very P deficiency soils

pH2 PO4  2 pH  5.18
• It is suitable for the crops which have
higher ability to uptake P
• It should be applied in great rate.
Table the relative effect of rock phosphate
on the different kind of crops
super
significantly
effective
Significantly
effective
moderate
significantly
effective
No
significantly
effective
Rice*
Rape 80%
Vica villosa苕子
70～80%
Maize 50 ～
60%
Millet 20 ～
30%
20 ～25%
Radish 80%
Pea 70～80%
Potato,
sweet potato
50%
Wheat, rye,
oat etc.15 ～
30%
Buckwheat
80%
Soya,
Astragalus
sinicus紫云英
etc70%
Gingeli 芝麻
40%
Peanut ,
Rattlebox猪屎
豆, Sesbania
cannabina田青,
etc70%
Phosphorus Fertilizer Management
• The P efficiency or recovery of P
• Less than 15%-20% of the fertilizer applied to
the soil, is usually recovered by a crop grown
immediately after application.
• The main reason of the low recovery is the
fixation of P.
• The accumulation recovery of P fertilizers
are high.
Phosphorus Fertilizer Management
• The principles of effective application of P
fertilizer:
• 1. According to Properties of fertilizers
• 2. According to the properties of soils and
history of P application
• 3.According to the capability of plant
uptake
Phosphorus Fertilizer Management
4. P interact with other fertilizers such as N,
K, organic manure and micronutrients etc.
5. The appropriate rate of P application is
important.
The rate generally applied to arable crops
from 20-80kg p/ha according to crops species
and available soil phosphate. On soils with a
high P adsorption capacity, however rates of 100
to 200 kg/ha may be applied.
Phosphorus Fertilizer Management
6. Application methods
–
–
P is very immobile in the soil (movement is
primarily by diffusion). Fertilizer must be placed
where it can easily be taken up by plants roots.
Minimize fixation.
Because P is easily fixed by the soil, try to
minimize the contact between P and the soil.
This can be done by placing the P fertilizer in
bands.
Granule of pellet fertilizers.
Phosphorus Fertilizer Management
•
Surface application – P has limited mobility
in the soil. Surface applied P will move to
the roots very slowly.
•
–
Surface application is is acceptable in permanent
grass or forage fields. These crops have a lot of roots
near to the surface.
Broadcast and incorporation
•
–
Places P in the root zone, but increases the P to soil
contact. This increases the P fixation potential.
Band placement
•
Placing P in bands minimizes the contact between
soil and fertilizer. Reduces fixation potential.
Phosphorus Fertilizer Management
•
Best application method
–
Depends on the quantity of P in the soil
and the soil type.
•
•
Banding is the best method on soils with low
P and high P fixation capacity.
If soils are already high in P or if they have a
low fixation capacity, then broadcast
applications are acceptable.