PERANAN HARA DALAM TANAMAN - Spada UNS

FOSFOR.

Jumlah dalam Tanaman: 1/5 sampai 1/10 lebih rendah dari N berat kering , sama dengan Ca, Mg dan S unsur makro dalam tanah

Tanaman menyerap P dalam bentuk : H₂PO4^-1 atau HPO4^-2 tergantung pH

TRANSFORMASI DALAM TANAMAN :

Tidak ada perubahan yang besar dari Ortofosfat yang diserap tanaman

Mobilitas dalam tanaman :

Fosfor dapat dipindahkan ke seluruh tanaman baik melalui Xylem maupun floem

Jika terjadi kekurangan P dalam tanaman, maka P dari daun tua akan dipindahkan ke jaringan muda.

FOSFOR

Phosphorus in Soils

• Soils may contain from 0.1 to 0.02% P

• N:P ratio in soils is about 8:1

• There is little relationship between total soil P and

available P; only a tiny fraction of total P is available to plants

• Forms of soil P:

• Organic - various P forms associated with humus

• Inorganic - mineral P, adsorbed P

• P in soil solution (ionic forms)

Phosphorus behavior in soils

 PO₄^3- will react with:

 whatever cation is in greatest abundance and,

 whatever cation is held with the strongest bond.

 In nature, there is plenty of water around:

H₂O === H⁺ + OH^-

Concentration of H⁺ = OH^-

= 10

^-7

 PO₄^3- will react with:

 whatever cation is in greatest abundance and,

 whatever cation is held with the strongest bond.

 In nature, there is plenty of water around:

H₂O === H⁺ + OH^-

Concentration of H⁺ = OH^-

= 10

^-7

Phosphorus behavior in soils

 When the charges on phosphate are all satisfied by H⁺, in the laboratory, the

compound phosphoric acid is formed.



H

₃

PO

₄

 When the charges on phosphate are all satisfied by H⁺, in the laboratory, the

compound phosphoric acid is formed.



H

₃

PO

₄



Review



Review

HO - P - OH HO - P - OH

O ll O ll

l

OH

l

OH

Phosphorus behavior in soils

 The H⁺ leave (dissociate from) phosphoric acid in a stepwise manner when the acid is reacted with base, like sodium hydroxide (NaOH).



H

₃

PO

₄

 H

⁺

+ H

₂

PO

₄^-



H

₂

PO

₄^-

 H

⁺

+ HPO

₄^2-



HPO

₄^2-

 H

⁺

+ PO

₄^3-

 One or more of the phosphate forms will be present in solution, depending upon the

solution pH.

 The H⁺ leave (dissociate from) phosphoric acid in a stepwise manner when the acid is reacted with base, like sodium hydroxide (NaOH).



H

₃

PO

₄

 H

⁺

+ H

₂

PO

₄^-



H

₂

PO

₄^-

 H

⁺

+ HPO

₄^2-



HPO

₄^2-

 H

⁺

+ PO

₄^3-

 One or more of the phosphate forms will be present in solution, depending upon the

solution pH.

Phosphorus behavior in soils

 One or more of the phosphate forms will be present in solution, depending upon the

solution pH.

 One or more of the phosphate forms will be present in solution, depending upon the

solution pH.

Mole fraction of phosphate ionic species with pH.

0.00 0.20 0.40 0.60 0.80 1.00

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Solution pH

Mole fracton P

H3PO4 H2PO4 HPO4 PO4

Al³⁺ + H₃PO₄ ^== AlPO₄

DAP Al³⁺ + (NH₄)₂HPO₄ ^==  AlPO₄ + 2 NH₄⁺ MAP Al³⁺ + NH₄H₂PO₄ ^==  AlPO₄ + NH₄⁺

 AlPO₄ is very insoluble.

 The reaction rate depends on the concentrations of Al³⁺ and H₃PO₄ in the soil solution

.

27 lbs Al³⁺ will react with about 71 lbs P₂O₅ to form AlPO₄

.

Al³⁺ + H₃PO₄ ^== AlPO₄

DAP Al³⁺ + (NH₄)₂HPO₄ ^==  AlPO₄ + 2 NH₄⁺ MAP Al³⁺ + NH₄H₂PO₄ ^==  AlPO₄ + NH₄⁺

 AlPO₄ is very insoluble.

 The reaction rate depends on the concentrations of Al³⁺ and H₃PO₄ in the soil solution

.

27 lbs Al³⁺ will react with about 71 lbs P₂O₅ to form AlPO₄

.

Below soil pH 5.5 there are increasing amounts of Al³⁺ ~ H⁺

.

Mineralization-Immobilization of P

Organic P Inorganic P

Immobilization and Mineralization of soil P are similar to that of N:

If added organic materials have a C:P ratio of

>300, there will be net immobilization P if <200 there will be net mineralization of P

Mineral Forms of P

• In neutral to alkaline soils, most mineral P will be as Ca-phosphates. Most of these are quite

insoluble.

• In acid soils, most mineral P will be as Fe and Al- phosphates. Most of these are quite insoluble.

• The insolubility of most P minerals is one

important reason that P availability to plants is usually low.

Adsorbed P

• Phosphate ions (HPO₄^-, H₂PO₄^2-) are strongly adsorbed to the surfaces of:

• Iron oxides, especially in acid soils

• CaCO₃, especially in alkaline soils

• Adsorption is at a minimum in neutral (6-7) pH

• Adsorption reactions are another reason that P availability in soils is limited.

Brady and Weil, Figure 13.10

Phosphorus availability and pH

P Reactions with Soil Minerals

Phosphorus Reactions in Desert Soils

H₂PO₄^- HPO₄⁼

Ca₈H₂ (PO₄)₆ octocalcium

phosphate

Na₂HPO₄ sodium phosphate

Calcareous soils

Sodic soils Inorganic P

Nutrient Mobility in Soils

• Mobility in soils refers to the relative rate of movement of soluble nutrient forms in soils.

• Mobility is a function of soil texture and mineralogy (generally slower in clay soils)

• Usually, N (NO₃^-), S (SO₄^2-), and Cl (Cl^-) are considered mobile in soils

• Most other elements are less mobile in soils.

Nutrient Mobility in Soil

Soil volume exploited for mobile nutrients:

N, S, Cl

Soil volume exploited for immobile nutrients:

Most others

Because P is immobile, we cannot rely

on movement of irrigation water to transport P.

Apply immobile nutrients here (close to roots)

SERAPAN P

• Bentuk H

₂

PO

₄^-1,

HPO

₄^-2

P dlm tanaman tetap berada dalam bentuk oksidasi

Type serapan P

• Serapan P bersifat aktif → diatur respirasi karbohidrat

• Konsentrasi dalam xylem SAP 100- 1000 X > di luar akar → terjadi perbedaan konsentrasi

Faktor yang mempengaruhi serapan

P

• pH tanah,

• pada pH rendah << 4, Serapan 4x > pH 8.7 , karena eksudat akar ( as. Amino, as. Organik ) P lebih tersedia

• Jenis/spesies tanaman

Tan dengan rambut akar >>>

Permukaan akar >>>  daya serap P >>>

Bentuk bentuk P setelah diserap tanaman

 Tetap sebagai P anorganik (Pi) H₂PO4^-

 Teresterifikasi melalui hidroksil ke rantai karbon (C-O-P), sebagai esterfosfat sederhana, contoh : Gula Fosfat

 Terikat pada fosfat lain dengan ikatan pyrofosfat kaya E (P  P),contoh : ATP

 Terikat sebagai diester yg stabil; (C-P-C), dlm ikatan ini P membentuk jembatan penghubung antara

unit2 menjadi struktur makromolekul yang kompleks

• Laju pertukaran antara Pi ke P dlm ester fosfat dan ikatan pirofosfat sangat cepat.

• Pi yang diserap tanaman segera menjadi P organik dlm beberapa menit, setelah itu Pi dilepaskan kembali ke Xylem

Turn over times of Organic Fosfat Fraction

Fraksi P 

(nmol / g twt)

Turnover Time (minute ATP

Glucose – 6P Fosfolipid

RNA DNA

170 670 2700 4900 560

0.5 7 130 2800 2800

• Begitu masuk ke akar tanaman, P akan disimpan di root atau diangkut ke bagian atas dari tanaman.

• Melalui berbagai reaksi kimia, itu dimasukkan ke dalam senyawa organik,

• asam nukleat (DNA dan RNA),

• fosfoprotein, fosfolipid, gula fosfat, enzim,

• fosfat kaya energi senyawa ... misalnya, adenosin triphosphate (ATP).

Serapan dan Transportasi Fosfor

PERANAN P DALAM TANAMAN

1. P sebagai elemen struktural

P  Penyusun struktur makromolekul (asam Nukleat)

DNA – Pembawa informasi genetik

RNA – penterjemah informasi genetik Ribose – O – P – O – Ribose – O – P – O - Ribose

O^-

O

O^-

O

P  penyusun fosfotidilcholine / lecitin

Digliseride – P – O – amine choline

- O

O

P penyusun fosfolipid dalam biomembran Digliseride – P – O

O^-

O

Asam amino / Amin /

Alkohol

2. Transfer energi

• Ester fosfat (C-P) dan Fosfat kaya energi (P-P) merupakan

energi metabolisme dalam sel

Ada 50 ester teridentifikasi, yang terbentuk dr fosfat, gula dan alkohol

contohnya : - glukosa 6 fosfat dan fosfogliseraldehide

Reaksi transfer E  terjadi dlm reaksi fosforilasi Adenosin ~ P ~ P ~ P

ATP

Adenosin~P ~P

ADP

HO – R P – O – R E dipindahkan dengan group fosforil ke

senyawa lain dan menyebabkan senyawa aktif Macam-macam ikatan pyrofosfat kaya

1. ATP  sintesa pati

2. UTP  sintesa sukrosa 3. GTP  sintesa sellulosa

Ciri ikatan fosfat kaya E pada sel yang aktif bermetabolisme

 daur ulang (turn over) sangat tinggi

Sel bervacuola



2 pool fosfat

Metabolic pool



Citoplasma didominasi kloroplas ester fosfat

Nonmetabolic pool  vacuola ^

Pi Dominan

PERANAN P DALAM SEL

Suplai P terganggu  pertumbuhan terhambat



pelepasan P dr vacuola tertekan

Suplai P

Cukup  85 – 95 % Pi dalam vacuola

Diganggu [ P dlm vacuola] tajam [ P dlm sitosol] kecil

~ 6 mM  <3mM

PERAN PENGATURAN dr Pi

• Fungsi Pi

• 1. Pool metabolik

• 2. Pool non metabolik.

Fungsi P dalam pool metabolic

P terlibat dalam reaksi enzymatik.

Pi juga mengatur rekasi enzim kunci.

Pi dapat sebagai substrat (bahan) atau hasil akhir contoh ATP ADP + Pi

Kompartementasi (perpindahan tempat) Pi

penting utk mengatur jalur metabolisme dalam sitoplasma dan kloroplas

FUNGSI P DALAM METABOLISME

Pi vacuola  Pi sitoplasma Aktif fosfofruktokinase 

(enzym yg mengatur masuknya Senyawa ke jalur glicolisis)

respiratori burst 

Pemasakan buah cepat Sitoplasma

Vacuola

Pi

Pi <<<  kematangan tertunda

Contoh. Dalam jaringan buah tomat

Pi

1. Sintesa pati

ADP – glucosa +Pi  aktif pyrofosforilasi

triosefosfat  aktif

(TP) (PGA)

Ratio Pi/TP  laju sintesa pati (kloroplas) Tinggi  enzym ADP – G terhambat

glyseraldehide – 3 phosphat 2. Pelepasan TP

dihidroksiaseton – phospaat (produk fiksasi CO₂)

meninggalkan kloroplas

Pelepasan diatur fosfat translokator (dlm membran kloroplas) Pertukaran Pi dengan TP

Serapan Pi ke Kloroplas  mengatur pelepasan fotosintat ke sitoplasma

Mekanisme pengaturannya :

Jika serapan Pi ke kloroplast tinggi banyak TP yang keluar dari kloroplas ( [ TP ] dalam stroma rendah)

bahan

TP adalah sintesa pati

aktivator Sintesa pati <<<

PERANAN Pi dalam  Fotosintesis

Jika [ Pi ] dalam kloroplas >>>

TP (bahan utk RuBP) keluar ke sitoplasma TP dalam stroma <<<

RuBP <<< (penerima CO2) Fiksasi CO2 <<<

Konsentrasi P eksternal yang tinggi juga menghambat fiksasi CO2.

3. Pi dalam fotosintesis dan metabolisme karbohidrat

Hub. Antara fiksasi C, pembentukan pati dlm Kloroplas sebagai fungsi konsentrasi P external

Konsentrasi P Lar External (mM) 0.15 0.65 1.0 2.0 3.5

Total C Fixation

Incorp into starch 11.0 2.6

13.6 0.4

10.9 0.1

7.1 0.1

3.3 0.1

Pi dan metabolisme karbohidrat dan transport sukrosa

• ATP-UTP heksosa dan sukrosa ( Karbohidrat )

Pi  membentuk ATP / ADP. UTP

- perlu utk sintesa hexosa/sucrosa - perlu utk sucrosa proton

cotransport dlm phloem

• P<<<  transport E dr kloroplas bag lain 

•  sintesa protein & as nukleat 

•  pati & sukrosa akumulasi

•  gula fosfat dan adenilat 

Pi dengan metabolisme karbohidrat

P >>> kandungan pati dalam daun <<<

P<<<  leaf expansion 

 [ C ] dlm daun  eksport C dr daun 

Akumulasi karbohodrat 

P <<<  kurang sensitif thd UV – B light  akumulasi “flavenoids”

daun lebih tebal

kurang peka thd chy UV – B proses fotosintesis 

sugar starch protein

Suplai P, Pertumb Tan, Komposisi Tan

P  pertumbuhan optimal  0.3 – 0.5 % d w of plant P <<< -pertumbuhan terhambat

-warna kemerah-merahan antocyamin

-daun warna hijau gelap

-perpanjangan sel daun terhambat -klorofil/unit luas daun tinggi

-eff.fotosintesis/unit luas daun rendah

-respirasi, fotosintesis, pembelahan sel  Level P suplai selama reproduktif

- mengatur ratio pati/sukrosa dlm daun - mengatur pembagian fotosintat antara daun dan organ reproduktif

Tan legum yg – P

 suplai karbohidrat ke nodul <<<

muncul gejala kekurangan N P  keseimbangan fitohormon P  <<<   daun <<<

 saat pembungaan tertunda P <<< pembentukan buah & biji 

hasil <<<

qualitas <<<

P in Plant Nutrition

• Essential to plants and animals

• ATP, DNA, RNA

• Critical to energy flow in cells

• Usually 0.2 to 0.4% of dry matter

• Mycorrhizae critical to P uptake in most plants

• exudates

Phosphorus Sources

• Inorganic P Sources

• Rock Phosphate

• Bone Meal

• P fertilizer

• Organic-based P sources

• Green Manures - ?

• Manures

• Composts

• Composted Manures

• Composted Plant Biomass

Rock Phosphate as a P Source

• Rock phosphate (RP) is a slowly soluble P source from mined phosphate (calcium phosphates).

• Solubility is highly dependant on several factors

• Soil type

• Low pH

• Low Ca

• Low P fixing Capacity

Rock phosphate mine in India

Rock Phosphate as a P Source

• Phosphorus availability – relative response approaches 1:1

• Optimum soil and RP source

Source: Correa et al., 2005.

Sci. Agric. 62:159-164

Fertilizer P

• Rock phosphate contains hydroxyapatite and fluoroapatite that are not very soluble

• Treat with sulfuric and phosphoric acid to make triplesuperphosphate, which is very soluble

BFA Pupuk P BFA

H₂SO₄ H₂SO₄ H₂SO₄ H₂SO₄ H₂SO₄ H₂SO₄

H₃PO₄ H₃PO₄

NH₃

NH₃ NH₃

Normal Super Fosfat

0-20-0

TSP 0-46-0

Superfosfat beramonia

8-16-0 SP 36

0-36-0

Amonium Fosfat 11-55-0 18-46-0

Asam Super Fosfat

Amonium Polifosfat

Fosfat nitrat

Amonium Fosfat 11-55-0 18-46-0

NH₃

NH₃

HCl

Soil Phosphorus

• Derived from P bearing rocks & minerals

• Different forms: organic/inorganic, soluble/insoluble

• Very reactive: Fe, Al, Ca

• Limiting nutrient in many unfertilized,

acid soils

Inorganic fertilizers

• All mineral fertilizers originate from

mined geologic formations of the mineral apatite (rock phosphate).

• Rock Phosphate (0-20-0).

• Finely ground rock phosphate was

one of the first inorganic P fertilizer

used.

Inorganic fertilizers

• Its low P2O5 analysis and low solubility were

associated with high rates and costs when it was used.

• Although very little rock phosphate is currently used, it can be an important source of P on soils that have a high P fixing capacity or a single application is

desired to correct a severe soil deficiency in a small area such as a home landscape.

• Application to highly acid soils?

PUPUK P

• DSP (Double superfosfat) / DS / Ca(H₂PO₄)₂

• TSP (Triple superphosphate) / TS / Ca(H₂PO₄)₂

• SP-36

• FMP (Fused Magnesium Phosphate)

• Agrophos

• Fosfat cirebon

• Serbuk thomas

• Citraphos / CIRP

Common phosphate fertilizers with ammonium

• Monoammonium phosphate (MAP)

• NH₄H₂PO₄

• pH of 0.1M solution is 4.0

• H₂PO₄^- ↔ HPO₄^2- + H⁺

• Diammonium phosphate (DAP)

• (NH₄)₂HPO₄

• pH of 0.1M solution is 7.8

• HPO₄^2- ↔ H₂PO₄^- + OH^-

• Ammonium polyphosphate (APP)

• pH 6.0 – 6.5

• Hydrolysis reaction

Sauchelli, 1965

Photos courtesy of Agrium

Crop absorption of soil-P.

Crop absorption of soil-P.

Absorption is from just a thin cylinder of soil

around each root.

CaHPO₄ + H₂O ^<== = (dissolves slowly)  Ca²⁺ + HPO₄^2-

Plant uptake of broadcast, incorporated P Fertilizer.

Plant uptake of broadcast, incorporated P Fertilizer.

P Fertilizer

•Only 10 to 15 % of incorporated P fertilizer is absorbed by crop.

•85 to 90 % of P fertilizer reacts with soil to “build up” soil test.

Plant uptake of banded P Fertilizer.

Plant uptake of banded P Fertilizer.

Most of fertilizer P is used by crop and there is little soil test build-up.

Banded P-fertilizer Banded P-fertilizer Expanded sorption

Important P Considerations

• Banding reduces P fixation

• Immobile in soil under most conditions

• High levels - get movement of organics

• phospholipids, inositol phosphates, etc.

• could tie up Zn, but manure supplies Zn

• Erosion loss - greatest concern

• Conversions%P₂O₅ -> %P * 2.29

Methods of P fertilization

• Most common application of P fertilizers: Broadcast fertilizer over the soil surface and then incorporate it with a tillage

operation.

•

• Alternative: Band with the seed, or two inches below and to the side of the seed at planting.

• Broadcast-incorporation is less time consuming and is popular when large acreages must be fertilized and planted in a short period of time, or labor is scarce.

Methods of nutrient placement Methods of nutrient placement

Broadcasting

Broadcast TSP followed by “listing” (making beds)

Maricopa, AZ

Preplant Applications

• Broadcast

• Uniform distribution of dry or liquid

materials over the soil surface

• Can be mechanically incorporated

• Can be incorporated by rain or irrigation

Liquid manure from hog feeding being pumped onto farmland in Iowa, USDA-NRCS

Band Application

Surface band near transplanted broccoli, sprinkler-irrigated

Oregon

“Side-dressing” lettuce with liquid N fertilizer, Yuma

Nutrient Considerations

• Phosphorus

• Banding minimizes soil:fertilizer contact

• Minimizes reversion

• Banding is generally more efficient in soils with lower amounts of available P

• At higher levels of available P banding and broadcasting result in similar efficiencies

• Apply just before or at planting

• Less time for reversion to occur

Model Response Curve

Amount of Input Crop Response ^Maximum _Profit

Maximum Yield

Fertilizer Application

1. Preplant Application

-Lime, sulfur, superphosphate, gypsum, dolomite 2. Dry Application

- Fertilizers with solubility <20 g/100 ml - Top dressing

- Do not apply lime with phosphorus 3. Liquid Feeding

- Use soluble fertilizers

- Constant feeding vs intermittent feeding

P Based Application Rate

• Soil Test Phosphorus (STP)

• Application based upon soil test analysis, and crop P needs, based on university

recommendations

• Fertility strategy

• Buildup low P soils

• Maintenance

• Drawdown

TERIMA KASIH