Soil Fertility Management 5 Phosphorus
International Program in Agricultural Development Studies (IPADS)
ZEF‐IPADS Joint Lecture (18‐22 Jan. 2016)
20 January 2016
Topics
IPADS Soil Fertility Management ‐6‐
Phosphorus
1. P cycle
2. Forms and functions of P in plants
3. Forms of soil P
3‐1. Solution P
3‐2. Mineral solubility
3‐3. Adsorption reactions
3‐4. Factors influencing P fixation in soils
3‐5. Organic soil P
4. P sources
5. Management
Department of Global Agricultural Sciences
IPADS
Kensuke OKADA
([email protected]‐tokyo.ac.jp)
ipads.jp/soil
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(Llanos Orientales in Colombia, photo by KO)
Phosphorus cycle
1. P CYCLE
http://www.sumanasinc.com/webcontent/animations/content/p
hosphorouscycle.html
(SOURCE: Cain, et al., Discover Biology, Third Edition, W. W. Norton & Co.
© 2006 W. W. Norton & Co.)
P amount of P pools and their flows in agricultural soil P cycle in soil
（Randall et al 2001 after Richardson 1994)
SOIL
ORGANIC
MATTER
(Nonlabile P)
Labile P)
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Soil Fertility Management 5 Phosphorus
ZEF‐IPADS Joint Lecture (18‐22 Jan. 2016)
Forms and Functions of P in plants
2. FORMS AND FUNCTIONS OF P IN PLANTS
Important!
Visual Deficiency Symptoms
• Overall stunting
• Darker green color
• Purple leaf color (corn and grasses)
• Less tillering (rice)
• Mobile in plants (lower leaves symptoms)
• Delayed flowering and maturity
• P ‐‐‐ 0.1‐0.5%
• Absorption : H2PO4‐ or HPO42‐
Forms in plants
• Energy storage and transfer (ATP/ADP)
• DNA, RNA
• cell membrane
Phosphorus deficiency symptoms
NPK trial of sorghum on an Alfisol fields
NPK N K P
4‐Sep‐1986 ICRISAT, Panancheru, India Sorghum in NK plot on Alfisols (RP16: A1) at ICRISAT
S o r g h u m
P i g e n o n e a 2
Soil Fertility Management 5 Phosphorus
ZEF‐IPADS Joint Lecture (18‐22 Jan. 2016)
Sorghum in NK plot on Alfisols (RP16: A1) at ICRISAT
Top total dry weight (g/m2)
S o r g h u m
P i g e n o n e a 3‐1 Solution P
3. FORMS OF SOIL P
Soil solution P concentration to support crop growth
Influence of pH on the distribution of orthophosphate species in solutions
Influence of inorganic P in soil solution on corn grain yield
Mass flow vs. diffusion
• Case of Mass flow : Transpiration ratio (H2O (g)/dry matter (g)) = 400
Tissue concentration of P = 0.2% in crop, average P conc. in soil solution is 0.05 ppm P
? How much does mass‐flow P contribute?
• Diffusion
P diffusion is the primary mechanism of P transport especially in low‐P soils
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Soil Fertility Management 5 Phosphorus
ZEF‐IPADS Joint Lecture (18‐22 Jan. 2016)
P fixation / P retention
1. Adsorption (吸着） to mineral surface
2. Precipitation(沈殿） as secondary P compounds
Factors
1. pH (next figure)
2. P concentration
adsorption ‐‐‐ low conc.
precipitation – high conc.
pH is the important factor for the type of P fixation
3‐2 P MINERAL SOLUBILITY
Common P minerals found in acid, neutral, and calcareous soils
Important!
Soil solution P concentration is ultimately controlled by P mineral solubility. e.g.
Solubility of Ca, Al and Fe phosphate minerals in soils
Please note:
1. effect of pH on Al‐P, Fe‐P
2. pH 6‐6.5
3. effect of pH on Ca‐P
4. CaCO3 precipitates at >pH7.8
5. P minerals that support the lowest P conc. are the most stable
6. When fertilizer is added .....
3‐3 P ADSORPTION REACTIONS
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Soil Fertility Management 5 Phosphorus
Adsorption mechanisms
Acidic soils
ZEF‐IPADS Joint Lecture (18‐22 Jan. 2016)
Adsorption equation
Freundlich
Langmuir
Calcareous soils
1. low‐P ‐‐‐‐‐ small quantities adsorb CaCO3 surface
2. high‐P ‐‐‐‐‐ Ca‐P minerals precipitate on the CaCO3 surface
Factor : Soil minerals
• Andepts
‐reactive amorphous Al oxides
• Oxisols
‐Fe/Al oxides
‐amorphous Al hydroxy
compounds
3‐4. FACTORS INFLUENCING P FIXATION IN SOILS
• Calcareous
‐ CaCO3 surface
Other factors affecting adsorption
• Soil pH : P availability if highest at 6.5
• Cation effects : Exchangeable Al3+ precipitate P
• Anion effects : Inorganic and organic anions compete P adsorption site and decrease adsorption
• P saturation • Soil OM : anions compete P (citrate, oxalate, tartarte
and malate)
• Time and temperature
• Flooding
• Fertilizer P management considerations
broadcast and incorporation vs. band placement
3‐5. ORGANIC SOIL P
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Soil Fertility Management 5 Phosphorus
ZEF‐IPADS Joint Lecture (18‐22 Jan. 2016)
Proportion of organic P in total P
Organic P in the soils
• Phytic acid (myoinositol hexaphosphate) 10‐50%
• Phospholipids (1‐5%)
• Nucleic acids (0.2‐2.5%)
About 50 %, ranging 15 to 80%. Indices to show P content/availability of fertilizers
• water soluble
• citrate soluble
1N ammonium citrate soluble
• citrate insoluble
• available
water soluble + citrate soluble
• total P
4. P SOURCES
Rock phosphate Egyptian rock phosphate
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•
•
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CO3‐F apatite
0 in water soluble, but 5‐17% citrate soluble
Available low pH soils (2‐3 times )
Extensive plantation (e.g. rubber, oil palm, cacao on very acid soils)
• Warm climate, moist soils, long growing seasons
• High initial dose (10‐30 t/ha) and 5‐10 years repetition
Common phosphorus fertilizers
Single Super Phosphate (SSP)
Triple Super Phosphate (TSP) (Source: IPNI)
Diammonium
Phosphate (DAP)
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Soil Fertility Management 5 Phosphorus
ZEF‐IPADS Joint Lecture (18‐22 Jan. 2016)
5. MANAGEMENT
Low mobility of P in the soil
Residual effect of P fertilizer
Residual effect and P management
Effect of band‐
application on soil P
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Soil Fertility Management 5 Phosphorus
ZEF‐IPADS Joint Lecture (18‐22 Jan. 2016)
Phosphorus ‐ Summary
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•
•
•
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Low P concentration in soil solution
P‐fixation (adsorption and precipitation)
pH and forms of inorganic P
Forms of organic P
Initial intensive application, repeat after certain years
• Broad application and band application
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