bahan kajian mk. dasar ilmu tanah fosfat tanah

BAHAN KAJIANMK. DASAR ILMU TANAH

FOSFAT TANAH

www.marno.lecture.ub.ac.id

diunduh dari: ….. http://www.biocyclopedia.com/index/plant_nutrition/essential_elements_macronutrients/phosphorus/nature_and_transformations_of_soil_phosphorus.php

SIKLUS P DALAM TANAH PERTANIAN

Serapan Tanaman

P-organik

P- pupuk

P- mineral P- larutan

P- terserap

Pencucian & Runoff

sorpsi

desorpsi

pengendapan

pelarutan mineralisasi

imobilisasi

Problematik Fosfor

Jumlah sedikit yang terdapat dalam tanah

Ketidak-tersediaan fosfor yg sdh ada dalam

tanah

Adanya fiksasi fosfor yang menyolok

HUBUNGAN P-TANAH DAN TANAMAN

* Proses-proses Energi dan reproduksi

* Pertumbuhan dan perkembangan a Pertumbuhan akar A Kemasakan (pembentukan buah, biji

dan pembungaan,...)* Siklus bahan organik sangat menentukan

Senyawa P dalam tanah Senyawa P an-organik

1. Senyawa Kalsium2. Senyawa besi dan aluminium

Senyawa Rumus Kelarutan

Fluor-apatit 3 Ca3(PO4)2.CaFKarbonato-apatit 3 Ca3(PO4)2.CaCO3Hidroksi-apatit 3 Ca3(PO4)2.Ca(OH)2Oksi-apatit 3 Ca3(PO4)2.CaOTrikalsium-fosfat Ca3(PO4)2Dikalsium-fosfat CaHPO4 naikMonokalsium-fosfat Ca(H2PO4)2

Senyawa P-organik:1. Fitin dan derivatifnya2. Asam Nukleat3. Fosfolipida

Fosfat dan kualitas perairan

• Memicu terjadinya eutrofikasi• P memacu pertumbuhan algae

- may promote anoxia and lead to ‘dead’ zones

• P memasuki ke perairan dari sumber titik dan

sumber bukan-titik

Fiksasi Fosfat

* Membatasi ketersediaan P secara biologis

• P bereaksi sangat kuat dengan material tanah - membatasi ketersediaan fosfat - membatasi pergerakan fosfat dalam tanah - pergerakan terjadi melalui erosi tanah

• Menjerap dan mengendapkan fosfat

Reaksi-reaksi Adsorpsi = Penjerapan

Adsorpsi kuat pada tanah-tanah mineral

- adsorpsi pada oksida-oksida Fe- dan Al

- adsorpsi pada tepian patahan mineral liat silikat (terutama kaolinit)

Senyawa P-anorganik (mengendap)

Tanah-tanah masam 8 Fe dan Al fosfat

FePO4l2H2O, AlPO4

l2H2O

Tanah-tanah Alkaline

4 Ca dan Mg fosfat

â Ca(H2PO4)2 â monocalcium phosphate

â CaHPO4â dicalcium phosphate

â Ca3(PO4)2â tricalcium phosphate

â 3Ca3(PO4)2lCa(OH)2â hidroksi-apatit

â 3Ca3(PO4)2lCaCO3â Apatite karbonat

Kelarutan menurun

Senyawa P-anorganik

pH

6

8

Tata-nama anion fosfat

H3PO4 = phosphoric acid

H2PO4- = monobasic

HPO4-2 = dibasic

PO4-3 = tribasic

Fosfat paling tersedia pada kisaran pH 6 - 7

Oksida hidrous

P-Organik dalam tanah* Sekitar 20 - 80 % dari P-total dalam

tanah berupa P-organik* Kebanyakan berupa fosfat-inositol,

C6H6(OH)6

- sekitar 10 - 50 % dari P-organik - sebagian asam nukleat dan

fosfolipid

Salah satu bentuk P-organik dalam tanah adalah inositol-

hexaphosphate , jumlahnya dapat mencapay 50 % dari total P-

organik dalam tanah.

P-Organik

(P-tersedia)

Siklus : Mekanisme pelepasan lambat

HxPO4x-3

mineralisasi

imob

ilisa

si

Fase fosfat padatan(tidak-tersedia)

HUBUNGAN SIMBIOSIS :Fungi dan Tumbuhan

Infeksi mikorhiza akar, kunci penyerapan fosfat

Hifa fungi

Mikorhiza

Akar tumbuhan

Reaksi fosfat pada tanah alkalis pH tinggi

P berubah menjadi bentuk sukar larut senyawa-senyawa Ca dan Mg

Ca(H2PO4)2 + CaCO3 + H2O ® 2 CaHPO4·2H2O + CO2 mudah larut kurang-larut

6 CaHPO4·2H2O + 3 CaCO3 ® 3 Ca3(PO4)2 + 3 CO2 + 5 H2O

Kurang larut

3 Ca3(PO4)2 + CaCO3 ®3Ca3(PO4)2·CaCO3

sangat tidak larut

Masalah sangat serius pada tanah-tanah kapur di daerah

iklim kering

acid soils alkaline soils

Dinamika ion fosfat: Protonasi

Ketersediaan P anorganik dalam tanah

Kemasaman tanah (pH):Ketersediaan P bagi tanaman tgt pd bentuk anion fosfat, selanjutnya bentuk anion ini tgt pada pH

+ OH- +OH-

H2PO4- H2O + HPO4

= H2O + PO4---

larutan tanah larutan tanahsangat masam sangat alkalin

% kepekatan100

50 H3PO4 H2PO4- HPO4

= PO3-3

0 0 2 4 6 8 10 12 14

pH larutan

Paling tersedia bagi tanaman

Ketersediaan P-anorganik tanah masam

Pengendapan oleh kation Fe, Al, Mn

Al3+ + H2PO4- + H2O 2H+ + Al(OH)2H2PO4

larut tdk larut

Dlm tanah masam biasanya konsentrasi kation Fe, Al lebih besar dp anion fosfat, sehingga reaksi berlangsung ke arah kanan

Pengikatan oleh hidro-oksida: Fiksasi fosfat OH OH Al OH + H2PO4

- OH- + Al OH OH larut H2PO4 tdk larutHidro-oksida Al

Pengikatan oleh liat silikat: Kaolinit, Montmorilonit, Illit1. Reaksi permukaan antara gugusan OH- yang tersembul di permukaan liat dengan anion fosfat2. Kation Fe dan Al dibebaskan dari pinggiran kristal silikat yg kemudian bereaksi dengan anion

fosfat menjadi fosfat-hidroksi

[Al] + H2PO4- + 2H2O 2H+ + Al(OH)2H2PO4 Dlm kristal silikat tidak larut

Ketersediaan P-anorganik pd pH tinggi

Pengendapan oleh kation Ca++ atau CaCO3

H2PO4- + 2 Ca++ Ca3(PO4)2 + 4H+

larut tidak larut

H2PO4- + 2 CaCO3

Ca3(PO4)2 + 2CO2 + 2H2O larut tidak larut

Ca3(PO4)2 yang terbentuk dalam reaksi di atas, masih dapat berubah menjadi bentuk-bentuk yang lebih sukar larut, seperti senyawa hidroksi-, oksi- , karbonat-, atau fluor-apatit.Reaksi-reaksi ini semua terjadi pada tanah-tanah masam yang dikapur dengan dosis tinggi (Pengapuran berat)

Daya ikat P dari Tanah

Fosfor yang sangat lambat tersedia

Apatit, Fe-, Mn- dan Al-fosfat tua, Fosfat organik yang mantap

Fosfat yang lambat tersedia

Ca3(PO4)2, Fe-, mn-, dan Al-fosfat yg baru terbentuk, dan fosfat organik baru (sedang) dimineralisasikan

Hasil-hasil penelitian:1. Tanah-tanah di jawa Barat: Rata-rata 18.2 kuintal TSP dg kadar 46% P2O5 diikat oleh tanah setiap hektar lapisan olah.2. Tanah Latosol mempunyai daya ikat setara dengan 7.8 ton superfosfat dg kadar 20% P2O5.

Fosfat segera / mudah tersedia

Larut air : NH4-fosfat, Ca(H2PO4)2Tidak larut: CaHPO4 dan Ca3(PO4)2

Kemampuan tanah menjerap (Daya Jerap) P

Tanah Mineral Liat Perlakuan pH Daya Jerap P (*)

Latosol - Tanpa kapur 5.7 30.110Purwokerto Haloisit Dengan kapur 5.9 26.600

Latosol- Kaolinit Tanpa kapur 5.2 45.520Cibodas Dengan kapur 5.6 40.920

Podsolik- Smektit Tanpa kapur 4.8 36.950Gajrug Dengan kapur 5.3 33.180

Podsolik- Smektit Tanpa kapur 4.6 29.280Samarinda Kaolinit Dengan kapur 5.2 16.370

Grumusol- Smektit, Kaolinit Tanpa kapur 6.7 14.960Yogjakarta Haloisit

Andosol Bogor Alofan, Haloisit Tanpa kapur 4.6 33.360

Keterangan: (*) setara dengan kg superfosfat 20% P2O5 setiap HLOPengapuran setara dengan 0.5 SMPSumber: Djokosudardjo (1982)

Pengelolaan P - Tanah

Pengendalian P-tersedia dalam tanah: 1. Pengapuran 3. Pengendalian fiksasi P-tanah2. Penempatan pupuk

P-tanah Tersedia

Limbah tanaman Pupuk kandang

Pupuk buatan Mineral tanah

BOT

Tanaman Pencucian FiksasiErosi

Siklus Lambat P-anorganik

Siklus Cepat P-anorganik & Organik

Siklus Lambat P-Organik

P-mineral primer

(HCl-Pi)

P-mineral sekunder

(NaOH-Pi)(P-residu)

P-terfiksasi (Sonic-Pi)(P-residu)

P- larutan tanah

P- dalam tanaman & jasad tanah

P-terlarut labil (Resin-P)

P-terfiksasi labil (Bikarbonat-Po)

P-terlarut agak labil

(P-terfiksasi)(Bikarbonat-Pi)

P-terfiksasi agak labil

(NaOH-Po)

P-organik terfiksasi secara kimia dan fisika

(Sonic-Po) (Residu-Po)

Siklus Transformasi P-tanah (Hedley et al. 1982)

P- tanah P-anorganik:1. Fraksi aktif: Al-P, Fe-P dan Ca-P2. Fraksi tidak aktif:

P-terjerap (P-absorption)P-terselimuti (P-occluded)

P-organik1. Inositol fosfat, Fosfolipid, Asam nukleat, Nukleotida, Gula-fosfat2. P-organik menyumbang 30-50% dari P-total tanah3. Senyawa P-organik terdapat dalam humus dan tubuh jasad tanah4. P-organik dalam tanah berasal dari bahan organik

Penambahan bahan organik ke tanah bertujuan:1. Meningkatkan kandungan bahan organik tanah2. Sumber unsur hara N,P,K, dan lainnya3. Meningkatkan KTK tanah4. Mengurangi jerapan P melalui pembentukan senyawa kompleks dg oksida amorf5. Meningkatkan dan memperbaiki agregasi tanah & lengas tanah6. Membentuk khelate dengan unsur hara mikro7. Detoksifikasi Al8. Meningkatkan biodiversitas tanah.

1. No direct practical importance2. Sering dipakai sbg “Indeks Pelapukan”3. P-total topsoil menurun dengan intensitas pelapukan4. Tanah-tanah tropis mengandung sekitar 200 ppm5. Ultisol & Alfisol : < 200 ppm P6. Andepts umumnya 1000 - 3000 ppm P7. Vertisol umumnya 20 - 90 ppm P8. Entisol & Inceptisols: beragam p-totalnya9. Oxisols umumnya < 200 ppm P10. …..

1. P-organik = 20-50 % total P-tanah2. Oxisols, Ultisols, Alfisols: P-organik = 60-80% P-total3. C:P rasio dalam tanah = 240:1 -- 110:14. N:P rasio dlm tanah = 20:1 -- 9:15. Mineralisasi P-organik sukar diukur, karena ion H2PO4-

yg dilepaskan ke tanah dengan cepat difiksasi menjadi bentuk-bentuk P-anorganik

6. Pemupukan N dan P mempercepat mineralisasi P-organik

7. P-organik dlm tanah menjadi sumber P yg penting bagi tanaman kalau tidak ada pemupukan P.

BAHAN ORGANIK SUMBER P

Komponen kualitas bahan organik sebagai sumberP: 1. Nisbah C/N (nilai kritisnya 25-30)2. Nisbah C/P ( < 200: mineralisasi P

> 300 : imobilisasi P)3. P-total4. Kandungan lignin dan polifenol5. Kapasitas polifenol mengikat protein 6. Indeks jangka-pendek pupuk hijau: C/N, kandungan lignin dan polifenol

1. Kandungan lignin dan polifenol yang rendah mempercepat laju mineralisasi P2. Bahan organik dengan kandungan P lebih dari 2500 ppm akan terjadi

mineralisasi P dan menurunkan jerapan P-tanah3. Lignin merupakan senyawa polimer pd jaringan tanaman berkayu, sulit

dirombak oleh mikroba tanah

Polifenol merupakan senyawa aromatik-hidroksil : a. Polifenol larut air & Polifenol tdk larut airb. Polifenol berat molekul rendah & berat molekul tinggi …… tanin

Polifenol mampu mengikat protein dan ensim dari jasad dekomposer, sehingga menghambat laju dekomposisi bahan organik oleh jasad renik tanah

1. P - ANORGANIK: Fraksi aktif & Fraksi tidak aktif2. Fraksi aktif : Ca-P, Al-P dan Fe-P3. Fraksi tdak-aktif : Occluded-P dan Reductant-soluble P4. Occluded-P : senyawa Fe-P dan Al-P yang dibungkus oleh

selubung inert.5. Rs-P : Senyawa P yg dibungkus oleh selubung dari bahan

yang dpt larut pd kondisi anaerobik6. Transformasi bentuk-bentuk P-tanah dikendalikan pH7. Ca-P lebih mudah larut dp Fe-P dan Al-P8. Rezim air sgt berpengaruh thd transformasi P-tanah 9. Kondisi AQUIK ---- Akumulasi Al-P10. Kondisi USTIK ------ Akumulasi Fe-P

Faktor Retensi P

dalam tanah

TIPE LIAT Tanah-tanah liat lebih banyak meretensi & memfiksasi p-pupuk daripada tanah berpasirLiat silikat tipe 1:1 mempunyai kemampuan lebih besar me-”retensi” P dibanding liat tipe 2:1Tanah yang kaya liat kaolinitik akan “mengikat” lebih banyak P -pupuk daripada tanah yang kaya liat tipe 2:1Adanya liat oksida hidrous dari Fe dan Al juga terlibat dalam retensi P-pupuk

TIME OF REACTIONSemakin lama P-pupuk kontak langsung dengan tanah akan semakin besar jumlah retensi & fiksasi PHal ini dapat terjadi karena adanya proses dehidrasi dan reorientasi-kristal yg melibatkan hasil fiksasi P

Implikasi penting adalah waktu pemupukan P dan penempatan pupuk P dalam tanah.

Bgm pd tanah yg mempunyai kapasitas fiksasi P tinggi ? …………..Bgm pd tanah yg mempunyai kapasitas fiksasi P rendah? …………

Faktor Retensi P

dalam tanah

pH TANAH Kisaran pH tanah yg optimum bagi ketersediaan p-tanah adalah 5.5 - 7.0Pd tanah dg pH rendah, retensi terjadi karena adanya reaksi fosfat dengan Fe, Al dan oksida hidratnya.Pd tanah dg pH tinggi, retensi fosfat terjadi karena reaksi fosfat dengan Ca dan Mg dan karbonatnya

TEMPERATURTanah di daerah iklim panas (warmer) memfiksasi fosfat lebih banyak dp tanah-tanah di daerah iklim sedang (temperate). Tanah di daerah iklim panas ini mengandung lebih banyak oksida-oksida hidrat dari Fe dan Al.

BAHAN ORGANIKDekomposisi bahan organik menghasilkan CO2; gas ini bersenyawa dg air menjadi asam karbonat; asam ini mampu men-dekomposisi mineral primer yang mengandung fosfat.Ekstrak humus dari tanah mampu meningkatkan kelarutan fosfat, krn:1. Pembentukan kompleks phosphohumic yg lebih mudah diambil tanaman2. Penggantian anion fosfat oleh humat3. Penyelimutan partikel sesquioksida oleh humus, membentuk selimut protektif sehingga mereduksi kapasitas fiksasi fosfat…………………………..

Faktor Retensi P

dalam tanah

BAHAN ORGANIK Lanjutan ……. Dekomposisi bahan organik menghasilkan anion-anion yang mampu membentuk senyawa kompleks dengan Fe dan Al, sehingga kation-kation ini tidak bereaksi dengan fosfatAnion-anion organik ini juga mampu melepaskan fosfat yang difiksasi oleh Fe dan AlAnion-anion yang efektif menggantikan fosfat tsb adalah sitrat, oksalat, tartrat, malat, dan malonat.

STATUS FOSFOR dalam TANAHTingkat kejenuhan fosfat dalam tanah atau jumlah fosfat yg telah difiksasi oleh tanah sangat menentukan besarnya fiksasi fosfat dari pupuk P.Rasio R2O3 : P2O5 mrp ukuran jumlah fosfat yg ada dalam tanah terhadap jumlah oksida Fe dan Al.

Nilai Rasio yang besar, berarti tanah miskin fosfat atau nilai kejenuhan fosfat rendah; sehingga fiksasi fosfat dari pupuk P sangat besarOleh karenanya tanah-tanah yag dipupuk fosfat dosis tinggi selama bertahun-tahun kemungkinan akan:1. Mereduksi dosis pupuk P saat ini2. Menggunakan lebih banyak fosfat yg ada dalam tanah3. Kombinasi keduanya

…………………..

Fiksasi P-pupuk , % 100

80

60

40

20

Pasio R2O3 : P2O5

1. Proses yg mengubah ketersediaan P-tanah yg diukur dengan pertumbuhan tanaman

2. Transformasi monokalsium fosfat (superfosfat) yg soluble menjadi Ca-P, Fe-P dan Al-P yg kurang soluble

3. Pada tanah alkalis: Ca-P dan Mg-P yg insoluble4. Pd tnh masam: Fe-P dan Al-P yg insoluble5. Al+++ + mono-kalsium fosfat ------ Al(OH)2H2PO4 (liming with phosphorus)6. Kapasitas fiksasi P = F(oksida Fe dan Al; Aldd)7. Intensitas Fiksasi P: Oksida > Oksida > Liat 1:1 > Liat 2:1 amorf kristalin

Tanah Liat dominan % Liat Fixed P (ppm) Adsorpsi Max. Pd 0.2 ppm P lrt tnh

Inceptisol Montmorilonit 27 106 83Ultisol Kaolinit 38 480 360Oxisol Kaolinit 36 531 395Andept Alofan 11 1050 670

Sumber: NCSU, 1973

1. H2PO4- dlm larutan tanah < 10 ppm, dlm tanaman 2000 ppm

2. Konsentrasi optimum unt jagung dan buncis:0.07 ppm pd tnh berliat Ultisol , Oxisol0.2 ppm pd tnh berpasir

3. Konsentrasi keseimbangan P dlm larutan tnh akibat aplikasi pupuk fosfat sgt penting ….. “P-fixation isotherm”: mengevaluasi derajat fiksasi dan pelepasan P pd suatu saat

4. Mineralogi liat tanah sgt menentukan kapasitas fiksasi P5. Liat oksida & Alofan > Kaolinit > Montmorilonit6. Uji tanah untuk P : mengekstraks sejumlah P-tersedia dlm

tanah yg berkorelasi dg respon tanmn thd pemupukan P7. Tingkat kritis hasil uji tanah sekitar 0.07 - 0.2 ppm P dlm

larutan tanah

REAKSI P tanah

ALKALINE

PRESIPITASI DIKALSIUM FOSFAT Pada kondisi Ph tanah yang tinggi dan kaya kalsium, terjadi pengendapan senyawa-senyawa:1. Kalsium fosfat: Ca3(PO4)2; CaHPO42. Hidroksi-apatit3. Karbonat-apatit

PRESIPITASI PERMUKAAN PADATAN KALSIUM KARBONAT

Ion-ion fosfat yang kontak dengan permukaan padatan kalsium karbonat akan diendapkan pd permukaan partikel ini. Hasil akhir dari reaksi ini adalah garam-garam tidak larut dari kalsium, fosfat, dan mungkin CO3= atau OH-

Reaksi retensi fosfat oleh liat-liat yang jenuh kalsium: Liat-Ca-H2PO4

Tiga faktor penting:1. Aktivitas Ca++2. Jumlah dan ukuran partikel CaCO3 bebas3. Jumlah liat yang ada dlm tanah

…………………..

P-aded (ppm) 1200

1000

800

600

400

200

0.001 0.01 0.05 0.1 0.2 1.0 P dlm larutan tanah, ppm

Oxisol, 45% liat

Andept

Ultisol , 38% liat

Tnh Montmorilonit, 40% liat

Sumber: Fox, 1974

Tanaman Hasil, t/ha P-removal, kg/ha

1. Jagung Biji : 1.0 6Jerami : 1.5 3Biji : 7.0 20Jerami : 7.0 14

2. Padi Biji : 1.5 7Jerami : 1.5 1Biji : 8.0 32Jerami : 8.0 5

3. Nanas Buah : 12.5 2.3

4. Tebu 2 th Above ground: 100 20300 35

Sumber: Sanchez, 1976.

Hasil relatif (%) 100

80

60

40

20

0.003 0.006 0.050 0.100 0.200 0.400 1.600 P- larutan tanah, ppm

Ubijalar: toleran tanah miskin P

Jagung: intermediate

Lettuce: In-tolerant

Tanaman P-larutan tnh yg menghasilkan 95% hasil maks., ppm

1. Lettuce 0.402. Tomat 0.253. Cucumber 0.204. Kedelai (vegetable) 0.205. Ubijalar 0.106. Jagung 0.607. Sorghum 0.508. Kubis 0.04

Sumber: Fox et al. (1974)

Tanaman Internal P Requirement, %P

1. Stylosanthes humilis 0.172. Centrosema pubescens 0.163. Desmodium intortum 0.224. Digitaria decumbens 0.165. Panicum maximum 0.196. Pennisetum clandestinum 0.227. Paspalum dilatatum 0.258.

Sumber: Andrew & Robins (1969, 1971)

TEKNOLOGI PEMUPUKAN FOSFAT :

1. Respon pupuk P sgt tinggi pada Oxisol, Ultisol, andepts, Vertisols2. Dosis pupuk P = F (jenis tanaman, tanah, cara aplikasi, musim)3. Dosis Rekomendasi Jagung, kedelai, Tebu: 100 - 150 kg P2O5/ha4. Kapasistas fiksasi P tanah menentukan cara aplikasi pupuk P:

Disebar, ditugal, digarit, pd lubang tanam, dll5. Pada tanah yg memfiksasi P ada dua strategi:

1. Dosis medium, digarit, setiap musim tanam2. Dosis tinggi unt menjenuhi kapasitas fiksasi P-tanah, dan

efek residunya berlangsung beberapa tahun6. Pupuk P yg baik harus mengandung 40-50 % P dlm bentuk larut air ,

untuk memenuhi kenbutuhan awal pertumbuhan tanaman7. Aplikasi kapur & silikat mampu menurunkan fiksasi P dlm tanah8. Pengapuran hingga pH 5.5 - 6.0 umumnya meningkatkan ketersediaan

P dalam tanah, mengurangi fiksasi P

Hasil biomasa , % 100

80

60

40

20

0 115 230 460 Pemupukan P (ppm P)

Sumber: Mendez-Lay (1974), Tnh Oxisol.

Tingkat kritis

Tdk dipakur pH= 4.8

Dikapur hingga pH = 5.5

Kapasitas fiksasi P tanah sngt tinggi, alternatif pengelolaan:

1. Kombinasi cara aplikasi pupuk P: ditugal/digarit dg sebar2. Batuan-fosfat larut sitrat3. Aplikasi kapur atau Ca-silikat unt ngurangi fiksasi P4. Kultivar tanaman yg toleran thd larutan tanah yg miskin

fosfat5. Pertimbangan biaya pupuk & pemupukan.

PERILAKU PUPUK P

dalam TANAH

AMMONIUM FOSFAT Dalam tanah, senyawa ammonium fosfat akan bergerak ke luar dari granula pupuk; kalau dalam tanah terdapat banyak Ca++, maka akan terbentuk dikalsium fosfat.

MAP : Mono ammonium fosfat (larutan jenuh punya pH 4.0)DAP : Di ammonium fosfat ( larutan jenuhnya punya pH 9.0)

PRESIPITASI PERMUKAAN PADATAN KALSIUM KARBONAT

Ion-ion fosfat yang kontak dengan permukaan padatan kalsium karbonat akan diendapkan pd permukaan partikel ini. Hasil akhir dari reaksi ini adalah garam-garam tidak larut dari kalsium, fosfat, dan mungkin CO3= atau OH-

Reaksi retensi fosfat oleh liat-liat yang jenuh kalsium: Liat-Ca-H2PO4

Tiga faktor penting:1. Aktivitas Ca++2. Jumlah dan ukuran partikel CaCO3 bebas3. Jumlah liat yang ada dlm tanah

…………………..

MONO KALSIUM FOSFAT

Granula Monokalsium fosfat:

H2O H2O

H2O

Consentrated medium, pH 1.5, dimana CaH2PO4 dan CaHPO4 bergerak ke luar

Melarutkan Fe, Al, dan Mn

Pembentukan besi-fosfat, Al-fosfat, Mn-fosfat yg mengendap

MnPO4 FePO4

AlPO4

NILAI KOMPARATIF

PUPUK FOSFAT

1. Bentuk fosfat yang tersedia bagi tanaman ada dua, yaitu Fosfat-Larut-Air dan Fosfat-Larut-Sitrat. Namun demikian respon tanaman terhadap kedua bentuk fosfat ini sangat beragam.

2. Untuk mendapatkan hasil maksimum bagi tanaman semusim yg sistem perakarannya terbatas, umumnya diperlukan pupuk P yang banyak mengandung fosfat-larut-air.

3. Untuk tanaman perennial yang sistem perakarannya luas (ekstensif), tingginya tingkat kelarutan fosfat dalam air (>60%) tidak menjadi faktor penting.

4. Untuk tanaman jagung, terutama pada saat awal pertumbuhannya, memerlukan fosfat yang larut air.

5. Kalau jumlah pupuk fosfat terbatas, respon tanaman paling baik akan diperoleh kalau pupuk fosfat tsb mudah larut air dan penempatan pupuk di dekat benih atau bibit. Hal seperti ini sangat penting bagi tanah-tanah yang miskin fosfat.

6. Pada tanah masam hingga netral, pupuk P granuler yg mudah larut air, biasanya lebih efektif daripada pupuk P yang berupa bubukan, kalau pupuk dicampur dg tanah. Pada batas-batas kondisi tertentu, semakin besar ukuran granula pupuk, efektifitasnya semakin baik.

7. Pada tanah netral hingga masam, “band application” bubukan pupuk P yg mudah larut air akan memberikan hasil yg lebih baik dibandingkan dg pemakaian pupuk yg dicampur dengan tanah.

NILAI KOMPARATIF

PUPUK FOSFAT

8. Pada tanah-tanah berkapur, pupuk fosfat larut air yg berbentuk granula seringkali memberikan hasil lebih baik. Pupuk fosfat-nitrat granuler yg kelarutan airnya rendah (<50%) tidak cocok untuk tanah-tanah berkapur.

9. Hasil terbaik dapat diperoleh dengan bahan-bahan yg kelarutan airnya rendah, kalau diberikan dalam bentuk bubukan dan dicampur dengan tanah berkapur

10. Monoammonium fosfat (MAP) umumnya lebih cocok untuk tanah-tanah berkapur dibandingkan dengan DAP

11. Pupuk fosfat yg sukar larut air, efektivitasnya menurun dengan semakin besarnya ukuran partikel (granula) pupuk.

12. Pupuk fosfat proses thermal, kalau ditumbuk halus, dapat menjadi sumber P yang sesuai untuk banyak tanaman pada tanah masam; tetapi umumnya tidak berhasil untuk tanah netral dan alkalin.

13. Respon maksimum thd pemupukan P tidak akan terjadi kalau tidak dibarengi dengan penambahan sejumlah unsur lain (termasuk unsur hara sekunder dan mikro).Hasil-hasil penelitian menunjukkan bahwa penggunaan P oleh tanaman dapat diperbaiki oleh adanya sulfat dan ammonium di dalam bahan pupuk.

MEKANISME PENJERAPAN FOSFAT

“Adsorption” terjadi kalau ion fosfat terusir dari

larutan tanah dan menjadi terikat pada permukaan partikel tanah. Kalau ion

fosfat yang terjerap itu kemudian mengalami

“difusi” ke dalam padatan, maka ia disebut

“terserap”.

Some authors use the term“penetrated phosphate” to avoid confusion between adsorbed and absorbed;

“sorption”covers the combined

processes.

Diunduh dari: ……… 27/3/2013

ABSORPSI & OKLUSI P-TANAH

Absorpsi P-terjerap ke

dalam mineral tganah (a)

dan

Oklusi lebih lanjut P-terjerap

b)

Diunduh dari: ……… 27/3/2013

Mineral tanah

Mineral tanah

larutan tanah

P terjebak oleh selimut

Selimut oksida Fe

atau Al

Dinamika P-tanah, termasuk tranformasi dan perilaku P dari pupuk fosfat.

Pergerakan P-tanah snagat terbatas, sehingga

penempatan pupuk P dalam tanah snagat kritis dalam

mencapai efisiensi serapannya.

Banded applications of fertilizer P have proven the

most effective thereby minimizing surface contact with the soil which tends to decrease the solubility of the

applied P. Faktor lain yg berpengaruh adalah kesehatan tanaman, tdk ada penyakit, dan tanah

yg hangat.

Diunduh dari: http://www.extension.org/pages/9873/phosphorus-p ……… 27/3/2013

PO4 terlarutLarutan Tanah

BO hidup ----- BO mati

Erosi tanah

BinatangTanamanTanamanPupuk kimia

PO4 terjerap

PO4 mengendapFe, Al, Ca

Mineral tanah

RabukKomposHumusSistem

Tanah

Diunduh dari: http://www.sciencedirect.com/science/article/pii/S0166248110340116 ……… 27/3/2013

SIKLUS P DALAM TANAH (Dean Hesterberg, 2010)

P-mineralCa-fosfatFe-fosfatAl-fosfat

P-terjerapP-teroklusi

PO4-Fe-oksidaPO4-Al-oksidaPO4-Fe Al-BO

Residu P-organik(3% dari Pt)

P-humus(15-60% dari Pt)

P-biomasa mikroba

(0.4 – 7.5% dari Pt)

P biomasa tanaman(0.2-0.6% Pt bagian

di atas tanah)P-panen tanaman

Bahan pembenah(0.8-2.4% Pt

(pupuk, rabuk, biosolid)

P-runoff (<0.15% Pt)Terlarut dan partikulat

Bentuk-bentuk P yang ada dalam tanah.P dalam tanah dapat

dikelompokkan menjadi tiga “pool” yg berbeda tingkat ketersediaannya

bagi tanaman.

These pools are the readily available P (soil solution), the pool of P that is rapidly released

from the soil to replenish the soil solution (labile pool), and the relatively slowly available P (non-

labile)

Diunduh dari: http://www.grdc.com.au/Research-and-Development/GRDC-Update-Papers/2009/02/THE-SCIENCE-OF-PHOSPHORUS-NUTRITION-FORMS-IN-THE-SOIL-PLANT-UPTAKE-AND-PLANT-RESPONSE ……… 27/3/2013

P-larutan

P-labilP

Tidak labil

(Sumber: Sharpley and

Sheffield, Livestock and

Poultry Environmental

Stewardship Curriculum)

Diunduh dari: http://passel.unl.edu/pages/informationmodule.php?idinformationmodule=1118084123&topicorder=5&maxto=7 ……… 27/3/2013

SIKLUS P-TANAHPanen

Tanaman

Sisa panen

Aplikasi Pupuk P

Aplikasi P Rabuk

P-AnorganikP-OrganikP- Uji Tanah

P-larutan Labil StabilLabilStabil

Tanaman

Kesetimbangan P dalam tanah

Kalau P diserap ke dalam tanah setelah aplikasi

pupuk, risiko

kehilangan P-larut ke dlaam runoff akan

semakin berkurang (menurun)

dnegan waktu.

(Sumber: Image courtesy

of Charles Wortmann)

Diunduh dari: http://passel.unl.edu/pages/informationmodule.php?idinformationmodule=1118084123&topicorder=5&maxto=7 ……… 27/3/2013

P - larutan

P - larutan

P - larutan

Stabil ---- Labil

Stabil ---- Labil

Stabil ---- Labil

P-rabuk sebagian besar P-labil + P-larutan

P-rabuk bereaksi dnegan bahan organik tanah dan senyawa-senyawa Fe, Al dan Ca fosfat menjadi kurang tersedia

SIKLUS P DALAM TANAH

Diunduh dari: http://www.env.go.jp/en/wpaper/1995/eae240000000010.html ……… 27/3/2013

Tanaman

Akar Tanaman Sisa Tanaman

P larut air

Reaksi penjerapan

(adsorpsi) asam fosfat

P-organik mudah lapuk

P-organik agak sukar

lapuk

P-organik sukar lapuk

P-organik stabil

bergabung dengan

liat

Batuan fosfat

Asam fosfat dg Ca, Al, Fe

Oksida, dan asam

fosfat dalam liat

SUMBER : "Kikan Kagaku-sosetsu, 4" (Quaterly Chemistry 4), Science Society of Japan, ed., "Chemisory of Soil"

Apakah P-tanah itu?

Phosphorus (P), unsur hara esensial bagi tanaman. Unsur hara ini sangat kritis karena konsentrasinya dalam tanah

snagat rendah ( 600 ppm total P) dan kelarutannya snagat rendah (rata-rata 0.05 mg P L-1 dalam

larutan tanah). Soil P exists in inorganic and

organic forms. Inorganic forms are associated with amorphous and crystalline aluminium and iron compounds in acid soils and calcium compounds in

alkaline soils.

Bentuk-bentuk P-organik berhubungan dengan bahan

organik dalam tanah.

Diunduh dari: http://www.gnb.ca/0173/30/0173300016-e.asp ……… 27/3/2013

RabukPupuk

P-anorganik(P-terikat pd

mineral)P-Organik

(Bahan organik)

Tanaman yang

sedang tumbuh

Kehilangan P melalui erosi

tanah

Kehilangan P melalui

pencucian

P-larutan:

Options for managing soil phosphorus supplyDr. Ann McNeill

School of Earth & Environmental Sciences, University of Adelaide, South Australia. 21st July 2008

Maintenance of available phosphorus (P) levels in soil is a problem faced by all producers. There are potential agronomic strategies to assist

in sustainable management of the soil P resource in pasture-based farming enterprises. Firstly some background information about the P cycle is provided and the role of soil organic matter and microbes is

highlighted.

Tiga alternatif pengelolaan P adalah; 1. Impor P sebagai pupuk, yaitu pupuk mineral atau organik,2. Praktek untuk meningkatkan siklus P tanah untuk mendorong

sinkronisasi pelepasan dan serapan P-tersedia oleh tanaman3. Memaksimumkan efisiensi pemanfaatan P oleh tanaman.

Diunduh dari: http://www.grasslands.org.au/resources/Articles/NewsletterArticle1.html ……… 27/3/2013

Options for managing soil phosphorus supplyDr. Ann McNeill

School of Earth & Environmental Sciences, University of Adelaide, South Australia. 21st July 2008

Diunduh dari: http://www.grasslands.org.au/resources/Articles/NewsletterArticle1.html ……… 27/3/2013

Soil P cycle - pools and pathways. Modified from [McLaughlin et al. 1999, 1]

Cadangan biomasa mikroba

Po Labil

Po tidak-LabilFASE ORGANIK

Pi dapat ditukar

Pi tidak-dapat ditukarMINERAL

CADANGAN LARUTAN TANAHP -Organik + anorganik

Pertukaran kontak

AdsorpsiDesorpsi

Pengendapan

Asimilasi Dekomposisi BO

Mineralisasi Non-asimilatory

Mineralisasi

ImobilisasiPenyerapan akar

ekskresi akar

The value of phosphorus in crop stubbleSarah Noack1, Mike McLaughlin, Ron Smernik, Therese McBeath and Roger Armstrong

1The University of Adelaide

Phosphorus within the stubble can be released

directly to soil as soluble P (where it can be used immediately

by the crop or chemically fixed onto

the soil) atau

Diserap oleh mikroba dan selanjutnya

dilepaskan kembali ke tanah dalam waktu

mendatang.

Diunduh dari: http://www.grdc.com.au/Research-and-Development/GRDC-Update-Papers/2012/02/The-value-of-phosphorus-in-crop-stubble ……… 27/3/2013

P mikroba

P labil

P larutan

P tdk tersedia

P dalam

Tanaman

P dalam

Seresah sisa panen

KETERSEDIAAN P DALAM TANAH

Fosfat mudah diikat dna menjadi bagian dari senyawa kalsium, besi dan aluminum dalam tanah:

1. Only 10 - 30% of phosphate fertilizer is used in the year it is applied

2. 1/3 to 1/2 of the phosphate (P) fertilizer applied may never be recovered

3. P is most available in soils with a neutral pH (it is quickly tied up with pHs above or below)

4. Tanah-tanah yg kaya debu atau liat mengikat lebih banyak P5. Semakin rendah lengas tanah = semakin rendah ketersediaan P6. Semakin rendah suhu tanah = semakin rendah ketersediaan P

Diunduh dari: http://www.bioag.novozymes.com/en/products/canada/aboutphosphate/soil-phosphate/availability-in-cold-soils/Pages/default.aspx ……… 27/3/2013

KETERSEDIAAN P DALAM TANAH

P-larutan berbentuk ortofosfat. Molekul ini terdiri atas atom P (bulatan kuning)

dikelilingi oleh empat atom oksigen

(bulatan merah).

Diunduh dari: http://www.bioag.novozymes.com/en/products/canada/aboutphosphate/soil-phosphate/availability-in-cold-soils/Pages/default.aspx ……… 27/3/2013

P - larutan

Ion ortofosfat sekunder:HPO4= (pH>7.0)

Ion ortofosfat primer:H2PO4- (pH<7.0)

Bentuk yg lazim ditentukan oleh pH tanah, kedua bentuk ion seimbang pd

kondisi netral

Hubungan antara serapan P-tanaman dgn P-tersedia dalam tanah akibat aplikasi TSP dan PR ke tanah masam

When a water-soluble P fertilizer, e.g. TSP, is applied to acid soil containing oxides of iron (Fe) and aluminium (Al),

reaction products in the form of Fe-Al-P are the sources of

available P through desorption/dissolution processes

for uptake by the plant.

Kalau jumlah P yg terekstraks oleh uji tanah (k1’) seimbang

(korelasinya kuat) dengan jumlah P yg diserap oleh tanaman (k1) atau hasil

tanaman, maka uji tanah ini cocok untuk kalibrasi

rekomendasi dosis pupuk berdasar P-larut air.

Diunduh dari: http://www.fao.org/docrep/007/y5053e/y5053e0b.htm ……… 27/3/2013

IKTISAR FOSFAT -

TANAH

1. P dalam tanah berbentuk organik dan an-organik. Konsentrasi P-anorganik (H2PO4- dan HPO4=) dalam larutan tanah merupakan faktor sangat penting yg menentukan ketersediannya bagi tanaman

2. Konsentrasi ion fosfat dlm larutan tanah ditentukan oleh kecepatan reaksi imobilisasi biologis dan reaksinya dg fraksi mineral tanah. Tanah berliat (terutama liat tipe 1:1 dan oksida hidrous Fe an Al) memfiksasi ortofosfat menjadi bentuk yg tidak tersedia bagi tanaman.

3. Tanah berkapur umumnya mempunyai ketersediaan P rendah. Ion fosfat dijerap pada permukaan partikel halus kalsium karbonatdan selanjutnya dikonversi menjadi bentuk apatit yg tidak larut, atau mengalami proses pengendapan langsung dari larutan tanah menjadi kalsium fosfat.

4. Ketersediaan pupuk fosfat larut air dapat ditingkatkan dengan jalan menempatkan bahan pupuk secara “banding” dlm tanah (ditugal atau digarit). Hasil yag serupa dapat diperoleh dengan jalan granulasi bahan pupuk.

5. Terminologi khusus untuk pupuk fosfat adalah: Larut air, Larut sitrat, Tersedia, dan Total Fosfat.

IKTISAR FOSFAT -

TANAH

6. Pupuk fosfat dapat diklasifikasikan berdasarkan proses pembuatannya, menjadi: Heat-processed phosphate, dan Acid-treated Phosphate.

7. Reaksi pupuk fosfat larut air dengan berbagai komponen tanah menghasilkan “produk reaksi pupuk - tanah”. Kelarutan hasil reaksi inilah yang menentukan ketersediaan fosfat bagi tanaman

8. Kandungan air tanah sangat menentukan efektifitas dan laju ketersediaan pupuk fosfat. Pada kondisi air tanah kapasitas lapangan sekitar 50-80 % fosfat larut air dapat bergerak ke luar dari granula pupuk dalam periode 24 jam.

UJI P-TANAH:PRINSIP DAN ANALISISNYA

Soil Test Phosphorus: Principles and OverviewJ. Thomas Sims, University of Delaware

The fundamental goal of soil P testing has always been to identify the “optimum” soil test P concentration required for plant growth. The need for additional fertilization or manuring, and the economic return on an

investment in fertilizer P, could then be predicted.

Menurut Sims et al. (1998), tujuan lain dari uji P-tanah adalah :

1. Menentukan “indeks” kapasitas tanah mensuplai P, shg dapat mengestimasi waktu sebelum melakukan pemupukan fosfat diperlukan lagi.

2. Mengelompokkan tanah, dalam hal respon ekonomis terhadap pupuk P, berdasarkan sifat fisika dna kimia tanah,

3. Mengidentifikasi apakah tanah berkelebihan P sehingga menjadi sumber pencemaran bagi perairan.

Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013


Menurut Bray (1948), uji P-tanah yg bermanfaat secara agronomis harus mempunyai karakteristik:

1. Uji tanah harus mampu mengekstraks semua atau sebagian P-tersedia dalam tanah yang beragam sifat kimia dan mineralogisnya.

2. Uji tanah harus akurat dan cepat.3. The P extracted by the soil test should be well correlated with plant P

concentration, plant growth, and the response of the plant to added P in fertilizers or manures.

4. Uji tanah harus dapat secara akurat mendeteksi perbedaan konsnetrasi P-tanah akibat pemupukan sebelumnya.



Komponen mendasar dalam program uji P-tanah.


Komponen Uji P tanah

Definisi dan pertimbangan umum

Sampling Tanah Collection of a sample that accurately represents the area of interest is the first step in an effective soil testing program. Soil samples are normally collected from the “topsoil” or “plow layer” (0-20 cm depth), although this may vary with type of crop and intent of the test. In most cases ~20-25 individual soil cores are collected from a field that is no larger than 10-15 hectares. These cores are then composited to produce one sample that is submitted to the laboratory for analysis. Soil sampling patterns should reflect natural differences in soils (e.g., soil series) and any management practices or historical activities likely to affect soil test results (e.g., crop rotation, manuring, tillage practice).

Sampel tanah:Penanganan dan penyiapannya

Care should be taken during soil sample handling to avoid contamination from sampling and mixing devices. After collection, soil samples should be submitted as soon as possible to the laboratory where they are normally air-dried and ground or crushed to pass a 2mm sieve prior to analysis. Providing as much information as possible with the sample (e.g., previous fertilizer use, intended management plans, soil series) helps to ensure an accurate recommendation.



Komponen Uji P tanah

Definisi dan pertimbangan umum

Analisis sampel tanah

From an agronomic perspective, the purpose of soil analysis is to chemically “extract” the amount of nutrient from the soil that is proportional to that which will be available to the crop during the growing season. Since many different soil testing methods exist, it is vital that the analytical procedures selected are appropriate to the geographic region of interest and for the intended use of the soil.

Interpretasi hasil analisis

The ultimate goal of soil testing is to provide the user with a recommendation as to the likelihood that the application of nutrients in fertilizers or manures will provide a profitable increase in crop response. Recommendations based on soil testing results are developed using crop response data that have been obtained within a state or region with similar soils, cropping systems, and climatic conditions. Therefore, it is important to submit samples to a laboratory that is familiar with the crops to be grown and the soils and management practices that will be used.

Komponen mendasar dalam program uji P-tanah.

Soil Test Phosphorus: Bray and Kurtz P-1J. Thomas Sims, University of Delaware

The Bray and Kurtz P-1 soil test phosphorus (P) method was developed by Roger H.Bray and Touby Kurtz of the Illinois Agricultural Experiment Station in 1945 and is now widely

used in the Midwestern and North Central United States (Bray and Kurtz, 1945; Frank et al., 1998). Phosphorus extracted by the Bray and Kurtz P-1 method has been shown to be well-

correlated with crop yield response on most acid and neutral soils in these regions. For acid soils, the fluoride in the Bray and Kurtz extractant enhances P release from aluminum phosphates by decreasing Al activity in solution through the formation of various Al-F complexes. Fluoride is also effective at suppressing the readsorption of solubilized P by soil colloids. The acidic nature

of the extractant (pH 2.6) also contributes to dissolution of available P from Al, Ca, and Fe-bound forms in most soils.

Uji tanah dnegan metode Bray tidak cocok untuk:1. Tanah-tanah liat yang kejenuhan basanya cukup tinggi,2. Tanah-tanah lempung-liat-berdebu atau yg lebih halus dengan pH tinggi atgau

tanah berkapur (pH > 6.8) atau kejenuhan basanya tinggi,3. Tanah-tanah yang mempunyai kalsium karbonat setara > 7% kejenuhan basa, 4. Tanah-tanah yang kaya kapur ( > 2% CaCO3).



In soils such as these, the acidity of the extracting solution can be neutralized unlessthe ratio of extractant:soil is increased considerably.

Additionally, CaF2, formed from the reaction of soluble Ca+2 in the soil with F- added in the extractant, can react with and immobilize soil P.

Both types of reactions reduce the efficiency of P extraction and result in low soil test P values.

Pengekstraks Bray & Kurtz dapat melarutkan P dari batuan fosfat, sehingga tidak boleh dipakai pada tanah-tanah yang baru diberi bahan-bahan pembenah ini, karena

akan mengakibatkan over-estimate P-tersedia..

Nilai-nilai P ( Bray & Kurtz P-1) sebesar 25 - 30 mg P/kg tanah seringkali dianggap optimum bagi pertumbuhan tanaman, meskipun Holford (1980) melaporkan nilai kritis

yg lebih rendah untuk tanah-tanah yg daya buffernya tinggi.



Peralatan lab:

1. Ayakan No. 10 (diameter lubang 2 mm)2. Standard 1 g and 2 g stainless steel soil scoops3. Automatic extractant dispenser, 25 mL capacity4. Extraction vessels, such as 50 mL Erlenmeyer flasks, and filter funnels (9 and 11

cm) and racks5. Rotating or reciprocating shaker with a capability of 200 excursions per minute

(epm)6. Whatman No. 42 or No. 2 (or equivalent) filter paper, 9 to 11 cm. (Acid resistant

filter paper may be needed if using an automated method for determining P concentration by intensity of color. Bits of filter paper may cause an obstruction in the injection valves.)



Reagen = Pereaksi:

Bray and Kurtz P-1 Extracting Solution (0.025 M HCl in 0.03 M NH4F):

Dissolve 11.11 g of reagent-grade ammonium fluoride (NH4F) in about 9 L of distilled water. Add 250 mL of previously

standardized 1M HCl and make to 10 L volume with distilled water.

Dicampur secara merata. pH larutan yg dihasilkan harus pH 2.6 ± 0.05.

Penyesuaian pH dilakukan dnegan menggunakan HCl atau NH4OH.

Simpan dalam polyethylene-carboys hingga saatnya digunakan.



Prosedur kerja :

1. Scoop or weigh 2 g of soil into a 50 mL Erlenmeyer flask, tapping the scoop on the funnel or flask to remove all of the soil from the scoop.

2. Add 20 mL of extracting solution to each flask and shake at 200 or more epm for five minutes at a room temperature at 24 to 27oC

3. If it is necessary to obtain a colorless filtrate, add 1 cm3 (~200 mg) of charcoal (DARCO G60, J. T. Baker, Phillipburg, NJ) to each flask.

4. Menyaring ekstraks dengan Kertas saring Whatman No. 42. Ulangi kembali penyaringan kalau filtratnya belum jernih.

5. Menganalisis P dengan colorimetry atau spectroscopy dengan menggunakan larutan blanko dan standar yang disiapkan dalam larutan pengekstraks Bray P-1.



Perhitungan:

P yg terekstraks dnegan metode Bray & Kurtz P-1 dihitung :

P-terekstraks Bray & Kurtz P – 1 (mg P/kg tanah ) =(CP x [0.020 L ekstraks] ) / 0.002 kg tanah

dimana: CP = Konsentrasi P dalam ekstraks Bray & Kurtz P-1, mg/L .


References:1. Bray R.H., and L.T. Kurtz. 1945. Determination of total, organic and available forms of phosphorus in soils. Soil

Sci. 59:39-45.2. Frank, K.D. Beegle, and J. Denning. 1998. Phosphorus. p. 21-30. In J. R. Brown (ed.) Recommended Chemical

Soil Test Procedures for the North Central Region. North Central Reg. Res. Publ. No. 221 (revised).3. Holford, I.C.R. 1980. Greenhouse evaluation of four phosphorus soil tests in relation to phosphate buffering and

labile phosphate in soils. Soil Sci. Soc. Am. J. 44:555-559.

Soil Test Phosphorus: Olsen PJ. Thomas Sims, University of Delaware

The “Olsen P” or sodium bicarbonate soil test phosphorus (P) method was developedby Sterling R. Olsen and co-workers in 1954 (Olsen et al., 1954) to predict crop

response to fertilizer P inputs on calcareous soils. It is primarily used in the North Central and western United States.

Metode ekstraksi P-Olsen cocok untuk tanah-tanah berkapur, terutama yang mempunyai > 2% calcium carbonate, tetapi juga cukup efektif untuk tanah-tanah

masam (Fixen and Grove, 1990).

The method is based on the use of the HCO3-, CO3-3 and OH- in the pH 8.5, 0.5M NaHCO3 solution to decrease the solution concentrations of soluble Ca2 by

precipitation as CaCO3 and soluble Al3+ and Fe+3 by formation of Al and Fe oxyhydroxides, thus increasing P solubility.

Peningkatan muatan negatif permukaan dan/ atau penurunan jumlah tapak sorpsi pada permukaan oksida Fe dan Al pada kondisi pH tinggi juga memicu desorpsi P-

tersedia ke dalam larutan.



Nilai P-Olsen sebesar 10 mg P/kg umumnya dianggap optimum bagi pertumbuhan tanaman.

This is lower than the critical values used for the Bray and Kurtz P-1, Mehlich 1 and Mehlich 3 soil tests because the Olsen extractant removes

less P from most soils than these acidic extractants.

Kuo (1996) stated that proper interpretation of Olsen P results for soils with diverse properties requires some information on soil P sorption

capacity.

Menurut Schoenau dan Karamanos (1993), harus hati-hati menggunakan uji P-olsen ini untuk membandingkan ketersediaan P dalam tanah-tanah

yg beragam kimiawi P nya.



Peralatan Lab:

1. Ayakan No. 10 (diameter lubang 2 mm)2. Standard 1 g and 2 g stainless steel soil scoops3. Automatic extractant dispenser, 25 mL capacity4. Extraction vessels, such as 50 mL Erlenmeyer flasks, and filter funnels (9 and 11

cm) and racks5. Rotating or reciprocating shaker with a capability of 200 excursions per minute

(epm)6. Whatman No. 42 or No. 2 (or equivalent) filter paper, 9 to 11 cm. (Acid resistant

filter paper may be needed if using an automated method for determining P concentration by intensity of color. Bits of filter paper may cause an obstruction in the injection valves.)



Pereaksi - Reagen:

Olsen P Extracting Solution (0.5M NaHCO3, pH 8.5): Dissolve 420 g commercial- grade sodium bicarbonate (NaHCO3) in distilled water and

make to a final volume of 10 L.

Note that a magnetic stirrer or electric mixer is needed to dissolve the NaHCO3. Adjust extracting solution pH to 8.5 with 50% sodium

hydroxide.



Prosedur:

1. Scoop or weigh 1 g of soil into a 50 mL Erlenmeyer flask, tapping the scoop on the funnel or flask to remove all of the soil from the scoop.

2. Add 20 mL of extracting solution to each flask and shake at 200 or more epm for 30 minutes at a room temperature at 24 to 270C


4. Filter extracts through Whatman No. 42 filter paper or through a similar grade of paper. Refilter if extracts are not clear.

5. Analyze for P by colorimetry or inductively coupled plasma emission spectroscopy using a blank and standards prepared in the Olsen P extracting solution.



Perhitungan:

P terekstraks Olsen (mg P/kg tanah) =[Konsentrasi P dalam ekstraks Olsen, mg/L ] x [ 0.020 L ekstrak ÷ 0.001

kg tanah]


References:

1. Fixen, P.E. and J.H. Grove. 1990. Testing soils for phosphorus. p. 141-180. In R.L. Westerman (ed.) Soil Testing and Plant Analysis. SSSA, Madison, WI.

2. Kuo, S. 1996. Phosphorus. p. 869-919. In D.L. Sparks. (ed.). Methods of Soil Analysis: Part 3- Chemical Methods. SSSA, Madison, WI.

3. Olsen, S.R., C.V. Cole, F.S. Watanabe, and L.A. Dean. 1954. Estimation of available phosphorus in soils by extraction with sodium bicarbonate. USDA Circular 939. U.S. Government Printing Office, Washington D.C.

4. Schoenau, J.J. and R.E. Karamanos. 1993. Sodium bicarbonate extractable P, K, and N. p. 51-58. In M. R. Carter (ed.) Soil Sampling and Methods of Analysis. Can. Soc. Soil Sci., Ottawa, Ontario.

Soil Test Phosphorus: Mehlich 1J. Thomas Sims, University of Delaware

The Mehlich 1 soil test for phosphorus (P), also known as the dilute double acid or North Carolina extractant, was developed in the early 1950s by Mehlich and his coworkers (Mehlich, 1953; Nelson et al. 1953). In the United States the Mehlich 1 procedure is primarily used in the southeastern and mid-Atlantic states as a multi-element extractant for P, K, Ca, Mg, Cu, Fe, Mn,

and Zn. The Mehlich 1 extracts P from aluminum, iron, and calcium phosphates and is best suited to acid soils (pH < 6.5) with low cation exchange capacities (< 10 cmol/kg) and organic matter

contents (< 5%). Kuo (1996) reported that the Mehlich 1 soil test was unreliable for calcareous or alkaline soils

because it extracts large amounts of nonlabile P in soils with pH > 6.5, soils that have been recently amended with rock phosphate, and soils with high cation exchange capacity (CEC) or

high base saturation.

Dalam tanah-tanah seperti ini, kemasmaan larutan Mehlich-1 dinetralisir, sehingga mengurangi kemampuannya mengekstraks P . Penurunan efisiensi ekstraksi P juga

dapat disebabkan oleh liat dan oksida hidrous aluminum dan besi (Nelson et al., 1953; Lins & Cox, 1989).



Nilai P Mehlich-1 sebesar 20 - 25 mg P/kg tanah untuk uji Mehlich-1 umumnya dianggap optimum bagi pertumbuhan tanaman, meskipun nilai ini beragam di antara tipe-tipe tanah dan sistem pertanaman.

For instance, Kamprath and Watson (1980) stated a Mehlich-1 P of 20 to 25 mg P/kg soil is adequate for plants grown in sandy soils but only 10 mg P/kg soil is required for fine-textured soils, a point supported by the

work of Lins and Cox (1989).



Peralatan Lab:

1. No. 10 (2 mm opening) sieve2. Automatic extractant dispenser, 25 mL capacity (If preferred,

pipettes are acceptable.)3. Standard 5 cm3 and 1 cm3 stainless steel soil scoops4. Extraction vessels, such as 50 mL Erlenmeyer flasks, and filter

funnels (9 and 11 cm) and racks5. Reciprocating or rotary shaker, capable of at least 180 epm

(excursions per minute)6. Whatman No. 42 or No. 2 (or equivalent) filter paper, 9 to 11 cm.

(Acid resistant filter paper may be needed if using an automated method for determining P concentration by intensity of color. Bits of filter paper may cause an obstruction in the injection valves.)



Pereaksi - Reagents:

Mehlich 1 Extracting Solution (0.0125 M H2SO4 + 0.05 M HCl). Also referred to as dilute double acid or the North Carolina Extractant. Using a graduated cylinder, add 167 mL of concentrated HCl (12M) and 28 mL

of concentrated H2SO4 (18M) to ~35 L of deionized water in a large polypropylene carboy.

Buatlah volume akhir 40 L dengan menambahkan air bebas ion. Aduklah dnegan memasukkan gelembung udara ke dalam larutan 3 jam.



Prosedur:

1. Timbang 5.0 g (atau ambil 4 cm3) sampel tanah ayakan (< 2 mm), kering udara dan masukkan ke dalam labu ekstraksi 50 mL.


3. Add 20 mL of the Mehlich 1 extracting solution and shake for five minutes on a reciprocating shaker set at a minimum of 180 epm at a room temperature at 24 to 27oC.

4. Filter through a medium-porosity filter paper (Whatman No. 2 or equivalent).5. Analyze for P by colorimetry or inductively coupled plasma emission spectroscopy using a

blank and standards prepared in the Mehlich 1 extracting solution.

PERHITUNGAN:

P terekstraks Mehlich -1 (mg P/kg tanah) =[Konsentrasi P dalam ekstraks Mehlich -1, mg/L ] x [ 0.020 L ekstrak ÷ 0.005 kg

tanah]



References:

1. Kamprath, E.J. and M.E. Watson. 1980. Conventional soil and tissue tests for assessing the phosphorus status of soils. p. 433-469. In F. E. Khasawneh et al. (ed.) The role of phosphorus in agriculture. ASA, CSSA, and SSSA, Madison, WI.

2. Kuo, S. 1996. Phosphorus. p. 869-919. In D. L. Sparks. (ed.) Methods of Soil Analysis: Part 3- Chemical Methods. SSSA, Madison, WI.

3. Lins, I.D.G. and F.R. Cox. 1989. Effects of extractant and selected soil properties on predicting the optimum phosphorus fertilizer rate for growing soybeans under field conditions. Commun. Soil Sci. Plant Anal. 20:310-333.

4. Mehlich, A. 1953. Determination of P, Ca, Mg, K, Na, and NH4. North Carolina Soil Test Division (Mimeo). Raleigh, NC.

5. Nelson, W. L., A. Mehlich, and E. Winters. 1953. The development, evaluation, and use of soil tests for phosphorus availability. Agronomy 4:153-158.


Soil Test Phosphorus: A Phosphorus Sorption IndexJ. Thomas Sims, University of Delaware

Kapasitas sorpsi P suatu tanah dapat ditentukan dengan eksperimen “batch equilibrium” yg dipakai untuk menghasilkan isotherm sorpsi.

These isotherms are plots of the amount of P adsorbed from several solutions of known initial concentration vs. the P concentration at

equilibrium for each solution. For example, Nair et al., (1984) proposed, based on an interlaboratory comparison study, a standard approach to

construct P sorption isotherms, using a soil:solution ratio of 1:25 (w:v), six initial P concentrations (as KH2PO4 in a 0.01M CaCl2 matrix), and a

24 h equilibration period Hasil-hasil dari sorpsi isothermik ini dapat dipakai untuk menghitung maksimum P-sorpsi dan energi pengikat P untuk tanah-tanah dengan beragam sifat dan/atau dipengaruhi oleh teknologi bubidaya, seperti

rotasi tanaman, olah tanah dan aplikasi rabuk organik.



Bache and Williams (1971) developed a “P Sorption Index” (PSI) that could rapidly determine soil P sorption capacity. They evaluated 12 approaches and found that a PSI

derived from a single-point isotherm (P sorbed from a single solution containing 50 μmol P/g soil) was easy to use and well correlated with the P sorption capacity of 42

acid and calcareous soils from Scotland (r=0.97***).

Other researchers have used the PSI, or modified versions, and shown it to be well correlated with soil P sorption capacity determined from complete sorption isotherms

for soils of widely varying chemical and physical properties (Mozaffari and Sims, 1994; Sharpley et al., 1984; Simard et al., 1994).

Dalam banyak kasus peneliti ini telah mempertahankan rasio orisinil P yg ditambahkan ke tanah (1.5 g/kg), tetapi hanya sedikit mengubah rasio tanah:larutan,

elektrolitnya, dan /atau waktu kocok nya.

Modifikasi ini tidak mempengaruhi korelasi antara kapasitas sorpsi P yg diestimasi dari PSI dengan yang ditentukan oleh sorpsi isothermik.



Peralatan Lab:1. Centrifuge dan tabung centrifuge poli-etilen 50 mL.2. Pengocok (end-over-end shaker preferred to ensure thorough mixing

of soil and sorption solution).3. Peralatan filtrasi Millipore (0.45-μm pore size filters) dan labu-labu

vakum.4. 50 mL screw-top test tubes.

Reagen:

Phosphorus Sorption Solution (75 mg P/L): Dissolve 0.3295 g of monobasic potassium phosphate (KH2PO4) in 1 L of deionized H2O. Store in refrigerator until use.



Prosedur:

1. Timbanglah 1.00 g sampel tanah kering udara, lolos ayakan (2 mm) ke dalam tabung sentrifuge 50 mL.

2. Tambahkan 20 mL larutan sorpsi 75 mg P/L ke dalam tabung sentrifuge. (Note: This provides a ratio of 1.5 g P /kg soil). Add two drops of toluene or chloroform to inhibit microbial activity.

3. Place the tubes in the end-over-end shaker and shake for 18 h at 25±2oC.4. Centrifuge the samples at 2000 rpm for 30 minutes.5. Using the Millipore filtration apparatus, 0.45-μm filters, and large vacuum flasks,

filter the centrifugate into 50 mL screw-top test tubes within the flask.6. Measure P concentration in the centrifugate colorimetrically or by inductively

coupled plasma emission spectroscopy (ICP-AES).



Perhitungan :The PSI has usually been calculated as follows, although some studies

have shown that expressing PSI directly in mg/kg is acceptable.

PSI (L kg-1) = X / Log C

dimana:

X = P sorbed (mgP/kg) = (75mg P/L – Pf) x (0.020 L) ---------------------------------- (0.001kg soil)C = Konsentrasi P pd kesetimbangan (mg/L),Pf = Konsnetrasi akhir P setelah kesetimbangan 18 jam (mg/L).



References:

1. Bache, B.W., and E.G. Williams. 1971. A phosphate sorption index for soils. J. Soil Sci. 22:289-301.

2. Mozaffari, P.M., and J.T. Sims. 1994. Phosphorus availability and sorption in an Atlantic Coastal Plain watershed dominated by intensive, animal-based agriculture. Soil Sci. 157:97-107.

3. Nair, P.S., T.J. Logan, A.N. Sharpley, L.E. Sommers, M.A. Tabatabai, and T.L. Yuan. 1984. Interlaboratory comparison of a standardized phosphorus adsorption procedure. J. Environ. Qual. 13:591-595.

4. Sharpley, A.N., S.J. Smith, B.A. Stewart, and A.C. Mathers. 1984. Forms of phosphorus in soils receiving cattle feedlot waste. J. Environ. Qual. 13:211-215.

5. Simard, R.R., D. Cluis, G. Gangbazo, and A. Pesant. 1994. Phosphorus sorption and desorption indices for soils. Commun. Soil Sci. Plant Anal. 25:1483-1494.


Determination of Water- and/or Dilute Salt-Extractable PhosphorusM.L. Self-Davis, University of Arkansas

P.A. Moore, Jr., USDA-ARS, Fayetteville, ARB.C. Joern, Purdue University

Many methods exist to determine the various forms of soil phosphorus (P). Early interests in examining soil P were primarily based on determining the quantity of

supplemental P needed to adequately meet the needs of crops.

The method for using distilled water as an extractant to determine P needs of plants was examined in a paper by Luscombe et al. (1979). They found a good correlation between

the concentration of water-extractable P and dry matter yield responses in ryegrass.

One criticism of various other extractants is that they are either more acid or alkaline than the soil solution. Therefore, a portion of P extracted is actually of low availability.

For example, extractants such as Mehlich 3, which contain strong acids, would be expected to dissolve calcium phosphates. Also, due to the specific chemical nature of

many extractants, their use is limited to specific soil types. Using distilled water or 0.01 MCaCl2 overcomes these criticisms (Pote et al., 1995).




Peralatan :1. Shaker (reciprocating or end-over-end).2. Centrifuge.3. Centrifuge tubes (40 mL).4. Filtration apparatus (0.45 μm pore diameter membrane filter, or Whatman No. 42).5. Spectrophotometer with infrared phototube for use at 880 nm.6. Acid washed glassware and plastic bottles: graduated cylinders (5 mL to 100 mL),

volumetric flasks (100 mL, 500 mL, and 1000 mL), storage bottles, pipets, dropper bottles, and test tubes or flasks for reading sample absorbance.

Reagent:7. Asam pekat hydrochloric acid (HCl).8. Reagents used for ascorbic acid technique for P determination, Murphy and Riley

(1962).9. Larutan M calcium chloride (CaCl2).10. Chloroform.




Prosedur Ekstraksi - Air bebas ion:

Timbanglah contoh tanah 2 g (dried in a forced-draft oven at 60°C for 48 hours, sieved through a 2-mm mesh sieve) ke dalam tabung sentrifuge 40 mL. Tambahkan 20 mL

air destilasi dan kocok selama satu jam. Centrifuge at 6,000 rpm for 10 minutes. Filter the solution through a 0.45 μm

membrane filter. Acidify to pH 2.0 with HCl to prevent precipitation of phosphate compounds (approximately 2 days of concentrated HC1). Freeze the sample if it is not

going to be analyzed that day.

Previous articles have noted that hydrolysis of condensed phosphates can occur when the solution is acidified (Lee et al., 1965). Also, at this pH level, there is the possibility

of flocculation of organics.However, it is vital to ensure that the P remains in solution, therefore, we consider the

negative effects of acidification minimal.




Prosedur Ekstraksi -- 0.01M CaCl2:

Weigh out 1 g of dry soil into a 40 mL centrifuge tube. Add 25 mL of 0.01 M CaCl2 (you can add 2 drops of chloroform to inhibit microbial

growth if desired) and shake for one hour on a reciprocating shaker. Centrifuge at 4000 rpm for 10 minutes.

Larutan disaring dnegan kertas saring Whatman No. 42.




ANALISIS:For determining water or dilute salt extractable P in soil, any

spectrophotometer with an infrared phototube for use at 660 or 882 nm can be used. Also, samples can be analyzed by inductively coupled

plasma-atomic emission spectrometry (ICP-AES), which will measure total dissolved P.

PERHITUNGAN:P terekstraks air atau larutan garam encer (mg P/kg tanah) =

[Konsentrasi P dalam ekstraks, mg/L] x [Volume pengekstraks, L ÷ masa tanah, kg]




References:1. Lee, G.R., N.L. Clesceri, and G.P. Fitzgerald. 1965. Studies on the analysis of phosphates in algal

cultures. Internat. J. Air Water Poll. 9:715-722.2. Luscombe, P.C., J.K. Syers, and P.E.H. Gregg. 1979. Water extraction as a soil testing procedure for

phosphate. Commun. Soil Sci. Plant Anal. 10:1361-1369. 3. Murphy, J., and J.P. Riley. 1962. A modified single solution method for the determination of phosphate

in natural waters. Anal. Chem. Acta 27:31-36.4. Olsen, S.R., and L.E. Sommers. 1982. Phosphorus. P. 403-430 In A.L. Page et al. (ed.) Methods of soil

analysis. Part 2. 2nd ed. Agronomy Monogr. 9. ASA and SSSA, Madison, WI.5. Olsen, S.R., and F.S. Watanabe. 1970. Diffusive supply of phosphorus in relation to soil textural

variations. Soil Sci. 110:318-327.6. Pote, D.H., T.C. Daniel, P.A. Moore, Jr., A.N. Sharpley, D.R. Edwards, and D.J. Nichols. 1995.

Phosphorus: relating soil tests to runoff concentrations across five soil series. Agronomy Abstracts, p. 294, Am. Soc. Agron., Madison, WI.

7. Pote, D.H., T.C. Daniel, A.N. Sharpley, P.A. Moore, Jr., D.R. Edwards, and D.J. Nichols. 1996. Relating extractable soil phosphorus to phosphorus losses in runoff. Soil Sci. Soc. Am J. 60:855-59.

8. Sharpley, A.N. 1995. Dependence of runoff phosphorus on extractable soil phosphorus. J. Environ. Qual. 24:920-926.

9. Soltanpour, P.N., F. Adams, and A.C. Bennett. 1974. Soil phosphorus availability as measured by displaced soil solutions, calcium chloride extracts, dilute-acid extracts, and labile phosphorus. Soil Sci. Soc. Am. Proc. 38:225-228.


Bioavailable Phosphorus in SoilAndrew Sharpley, USDA-ARS, University Park, PA

Biologically available P (BAP) didefinisikan sebagai “….. Jumlah P-anorganik , yg dapat digunakan oleh populasi algae yg defisien P selama periode 24 jam atau lebih “

(Sonzogni et al., 1982).

Jumlah P dalam tanah, sedimen, dan air yang secara potensial tersedia bagi serapan algae (bioavailable P) dapat dikuantifikasikan dengan “algal assays”, yg memerlukan

waktu inkubasi hingga 100 hari (Miller et al., 1978). Thus, more rapid chemical extractions, such as those using NaOH (Butkus, et al., 1988; Dorich et al., 1980), NH4F

(Porcella et al., 1970), ion exchange resin (Huettl et al., 1979) and citrate-dithionitebicarbonate (Logan et al., 1979), have been used routinely to estimate

bioavailable P.

The weaker extractants (NH4F and NaOH) and short-term resin extractions may represent P that could be utilized by algae in the photic zone of lakes under aerobic conditions. In contrast, the more severe extractants (citrate-dithionite-bicarbonate)

represent P that may become bioavailable under the reducing conditions found in the anoxic hypolimnion of stratified lakes.



Sharpley et al. (1991) showed that when using a wide solution:soil ratio (500:1), 0.1 M NaOH extractable P (NaOH-P) was closely related to the growth of several algal

species. However, the complexity of algal assay and chemical extraction methods often limits their use by soil testing laboratories.

For example, long assay incubation (7 to 100 d) and chemical extraction times (> 16 hr), as well as large solution volumes (> 500 mL) are particularly inconvenient.

As the amount of P extracted depends on ionic strength, cationic species, pH, and volume of the extractant used (Hope and Syers, 1976; Sharpley et al., 1981), these

limitations will be difficult to overcome.

Pertanyaan juga telah muncul tentang validitas hubungan antara bentuk atau ketersediaan P ekstraks larutan kimia dengan bio-availabilitas P dalam lingkungan

akuatik.

Pendekatan P-sink telah dikembangkan untuk estimasi BAP dalam tganah, sedimen, dan air.



P-Sink Approaches:The concept of exposing the soil to a P-sink has merit toward the goal of assessing soil,

sediment, and water BAP (i.e., available to plants and algae) for both agronomic and environmental goals.

Presumably, this would allow only P that was able to respond to such a sink to be measured, which is analogous to a root acting as a sink in the soil or to the

concentration gradient that exists when a small quantity of sediment is placed in a large volume of water. The analogy of a root is not entirely accurate because root exudates

and mycorrhizae fungi can alter P availability in the rhizosphere such that the root does not behave as a pure sink. Still, P-sinks are likely the closest manifestation of the root

environment that are available. Some authors assume that the sink maintains extremely low P concentrations in the aqueous media employed and can be considered an "infinite P-sink" in the sense that P release by the soil is clearly the rate-limiting step (Sibbesen,

1978; van der Zee et al., 1987; Yli-Halla, 1990).

For anion-exchange resins used at low resin:soil ratios, this relationship cannot be assumed (Barrow and Shaw, 1977; Pierzynski, 1991) and is not necessary for the

assessment of bioavailable P.



Iron-oxide-Impregnated Paper

Another P sink that has received attention is Fe-oxide impregnated filter paper, whichhas successfully estimated plant available P in a wide range of soils and management

systems (Menon et al., 1989; 1990, Sharpley, 1991).

Also, Sharpley (1993) observed that the Fe-oxide strip P content of runoff was closely related to the growth of several algal species incubated for 29-d with runoff as the sole source of P. As the resin membranes and Fe-oxide strips act as a P sink, they simulate P removal from soil or sediment-water samples by plant roots and algae. Thus, they have

a stronger theoretical justification for use over chemical extractants to estimate bioavailable P. These methods have potential use as environmental soil P tests to

identify soils liable to enrich runoff with sufficient P to accelerate eutrophication.

The Fe-oxide impregnanted filter paper procedure was described in the section by Chardon (2000) in this bulletin and will not be described

further here.



RESIN PENUKAR-ANION

The use of anion-exchange resins is the most common P-sink approach for assessing available inorganic P in soils.

The procedure typically involves the use of chloridesaturated resin at a 1:1 resin-to-soil ratio in 10 to 100 mL of water or weak electrolyte for 16

to 24 h (Amer et al., 1955; Olsen and Sommers, 1982).

Korelasi antara respon tanaman dan P-terekstraks resin ternyata sebanding atau superior dibandingkan dengan korelasi metode-metode

ekstraksi kimia (Fixen dan Grove, 1990).



Ion-exchange Resin-Impregnated Membranes

A similar approach using ion-exchange resin impregnated membranes has been investigated by several researchers (Abrams and Jarrell, 1992; Qian et al., 1992: Saggar et al., 1992).

Impregnation of the resin onto a plastic membrane facilitates separation of the resin beads from the soil and may eliminate the soil grinding step. Also, an extraction time as short as 15 min can be used without reducing the accuracy of predicted P availability for a wide range of soils (Qian et al., 1992). In pot studies, the resin membranes have provided a better index of P availability

than conventional chemical extraction methods for canola (Qian et al., 1992) and ryegrass (Saggar et al., 1992). It is likely that the utility of the resin membranes will make the use of loose

resin obsolete. Ion exchange membranes have the potential to estimate P availability in aquatic as well as soil

environments. Edwards et al. (1993) used ion exchange membranes to obtain in-situ estimates of the chemical composition of river water for two Scottish watersheds.

It was suggested that direct multi-element analysis by X-ray fluorescence of ions retained on the membranes removes the need for sample storage or filtration, both of which can be sources of

potential contamination and error. Thus, the membranes can provide useful information in addition to that obtained by conventional sampling (Edwards et al., 1993).



SAMPLING TANAH:

Soil sampling protocol for environmental concerns should be re-evaluated since the primary mechanism for P transport from most agricultural soils is by surface runoff and erosion. Although most samples submitted to soil testing laboratories are obtained from 0 to 20 cm, the zone of interaction of runoff waters with most

soils is normally less than 5 cm. Consequently, environmental soil sampling should reflect this shallower depth

of soil influencing runoff P. Hence, environmental soil samples should, in general, be taken from no deeper than 5 cm. This protocol is compatible with sampling of no-till fields, currently recommended by extension specialists in several states, where the traditional 0-to 20-cm depth is split into two or three

increments. Pada tanah-tanah yang rentan terhadap kehilangan P melalui runoff, the surface

increment could be analyzed for environmental interpretation and all increments integrated for agronomic interpretations.



PERALATAN:

The following equipment is needed to conduct BAP extraction of soil and analysis for P:

1. Membran Resin, penukar anion.2. End-over-end shaker - used to equilibrate sample and sink3. Labu Volumetrik – biasanya volume 25 atau 50 mL4. Pipets untuk sampel aliquot dan reagen warna5. Spectrophotometer untuk menentukan konsentrasi P dalam reagen

yg menjadi berwarna kalau ketemu sampel.



Reagents:

Membran Resin

Hydrochloric acid to extract P from the membranes - 1.0 M HCl (166 mL concentrated HCl in 2 L)

Murphy and Riley Molybdenum Blue Color Reagent



Resin Strip Procedure:1. Anion exchange resin sheets are cut into 2 x 2 cm squares and are stored in propylene glycol.

Wash the resin squares in distilled water to remove all the propylene glycol. If not already saturated with an anion, saturation with C1- , HCO3- or acetate may be necessary. They are now ready for use.

2. Phosphorus is extracted from soil or sediment by shaking a 1-g sample and one resin membrane square in 40 mL of deionized distilled water end-over-end for 16 hours at 25o C.

3. Remove the resin membrane square and wash thoroughly with distilled water until all soil particles are removed.

4. The BAP content of runoff can also determined by shaking 50 mL of an unfiltered runoff sample with one resin membrane square for 16 hours. Smaller runoff sample volumes should be used if P concentrations are expected to be high (>1 or 2 mg/L) and made up to 50 mL with distilled water.

5. Phosphorus retained on the resin membrane square is removed by shaking the square end-over-end with 40 mL of 1 M HCl for 4 hours. Remove square and rinse with distilled water. Retain the HCl desorption solution for analysis. Repeat this step. Do not mix the first and second desorption solutions.

6. Mengukur konsentrasi P dua macam larutan secara terpisah. Jumlah total desorpsi P dari membran resin berbentuk kuadrat adalah jumlah dari dua larutan itu.



Perhitungan:P-terekstraks Resin (mg P/kg) = [Konsentrasi P dalam 1 MHCl, mg/L] x [0.04 L ÷ 0.001 kg]

Resin BAP dalam runoff (mg P/L) = [konsentrasi P dalam 1 M HC1, mg/L] x [0.04L ÷ volume runoff, L]

References:1. Abrams, M.M., and W.M. Jarrell. 1992. Bioavailability index for phosphorus using nonexchange resin impregnated

membranes. Soil Sci. Soc. Am. J. 56:1532-1537.2. Amer, F., D.R. Bouldin, C.A. Black, and F.R. Duke. 1955. Characterization of soil phosphorus by anion exchange resin

and adsorption by P-32 equilibration. Plant Soil 6:391-408.3. Barrow, N.J., and T.C. Shaw. 1977. Factors affecting the amount of phosphate extracted from soil by anion exchange

resin. Geoderma 18:309-323.4. Butkus, S.R., E.B. Welch, R.R. Horner, and D.E. Spyridakis. 1988. Lake response modeling using biologically available

phosphorus. J. Water Pollut. Cont. Fed. 60:1663-1669.5. Chardon, W.J. 2000. Phosphorus extraction with iron oxide-impregnated filter paper (P; test). In G.M. Pierzynski (ed.),

Sediments, Residuals, and Waters. Southern Cooperative Series Bulletin No. 396, p. 27-30.6. Dorich, R.A., D.W. Nelson, and L.E. Sommers. 1980. Algal availability of sediment phosphorus in drainage water of

the Black Creek watershed. J. Environ. Qual. 9:557- 563.7. Edwards, T., B. Ferrier, and R. Harriman. 1993. Preliminary investigation on the use of ion-exchange resins for

monitoring river water composition. Sci. of Total Environ. 135:27-36.


Total Phosphorous in SoilM.R. Bender and C.W. Wood, Auburn University

There have been many methods developed to extract and analyze total phosphorus (P)in soil (Bray and Kurtz, 1945; Muir, 1952; Jackson, 1958; Syers et al., 1968; Sommers

and Nelson, 1972; Dick and Tabatabai, 1977; Olsen and Sommers, 1982; Bowman,1988).

Two of the more commonly used and most recognizable methods of P extractionare sodium carbonate (Na2CO3) fusion and acid digestion. Of these methods, Na2CO3

fusion is thought to give more reliable results (Syers et al., 1967; Syers et al., 1968;Sherrell and Saunders, 1966; Sommers and Nelson, 1972). Underestimation of total P by acid digestion is thought to be due to inability of these methods to extract P from

apatite inclusions (Syers et al., 1967).

Kemampuan “acid digestion” untuk mengekstraks P dari inklusi terganutng pada asam atau kombinasi asam yang dipakai.

Menurut Syers et al. (1967) , efektivitas ekstraksi umumnya mengikuti urutan : Fusi > HF digestion > HClO4 digestion > N H2SO4 > ignition.



In recent years, more rapid methods for determining total P in soils have beendeveloped (Sommers and Nelson, 1972; Dick and Tabatabai, 1977; Bowman, 1988).

Methods developed by Sommers and Nelson (1972) and Bowman (1988) are variationsof standard HClO4 digestion methods. These methods were shown to give a similar

degree of underestimation of total P as standard HClO4 digestion methods.

Dick dan Tabatabai (1977) mengusulkan metode oksidasi alkaline menggunakan sodium hypobromite (NaOBr).

Metode ini ternyata menghasilkan 1% lebih tinggi dibandingkan dnegan hasil dari metode HClO4 digestion. Akan tetapi, metode ini masih underestimate P-total sebesar 4% kalau dibandingkan dnegan

hasil metode fusi Na2CO3.



Fusion Method (Olsen and Sommers (1982)):

Reagents1. Anhydrous sodium carbonate (Na2CO3)2. Larutan 4.5 M H2SO43. Larutan 1 M H2SO44. Ammonium paramolybdate [(NH4)6Mo7O24.H2O]. Prepare by dissolving 9.6 g of

(NH4)6Mo7O24. 4H2O in distilled water under heat. After solution has cooled, dilute solution volume to 1 L with distilled water.

5. Larutan 2 M H2SO46. Ascorbic acid. Prepare by dissolving 10 g of ascorbic acid in 80 mL of distilled water, and

dilute solution volume to 100 mL with distilled water. Store reagent at 2°C. Make fresh solution when noticeable color develops.

7. Potassium antimony tartrate (KSbO.C4H4O6). Prepare by dissolving 0.667 g of KSbO.C4H4O6 in 250 mL of distilled water.

8. Mixed reagent. Mix 1:1 ratio of ascorbic acid and antimony reagents prior to use.

Siapkan larutan segar sebanyak yang diperlukan.



Prosedur:Place a mixture of 1.0 g of finely ground (100 mesh), air-dried soil and 4-5 g of Na2CO3 in a Pt crucible. For soils high in Fe, use 0.5 g of soil. Place 1 g of Na2CO3 on top of the mixture. Drive off moisture from mixture by gently heating with a Meeker burner. Place a lid on the crucible so that approximately one fifth of the crucible remains open. Apply heat with a low flame for 10 min so the mass fuses gently. Adjust heat of Meeker burner to full, and heat mass for 15 to 20 min. To provide an oxidizing environment for this step, lift the lid of the crucible periodically. Do not allow the reduced portion of the flame to come in contact with the crucible. Remove crucible from flame. Rotate crucible as it cools so to deposit the melt thinly onto the walls of the crucible. After the crucible has cooled, gently roll it between your hands to facilitate the removal of the melt. Remove the melt with 30 mL of 4.5 M H2SO4, using care to avoid loss by effervescence. Place crucible and lid in a beaker containing 25 mL of 1 M H2SO4, and heat contents to a boil. Transfer the solution from the beaker and the solution from the melt to a 250 mL volumetric flask. Dilute the solution to volume using distilled water.Allow sediment to settle. Remove an aliquot of clear supernatant solution for total P analysis by the ascorbic acid method. To analyze for total P, transfer aliquots (2 mL) into 50 mL volumetric flasks (for samples containing <150 mg of P). With 1 M Na2CO3, adjust pH of the aliquot to 5 using p-nitrophenol indicator. Add 5 mL of 2 M H2SO4 and 5 mL of ammonium paramolybdate reagent and mix. Add 4 mL of the mixed reagent and mix contents of the flask. Bring to 50 mL volume with distilled water and mix thoroughly. Reduction is completed and maximum color intensity develops in 10 min, and color is stable for 24 hours. The absorption maximum of the blue color formed in the presence of Sb is at 890 nm (Harwood et al., 1969)



KOMENTAR

The method for color development was described by Harwood et al. (1969) and is avariation of the method proposed by Murphy and Riley (1962). By increasing amount of antimony added, Harwood et al. (1969) found that the range of the calibration curve

could be extended. This modification of the Murphy and Riley (1962) method was found to increase the upper limit of the calibration curve from 50 mg P/50ml sample to

150 mg P/50ml sample.It should be noted that presence of arsenic in the form of AsO4 in soil samples gives the same blue color as phosphate. To eliminate this problem, AsO4 can be reduced to

AsO3 using a NaHSO3 solution as described in the following digestion method (Olsen and Sommers, 1982).

PERHITUNGAN

Total P, mg/kg =[Konsentrasi P dalam pengenceran initial 250 mL, mg/L] x [0.25 L ÷ masa tanah, kg]



Digestion Method (Olsen and Sommers (1982)):

Reagents

1. Larutan 60% Perchloric acid (HClO4)2. Ammonium paramolybdate-vanadate. Prepare by dissolving 25 g of

(NH4)6Mo7O24 . 4H2O in 400 mL of distilled water, and by dissolving ammonium metavanadate (NH4VO3) in 300 mL of boiling distilled water. Cool vanadate solution, and add 250 mL of conc. HNO3. Cool NH4VO3-HNO3 solution to room temperature before adding (NH4)6Mo7O24. 4H2O solution. Dilute the mixed solution to 1 L with distilled water.

3. Standard phosphate solution. Prepare by dissolving 0.4393 g of oven-dried potassium dihydrogen phosphate (KH2PO4) in distilled water. Dilute solution to 1 L with distilled water. Standard solution contains 100 mg P/L.

4. Sodium hydrogen sulfite (NaHSO3). Prepare by dissolving 5.2 g of reagent grade NaHSO3 in 100 mL of 0.5 M H2SO4.

5. Persiapkan reagen setiap mingguan.



Prosedur Kerja:

In a 250 mL volumetric or Erlenmeyer flask, mix 2.0 g of finely ground soil (<0.5 mm) with 30 mL of 60% HClO4. Digest the soil and acid mixture at a few degrees below the boiling point on a hot plate in a perchloric hood until the dark color from organic matter disappears. Continue to heat at the boiling temperature for 20 min longer. Heavy white fumes will appear, and the insoluble material will become like white sand. If any black particles stick to the side of the flask, add 1 or 2 mL of HClO4 to wash down the particles. If the sample is high in organic matter it may be necessary to add 20 mL of HNO3 and heat to oxidize organic matter before adding HClO4. Total digestion time is approximately 40 min. Cool the mixture before bringing the volume up to 250 mL with distilled water. Mix the contents of the flask, and then allow sediment to settle.To analyze for total P, transfer aliquots into 50 mL volumetric flasks (for samples containing between 0.05 to 1.0 mg of P). Add 10 mL of the ammonium paramolybdatevanadate reagent, and bring the volume of the flask up to 50 mL using distilled water. The optical density of the sample can be measured after 10 min at wavelengths between 400 to 490 nm. The optical density of a reagent blank should be subtracted from the optical density readings of the samples.To reduce AsO4-3 to AsO3-3, add 5 mL of NaHSO3 solution to the aliquot. Then partially immerse the 50 mL volumetric flasks in a water bath, and digest the solution for 30 min (20 min after temperature reaches 95oC). An alternative procedure is to allow the solution to stand for 4 hours at room temperature.

PERHITUNGAN

Total P, mg/kg =[Konsentrasi P dalam pengenceran initial 250 mL , mg/L] x [0.25 ÷ masa tanah, kg]



Metode Oksidasi Alkaline (Dick and Tabatabai (1977)):

Pereaksi - Reagents1. Sodium hypobromite solution (NaOBr-NaOH). Prepare by slowly adding 3 mL of

bromine (0.5 mL/min) to 100 mL of 2 M NaOH under constant stirring. Prepare reagent immediately prior to use.

2. Larutan 90 % formic acid3. Larutan 2.5 M H2SO44. Ammonium molybdate -Antimony potassium tartrate solution. Prepare by

dissolving 12 g of ammonium molybdate in 250 mL of distilled water, and dissolving 0.2908 g of antimony potassium tartrate in 100 mL of distilled water. Add both solutions to 1 L of 2.5 M sulfuric acid, and dilute volume to 2 L with distilled water. Store reagent in a cool place, in a dark Pyrex glass bottle.

5. Ascorbic acid. Prepare by dissolving 1.056 g of ascorbic acid in 200 mL of ammonium molybdate - antimony reagent. Prepare reagent daily.

6. Standard phosphate solution. Prepare by dissolving 0.2195 g of potassium dihydrogen phosphate (KH2PO4) in distilled water. Dilute solution to 1L with distilled water. Standard solution contains 50 mg P/L.



Prosedur kerja1. Place a 100 to 200 mg sample of finely ground, air-dried soil in a 50 mL boiling

flask.2. Add 3 mL of sodium hypobromite solution to the flask, and swirl flask for a few

seconds to mix contents. Allow flask to stand for 5 min. Swirl flask again and place it in a sand bath adjusted to 260 to 280oC. The sand bath should be situated in a hood. Heat flask until contents evaporate to dryness. Evaporation time is 10 to 15 min. After evaporation, continue to heat for an additional 30 min. Remove flask from sand bath, and allow it to cool for 5 min. Then add 4 mL of distilled water and 1 mL of formic acid. Mix contents before adding 25 mL of 0.5 M H2SO4. Stopper flask and mix contents. Transfer mixture to a 50 mL plastic centrifuge tube and centrifuge sample at 12,000 rpm for 1 min.

3. To analyze for total P, transfer aliquots of 1 to 2 mL into 25 mL volumetric flasks.4. Add 4 mL of ascorbic acid reagent, and bring solution up to volume with distilled

water.5. Stopper flask and mix solution. Allow solution to stand for 30 min for color

development.6. Optical density of sample should be measured at a wavelength of 720 nm.



KOMENTAR

This method does not require neutralization of the 1 to 2 mL of aliquot, however,longer time (30 min) is needed for full color development.

The sodium hypobromite (NaOBr-NaOH) reagent should be prepared just prior to use.The reagent should be made in a fume hood. Formic acid added after the hypobromite

treatment will destroy any residual hypobromite remaining after oxidation of the sample.

PERHITUNGAN

Total P, mg/kg =[konsentrasi P dalam larutan initial asam fosmat /H2SO4, mg/L] x [0.03 L ÷ masa tanah, kg]



References:

1. Bowman, R.A. 1988. A rapid method to determine total phosphorus in soils. Soil Sci. Soc. Am. J. 52:1301-1304.2. Bray, R.H., and L.T. Kurtz. 1945. Determination of total, organic, and available forms of phosphorus is soils. Soil Sci.

59:39-45.3. Dick, W.A., and M.A. Tabatabai. 1977. An alkaline oxidation method for determination of total phosphorus in soils.

Soil Sci. Soc. Am. J. 41:511-514.4. Harwood, J.E., R.A. van Steenderen, and A.L. Kuhn. 1969. A rapid method for orthophosphate analysis at high

concentrations in water. Water Res. 3:417-423.5. Jackson, M.L. 1958. Soil chemical analysis. Prentice-Hall, Inc., Englewood Cliffs, N.J. Muir, J.W. 1952. The

determination of total phosphorus in soil. Analyst 77:313-317.6. Murphy, J., and J.P. Riley. 1962. A modified single solution method for determination of phosphate in natural waters.

Anal. Chim. Acta 27:31-36.7. Olsen, S.R., and L.E. Sommers. 1982. Phosphorus. pp. 403-430. In: A.L. Page. R.H. Miller, and D.R. Keeney (eds.),

Methods of Soil Analysis. 2nd ed. Agronomy Series No.9, Part 2. Soil Science Society of America, Inc., Madison, WI.8. Sherrell, C.G., and W.M.H. Saunders. 1966. An evaluation of methods for the determination of total phosphorus in

soils. N.Z.J. Agric. Res. 9:972-979.9. Sommers, L.E., and D.W. Nelson. 1972. Determination of total phosphorus in soils: a rapid perchloric acid digestion

procedure. Soil Sci. Soc. Amer. Proc. 36:902-904.10. Syers, J.K., J.D.H. Williams, A.S. Campbel, and T.W. Walker. 1967. The significance of apatite inclusions in soil

phosphorous studies. Soil Sci. Soc. Amer. Proc. 31:752-756.11. Syers, J.K., J.D.H. Williams, and T.W. Walker. 1968. The determination of total phosphorus in soils and parent

materials. N.Z.J. Agric. Res. 11:757-762.


TERIMA-KASIH

….. Ayo belajar bersama ……

www.marno.lecture.ub.ac.id

bahan kajian mk. dasar ilmu tanah fosfat tanah

Documents