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Presentasi berjudul: "BAHAN KAJIAN MK. DASAR ILMU TANAH FOSFAT TANAH www.marno.lecture.ub.ac.id."— Transcript presentasi:

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2 BAHAN KAJIAN MK. DASAR ILMU TANAH FOSFAT TANAH

3 diunduh dari: ….. _soil_phosphorus.php SIKLUS P DALAM TANAH PERTANIAN Serapan Tanaman P-organik P- pupuk P- mineralP- larutan P- terserap Pencucian & Runoff sorpsi desorpsi pengendapan pelarutan mineralisasi imobilisasi

4 Problematik Fosfor Jumlah sedikit yang terdapat dalam tanah Ketidak- tersediaan fosfor yg sdh ada dalam tanah Adanya fiksasi fosfor yang menyolok

5 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

6 Senyawa P dalam tanah Senyawa P an-organik 1. Senyawa Kalsium 2. Senyawa besi dan aluminium Senyawa Rumus Kelarutan Fluor-apatit3 Ca3(PO4)2.CaF Karbonato-apatit3 Ca3(PO4)2.CaCO3 Hidroksi-apatit3 Ca3(PO4)2.Ca(OH)2 Oksi-apatit3 Ca3(PO4)2.CaO Trikalsium-fosfatCa3(PO4)2 Dikalsium-fosfatCaHPO4 naik Monokalsium-fosfat Ca(H2PO4)2 Senyawa P-organik: 1. Fitin dan derivatifnya 2. Asam Nukleat 3. Fosfolipida

7 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

8 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

9 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)

10 Senyawa P-anorganik (mengendap) Tanah-tanah masam 8 Fe dan Al fosfat FePO 4 2H 2 O, AlPO 4 2H 2 O Tanah-tanah Alkaline 4 Ca dan Mg fosfat

11  Ca(H 2 PO 4 ) 2  monocalcium phosphate  CaHPO 4  dicalcium phosphate  Ca 3 (PO 4 ) 2  tricalcium phosphate  3Ca 3 (PO 4 ) 2 Ca(OH) 2  hidroksi-apatit  3Ca 3 (PO 4 ) 2 CaCO 3  Apatite karbonat Kelarutan menurun Senyawa P-anorganik pH 6 8

12 Tata-nama anion fosfat H 3 PO 4 = phosphoric acid H 2 PO 4 - = monobasic HPO 4 -2 = dibasic PO 4 -3 = tribasic

13 Fosfat paling tersedia pada kisaran pH Oksida hidrous

14 P-Organik dalam tanah * Sekitar % dari P-total dalam tanah berupa P-organik * Kebanyakan berupa fosfat-inositol, C 6 H 6 (OH) 6 - sekitar % 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.

15 P-Organik (P-tersedia) Siklus : Mekanisme pelepasan lambat H x PO 4 x-3 mineralisasi imobilisasi Fase fosfat padatan (tidak-tersedia)

16 HUBUNGAN SIMBIOSIS : Fungi dan Tumbuhan Infeksi mikorhiza akar, kunci penyerapan fosfat Hifa fungi Mikorhiza Akar tumbuhan

17 Reaksi fosfat pada tanah alkalis pH tinggi P berubah menjadi bentuk sukar larut senyawa-senyawa Ca dan Mg Ca(H 2 PO 4 ) 2 + CaCO 3 + H 2 O  2 CaHPO 4  2H 2 O + CO 2 mudah larut kurang-larut 6 CaHPO 4  2H 2 O + 3 CaCO 3  3 Ca 3 (PO 4 ) CO H 2 O Kurang larut 3 Ca 3 (PO 4 ) 2 + CaCO 3  3Ca 3 (PO 4 ) 2  CaCO 3 sangat tidak larut Masalah sangat serius pada tanah-tanah kapur di daerah iklim kering

18 acid soils alkaline soils soils Dinamika ion fosfat: Protonasi

19 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 - H 2 PO 4 - H2O + HPO 4 = H2O + PO larutan tanah sangat masam sangat alkalin % kepekatan H 3 PO 4 H2PO 4 - HPO 4 = PO pH larutan Paling tersedia bagi tanaman

20 Ketersediaan P-anorganik tanah masam Pengendapan oleh kation Fe, Al, Mn Al 3+ + H 2 PO H 2 O 2H + + Al(OH) 2 H 2 PO 4 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 + H 2 PO 4 - OH - + Al OH larut tdk larut OH larut H 2 PO 4 tdk larut Hidro-oksida Al Pengikatan oleh liat silikat: Kaolinit, Montmorilonit, Illit 1. Reaksi permukaan antara gugusan OH- yang tersembul di permukaan liat dengan anion fosfat 2.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 silikattidak larut

21 Ketersediaan P-anorganik pd pH tinggi Pengendapan oleh kation Ca++ atau CaCO3 H 2 PO Ca ++ Ca 3 (PO 4 ) 2 + 4H + larut tidak larut H 2 PO CaCO 3 Ca 3 (PO 4 ) 2 + 2CO 2 + 2H 2 O larut tidak larut Ca 3 (PO 4 ) 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)

22 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(H 2 PO 4 )2 Tidak larut: CaHPO 4 dan Ca 3 (PO 4 )2

23 Kemampuan tanah menjerap (Daya Jerap) P Tanah Mineral Liat Perlakuan pH Daya Jerap P (*) Latosol - Tanpa kapur PurwokertoHaloisitDengan kapur Latosol-KaolinitTanpa kapur CibodasDengan kapur Podsolik-SmektitTanpa kapur GajrugDengan kapur Podsolik-SmektitTanpa kapur SamarindaKaolinitDengan kapur Grumusol-Smektit, KaolinitTanpa kapur YogjakartaHaloisit Andosol BogorAlofan, HaloisitTanpa kapur Keterangan: (*) setara dengan kg superfosfat 20% P2O5 setiap HLO Pengapuran setara dengan 0.5 SMP Sumber: Djokosudardjo (1982)

24 Pengelolaan P - Tanah Pengendalian P-tersedia dalam tanah: 1. Pengapuran 3. Pengendalian fiksasi P-tanah 2. Penempatan pupuk P-tanah Tersedia Limbah tanaman Pupuk kandang Pupuk buatanMineral tanah BOT TanamanPencucianFiksasiErosi

25 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)

26 P- tanah P-anorganik: 1. Fraksi aktif: Al-P, Fe-P dan Ca-P 2. Fraksi tidak aktif: P-terjerap (P-absorption) P-terselimuti (P-occluded) P-organik 1. Inositol fosfat, Fosfolipid, Asam nukleat, Nukleotida, Gula-fosfat 2. P-organik menyumbang 30-50% dari P-total tanah 3. Senyawa P-organik terdapat dalam humus dan tubuh jasad tanah 4. P-organik dalam tanah berasal dari bahan organik Penambahan bahan organik ke tanah bertujuan: 1. Meningkatkan kandungan bahan organik tanah 2. Sumber unsur hara N,P,K, dan lainnya 3. Meningkatkan KTK tanah 4. Mengurangi jerapan P melalui pembentukan senyawa kompleks dg oksida amorf 5. Meningkatkan dan memperbaiki agregasi tanah & lengas tanah 6. Membentuk khelate dengan unsur hara mikro 7. Detoksifikasi Al 8. Meningkatkan biodiversitas tanah.

27 1. No direct practical importance 2. Sering dipakai sbg “Indeks Pelapukan” 3. P-total topsoil menurun dengan intensitas pelapukan 4. Tanah-tanah tropis mengandung sekitar 200 ppm 5. Ultisol & Alfisol : < 200 ppm P 6. Andepts umumnya ppm P 7. Vertisol umumnya ppm P 8. Entisol & Inceptisols: beragam p-totalnya 9. Oxisols umumnya < 200 ppm P 10. …..

28 1. P-organik = % total P-tanah 2. Oxisols, Ultisols, Alfisols: P-organik = 60-80% P-total 3. C:P rasio dalam tanah = 240: :1 4. N:P rasio dlm tanah = 20:1 -- 9:1 5. 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.

29 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-total 4. Kandungan lignin dan polifenol 5. 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 P 2. Bahan organik dengan kandungan P lebih dari 2500 ppm akan terjadi mineralisasi P dan menurunkan jerapan P-tanah 3.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 air b. 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

30 1. P - ANORGANIK: Fraksi aktif & Fraksi tidak aktif 2. Fraksi aktif : Ca-P, Al-P dan Fe-P 3. Fraksi tdak-aktif : Occluded-P dan Reductant-soluble P 4. 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 anaerobik 6. Transformasi bentuk-bentuk P-tanah dikendalikan pH 7. Ca-P lebih mudah larut dp Fe-P dan Al-P 8. Rezim air sgt berpengaruh thd transformasi P-tanah 9. Kondisi AQUIK ---- Akumulasi Al-P 10. Kondisi USTIK Akumulasi Fe-P

31 Faktor Retensi P dalam tanah TIPE LIAT Tanah-tanah liat lebih banyak meretensi & memfiksasi p- pupuk daripada tanah berpasir Liat silikat tipe 1:1 mempunyai kemampuan lebih besar me-”retensi” P dibanding liat tipe 2:1 Tanah yang kaya liat kaolinitik akan “mengikat” lebih banyak P -pupuk daripada tanah yang kaya liat tipe 2:1 Adanya liat oksida hidrous dari Fe dan Al juga terlibat dalam retensi P-pupuk TIME OF REACTION Semakin lama P-pupuk kontak langsung dengan tanah akan semakin besar jumlah retensi & fiksasi P Hal 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? …………

32 Faktor Retensi P dalam tanah pH TANAH Kisaran pH tanah yg optimum bagi ketersediaan p-tanah adalah Pd 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 TEMPERATUR Tanah 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 ORGANIK Dekomposisi 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 tanaman 2. Penggantian anion fosfat oleh humat 3. Penyelimutan partikel sesquioksida oleh humus, membentuk selimut protektif sehingga mereduksi kapasitas fiksasi fosfat …………………………..

33 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 fosfat Anion-anion organik ini juga mampu melepaskan fosfat yang difiksasi oleh Fe dan Al Anion-anion yang efektif menggantikan fosfat tsb adalah sitrat, oksalat, tartrat, malat, dan malonat. STATUS FOSFOR dalam TANAH Tingkat 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 besar Oleh karenanya tanah-tanah yag dipupuk fosfat dosis tinggi selama bertahun- tahun kemungkinan akan: 1. Mereduksi dosis pupuk P saat ini 2. Menggunakan lebih banyak fosfat yg ada dalam tanah 3. Kombinasi keduanya …………………..

34 Fiksasi P-pupuk, % Pasio R2O3 : P2O5

35 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 insoluble 4. Pd tnh masam: Fe-P dan Al-P yg insoluble 5. Al mono-kalsium fosfat Al(OH) 2 H 2 PO 4 (liming with phosphorus) 6. Kapasitas fiksasi P = F(oksida Fe dan Al; Al dd ) 7. Intensitas Fiksasi P: Oksida > Oksida > Liat 1:1 > Liat 2:1 amorf kristalin

36 Tanah Liat dominan % Liat Fixed P (ppm) Adsorpsi Max. Pd 0.2 ppm P lrt tnh Inceptisol Montmorilonit Ultisol Kaolinit Oxisol Kaolinit Andept Alofan Sumber: NCSU, 1973

37 1. H 2 PO 4 - dlm larutan tanah < 10 ppm, dlm tanaman 2000 ppm 2. Konsentrasi optimum unt jagung dan buncis: 0.07 ppm pd tnh berliat Ultisol, Oxisol 0.2 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 P 5. Liat oksida & Alofan > Kaolinit > Montmorilonit 6. Uji tanah untuk P : mengekstraks sejumlah P-tersedia dlm tanah yg berkorelasi dg respon tanmn thd pemupukan P 7. Tingkat kritis hasil uji tanah sekitar ppm P dlm larutan tanah

38 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; CaHPO4 2. Hidroksi-apatit 3. 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 CO 3 = atau OH- Reaksi retensi fosfat oleh liat-liat yang jenuh kalsium: Liat-Ca-H 2 PO 4 Tiga faktor penting: 1. Aktivitas Ca++ 2. Jumlah dan ukuran partikel CaCO 3 bebas 3. Jumlah liat yang ada dlm tanah …………………..

39 P-aded (ppm) P dlm larutan tanah, ppm Oxisol, 45% liat Andept Ultisol, 38% liat Tnh Montmorilonit, 40% liat Sumber: Fox, 1974

40 Tanaman Hasil, t/haP-removal, kg/ha 1. JagungBiji: Jerami: Biji: Jerami: PadiBiji: Jerami: Biji: Jerami: NanasBuah: Tebu2 thAbove ground: Sumber: Sanchez, 1976.

41 Hasil relatif (%) P- larutan tanah, ppm Ubijalar: toleran tanah miskin P Jagung: intermediate Lettuce: In-tolerant

42 TanamanP-larutan tnh yg menghasilkan 95% hasil maks., ppm 1. Lettuce Tomat Cucumber Kedelai (vegetable) Ubijalar Jagung Sorghum Kubis0.04 Sumber: Fox et al. (1974)

43 TanamanInternal P Requirement, %P 1. Stylosanthes humilis Centrosema pubescens Desmodium intortum Digitaria decumbens Panicum maximum Pennisetum clandestinum Paspalum dilatatum Sumber: Andrew & Robins (1969, 1971)

44 TEKNOLOGI PEMUPUKAN FOSFAT : 1. Respon pupuk P sgt tinggi pada Oxisol, Ultisol, andepts, Vertisols 2. Dosis pupuk P = F (jenis tanaman, tanah, cara aplikasi, musim) 3. Dosis Rekomendasi Jagung, kedelai, Tebu: kg P 2 O 5 /ha 4. Kapasistas fiksasi P tanah menentukan cara aplikasi pupuk P: Disebar, ditugal, digarit, pd lubang tanam, dll 5. Pada tanah yg memfiksasi P ada dua strategi: 1. Dosis medium, digarit, setiap musim tanam 2. Dosis tinggi unt menjenuhi kapasitas fiksasi P-tanah, dan efek residunya berlangsung beberapa tahun 6. Pupuk P yg baik harus mengandung % P dlm bentuk larut air, untuk memenuhi kenbutuhan awal pertumbuhan tanaman 7. Aplikasi kapur & silikat mampu menurunkan fiksasi P dlm tanah 8. Pengapuran hingga pH umumnya meningkatkan ketersediaan P dalam tanah, mengurangi fiksasi P

45 Hasil biomasa, % Pemupukan P (ppm P) Sumber: Mendez-Lay (1974), Tnh Oxisol. Tingkat kritis Tdk dipakur pH= 4.8 Dikapur hingga pH = 5.5

46 Kapasitas fiksasi P tanah sngt tinggi, alternatif pengelolaan: 1. Kombinasi cara aplikasi pupuk P: ditugal/digarit dg sebar 2. Batuan-fosfat larut sitrat 3. Aplikasi kapur atau Ca-silikat unt ngurangi fiksasi P 4. Kultivar tanaman yg toleran thd larutan tanah yg miskin fosfat 5. Pertimbangan biaya pupuk & pemupukan.

47 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 CO 3 = atau OH- Reaksi retensi fosfat oleh liat-liat yang jenuh kalsium: Liat-Ca-H 2 PO 4 Tiga faktor penting: 1. Aktivitas Ca++ 2. Jumlah dan ukuran partikel CaCO 3 bebas 3. Jumlah liat yang ada dlm tanah …………………..

48 MONO KALSIUM FOSFAT Granula Monokalsium fosfat: H 2 O H 2 O H 2 O 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

49 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.

50 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.

51 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

52 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 larutan tanah P terjebak oleh selimut Selimut oksida Fe atau Al

53 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: ……… 27/3/2013 PO4 terlarut Larutan Tanah BO hidup BO mati Erosi tanah BinatangTanaman Pupuk kimia PO4 terjerap PO4 mengendap Fe, Al, Ca Mineral tanah Rabuk Kompos Humus Sistem Tanah

54 Diunduh dari: ……… 27/3/2013 SIKLUS P DALAM TANAH (Dean Hesterberg, 2010) P-mineral Ca-fosfat Fe-fosfat Al-fosfat P-terjerap P-teroklusi PO4-Fe-oksida PO4-Al-oksida PO4-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 ( % Pt bagian di atas tanah) P-panen tanaman Bahan pembenah ( % Pt (pupuk, rabuk, biosolid) P-runoff (<0.15% Pt) Terlarut dan partikulat

55 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: NUTRITION-FORMS-IN-THE-SOIL-PLANT-UPTAKE-AND-PLANT-RESPONSE ……… 27/3/2013 P-larutan P-labil P Tidak labil

56 (Sumber: Sharpley and Sheffield, Livestock and Poultry Environmental Stewardship Curriculum) Diunduh dari: ……… 27/3/2013 SIKLUS P-TANAH Panen Tanaman Sisa panen Aplikasi Pupuk P Aplikasi P Rabuk P-AnorganikP-Organik P- Uji Tanah P-larutan Labil Stabil LabilStabil Tanaman

57 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: ……… 27/3/2013 P - larutan 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

58 SIKLUS P DALAM TANAH Diunduh dari: ……… 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"

59 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: ……… 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:

60 Options for managing soil phosphorus supply Dr. 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 tanaman 3.Memaksimumkan efisiensi pemanfaatan P oleh tanaman. Diunduh dari: ……… 27/3/2013

61 Options for managing soil phosphorus supply Dr. Ann McNeill School of Earth & Environmental Sciences, University of Adelaide, South Australia. 21st July 2008 Diunduh dari: ……… 27/3/2013 Soil P cycle - pools and pathways. Modified from [McLaughlin et al. 1999, 1] Cadangan biomasa mikroba Po Labil Po tidak-Labil FASE ORGANIK Pi dapat ditukar Pi tidak-dapat ditukar MINERAL CADANGAN LARUTAN TANAH P -Organik + anorganik Pertukaran kontak Adsorpsi Desorpsi Pengendapan Asimilasi Dekomposisi BO Mineralisasi Non- asimilatory Mineralisasi Imobilisasi Penyerapan akar ekskresi akar

62 The value of phosphorus in crop stubble Sarah 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: ……… 27/3/2013 P mikroba P labil P larutan P tdk tersedia P dalam Tanaman P dalam Seresah sisa panen

63 KETERSEDIAAN P DALAM TANAH Fosfat mudah diikat dna menjadi bagian dari senyawa kalsium, besi dan aluminum dalam tanah: 1.Only % 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 P 5.Semakin rendah lengas tanah = semakin rendah ketersediaan P 6.Semakin rendah suhu tanah = semakin rendah ketersediaan P Diunduh dari: soils/Pages/default.aspx ……… 27/3/2013

64 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: 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

65 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 (k 1 ’) seimbang (korelasinya kuat) dengan jumlah P yg diserap oleh tanaman (k 1 ) atau hasil tanaman, maka uji tanah ini cocok untuk kalibrasi rekomendasi dosis pupuk berdasar P-larut air. Diunduh dari: ……… 27/3/2013

66 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.

67 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 % fosfat larut air dapat bergerak ke luar dari granula pupuk dalam periode 24 jam.

68 UJI P-TANAH: PRINSIP DAN ANALISISNYA

69 Soil Test Phosphorus: Principles and Overview J. 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

70 Soil Test Phosphorus: Principles and Overview J. Thomas Sims, University of Delaware 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. Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

71 Soil Test Phosphorus: Principles and Overview J. Thomas Sims, University of Delaware Komponen mendasar dalam program uji P-tanah. Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013 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 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.

72 Soil Test Phosphorus: Principles and Overview J. Thomas Sims, University of Delaware Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013 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.

73 Soil Test Phosphorus: Bray and Kurtz P-1 J. 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). Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

74 Soil Test Phosphorus: Bray and Kurtz P-1 J. Thomas Sims, University of Delaware In soils such as these, the acidity of the extracting solution can be neutralized unless the 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 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. Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

75 Soil Test Phosphorus: Bray and Kurtz P-1 J. Thomas Sims, University of Delaware Peralatan lab: 1.Ayakan No. 10 (diameter lubang 2 mm) 2.Standard 1 g and 2 g stainless steel soil scoops 3.Automatic extractant dispenser, 25 mL capacity 4.Extraction vessels, such as 50 mL Erlenmeyer flasks, and filter funnels (9 and 11 cm) and racks 5.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.) Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

76 Soil Test Phosphorus: Bray and Kurtz P-1 J. Thomas Sims, University of Delaware Reagen = Pereaksi: Bray and Kurtz P-1 Extracting Solution (0.025 M HCl in 0.03 M NH4F): Dissolve 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 ± Penyesuaian pH dilakukan dnegan menggunakan HCl atau NH 4 OH. Simpan dalam polyethylene-carboys hingga saatnya digunakan. Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

77 Soil Test Phosphorus: Bray and Kurtz P-1 J. Thomas Sims, University of Delaware 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. Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

78 Soil Test Phosphorus: Bray and Kurtz P-1 J. Thomas Sims, University of Delaware Perhitungan: P yg terekstraks dnegan metode Bray & Kurtz P-1 dihitung : P-terekstraks Bray & Kurtz P – 1 (mg P/kg tanah ) = (C P x [0.020 L ekstraks] ) / kg tanah dimana: C P = Konsentrasi P dalam ekstraks Bray & Kurtz P-1, mg/L. Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013 References: 1.Bray R.H., and L.T. Kurtz Determination of total, organic and available forms of phosphorus in soils. Soil Sci. 59: Frank, K.D. Beegle, and J. Denning Phosphorus. p 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 Greenhouse evaluation of four phosphorus soil tests in relation to phosphate buffering and labile phosphate in soils. Soil Sci. Soc. Am. J. 44:

79 Soil Test Phosphorus: Olsen P J. Thomas Sims, University of Delaware The “Olsen P” or sodium bicarbonate soil test phosphorus (P) method was developed by 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. Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

80 Soil Test Phosphorus: Olsen P J. Thomas Sims, University of Delaware 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. Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

81 Soil Test Phosphorus: Olsen P J. Thomas Sims, University of Delaware Peralatan Lab: 1.Ayakan No. 10 (diameter lubang 2 mm) 2.Standard 1 g and 2 g stainless steel soil scoops 3.Automatic extractant dispenser, 25 mL capacity 4.Extraction vessels, such as 50 mL Erlenmeyer flasks, and filter funnels (9 and 11 cm) and racks 5.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.) Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

82 Soil Test Phosphorus: Olsen P J. Thomas Sims, University of Delaware 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. Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

83 Soil Test Phosphorus: Olsen P J. Thomas Sims, University of Delaware 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 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.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. Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

84 Soil Test Phosphorus: Olsen P J. Thomas Sims, University of Delaware Perhitungan: P terekstraks Olsen (mg P/kg tanah) = [Konsentrasi P dalam ekstraks Olsen, mg/L ] x [ L ekstrak ÷ kg tanah] Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013 References: 1.Fixen, P.E. and J.H. Grove Testing soils for phosphorus. p In R.L. Westerman (ed.) Soil Testing and Plant Analysis. SSSA, Madison, WI. 2.Kuo, S Phosphorus. p 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 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 Sodium bicarbonate extractable P, K, and N. p In M. R. Carter (ed.) Soil Sampling and Methods of Analysis. Can. Soc. Soil Sci., Ottawa, Ontario.

85 Soil Test Phosphorus: Mehlich 1 J. 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). Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

86 Soil Test Phosphorus: Mehlich 1 J. Thomas Sims, University of Delaware Nilai P Mehlich-1 sebesar 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). Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

87 Soil Test Phosphorus: Mehlich 1 J. Thomas Sims, University of Delaware Peralatan Lab: 1.No. 10 (2 mm opening) sieve 2.Automatic extractant dispenser, 25 mL capacity (If preferred, pipettes are acceptable.) 3.Standard 5 cm3 and 1 cm3 stainless steel soil scoops 4.Extraction vessels, such as 50 mL Erlenmeyer flasks, and filter funnels (9 and 11 cm) and racks 5.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.) Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

88 Soil Test Phosphorus: Mehlich 1 J. Thomas Sims, University of Delaware Pereaksi - Reagents: Mehlich 1 Extracting Solution ( M H2SO 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. Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

89 Soil Test Phosphorus: Mehlich 1 J. Thomas Sims, University of Delaware 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. 2.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. 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 [ L ekstrak ÷ kg tanah] Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

90 Soil Test Phosphorus: Mehlich 1 J. Thomas Sims, University of Delaware References: 1.Kamprath, E.J. and M.E. Watson Conventional soil and tissue tests for assessing the phosphorus status of soils. p In F. E. Khasawneh et al. (ed.) The role of phosphorus in agriculture. ASA, CSSA, and SSSA, Madison, WI. 2.Kuo, S Phosphorus. p 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 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: Mehlich, A 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 The development, evaluation, and use of soil tests for phosphorus availability. Agronomy 4: Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

91 Soil Test Phosphorus: A Phosphorus Sorption Index J. 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. Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

92 Soil Test Phosphorus: A Phosphorus Sorption Index J. Thomas Sims, University of Delaware 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. Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

93 Soil Test Phosphorus: A Phosphorus Sorption Index J. Thomas Sims, University of Delaware 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 mL screw-top test tubes. Reagen: Phosphorus Sorption Solution (75 mg P/L): Dissolve g of monobasic potassium phosphate (KH2PO4) in 1 L of deionized H2O. Store in refrigerator until use. Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

94 Soil Test Phosphorus: A Phosphorus Sorption Index J. Thomas Sims, University of Delaware 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). Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

95 Soil Test Phosphorus: A Phosphorus Sorption Index J. Thomas Sims, University of Delaware 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). Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

96 Soil Test Phosphorus: A Phosphorus Sorption Index J. Thomas Sims, University of Delaware References: 1.Bache, B.W., and E.G. Williams A phosphate sorption index for soils. J. Soil Sci. 22: Mozaffari, P.M., and J.T. Sims Phosphorus availability and sorption in an Atlantic Coastal Plain watershed dominated by intensive, animal-based agriculture. Soil Sci. 157: Nair, P.S., T.J. Logan, A.N. Sharpley, L.E. Sommers, M.A. Tabatabai, and T.L. Yuan Interlaboratory comparison of a standardized phosphorus adsorption procedure. J. Environ. Qual. 13: Sharpley, A.N., S.J. Smith, B.A. Stewart, and A.C. Mathers Forms of phosphorus in soils receiving cattle feedlot waste. J. Environ. Qual. 13: Simard, R.R., D. Cluis, G. Gangbazo, and A. Pesant Phosphorus sorption and desorption indices for soils. Commun. Soil Sci. Plant Anal. 25: Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

97 Determination of Water- and/or Dilute Salt-Extractable Phosphorus M.L. Self-Davis, University of Arkansas P.A. Moore, Jr., USDA-ARS, Fayetteville, AR B.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). Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

98 Determination of Water- and/or Dilute Salt-Extractable Phosphorus M.L. Self-Davis, University of Arkansas P.A. Moore, Jr., USDA-ARS, Fayetteville, AR B.C. Joern, Purdue University 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: 1.Asam pekat hydrochloric acid (HCl). 2.Reagents used for ascorbic acid technique for P determination, Murphy and Riley (1962). 3.Larutan M calcium chloride (CaCl2). 4.Chloroform. Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

99 Determination of Water- and/or Dilute Salt-Extractable Phosphorus M.L. Self-Davis, University of Arkansas P.A. Moore, Jr., USDA-ARS, Fayetteville, AR B.C. Joern, Purdue University 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. Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

100 Determination of Water- and/or Dilute Salt-Extractable Phosphorus M.L. Self-Davis, University of Arkansas P.A. Moore, Jr., USDA-ARS, Fayetteville, AR B.C. Joern, Purdue University Prosedur Ekstraksi M 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. Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

101 Determination of Water- and/or Dilute Salt-Extractable Phosphorus M.L. Self-Davis, University of Arkansas P.A. Moore, Jr., USDA-ARS, Fayetteville, AR B.C. Joern, Purdue University 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] Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

102 Determination of Water- and/or Dilute Salt-Extractable Phosphorus M.L. Self-Davis, University of Arkansas P.A. Moore, Jr., USDA-ARS, Fayetteville, AR B.C. Joern, Purdue University References: 1.Lee, G.R., N.L. Clesceri, and G.P. Fitzgerald Studies on the analysis of phosphates in algal cultures. Internat. J. Air Water Poll. 9: Luscombe, P.C., J.K. Syers, and P.E.H. Gregg Water extraction as a soil testing procedure for phosphate. Commun. Soil Sci. Plant Anal. 10: Murphy, J., and J.P. Riley A modified single solution method for the determination of phosphate in natural waters. Anal. Chem. Acta 27: Olsen, S.R., and L.E. Sommers Phosphorus. P 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 Diffusive supply of phosphorus in relation to soil textural variations. Soil Sci. 110: Pote, D.H., T.C. Daniel, P.A. Moore, Jr., A.N. Sharpley, D.R. Edwards, and D.J. Nichols 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 Relating extractable soil phosphorus to phosphorus losses in runoff. Soil Sci. Soc. Am J. 60: Sharpley, A.N Dependence of runoff phosphorus on extractable soil phosphorus. J. Environ. Qual. 24: Soltanpour, P.N., F. Adams, and A.C. Bennett Soil phosphorus availability as measured by displaced soil solutions, calcium chloride extracts, dilute-acid extracts, and labile phosphorus. Soil Sci. Soc. Am. Proc. 38: Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

103 Bioavailable Phosphorus in Soil Andrew 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. Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

104 Bioavailable Phosphorus in Soil Andrew Sharpley, USDA-ARS, University Park, PA 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. Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

105 Bioavailable Phosphorus in Soil Andrew Sharpley, USDA-ARS, University Park, PA 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. Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

106 Bioavailable Phosphorus in Soil Andrew Sharpley, USDA-ARS, University Park, PA Iron-oxide-Impregnated Paper Another P sink that has received attention is Fe-oxide impregnated filter paper, which has 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. Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

107 Bioavailable Phosphorus in Soil Andrew Sharpley, USDA-ARS, University Park, PA 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). Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

108 Bioavailable Phosphorus in Soil Andrew Sharpley, USDA-ARS, University Park, PA 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). Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

109 Bioavailable Phosphorus in Soil Andrew Sharpley, USDA-ARS, University Park, PA 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. Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

110 Bioavailable Phosphorus in Soil Andrew Sharpley, USDA-ARS, University Park, PA 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 sink 3.Labu Volumetrik – biasanya volume 25 atau 50 mL 4.Pipets untuk sampel aliquot dan reagen warna 5.Spectrophotometer untuk menentukan konsentrasi P dalam reagen yg menjadi berwarna kalau ketemu sampel. Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

111 Bioavailable Phosphorus in Soil Andrew Sharpley, USDA-ARS, University Park, PA Reagents: Membran Resin Hydrochloric acid to extract P from the membranes M HCl (166 mL concentrated HCl in 2 L) Murphy and Riley Molybdenum Blue Color Reagent Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

112 Bioavailable Phosphorus in Soil Andrew Sharpley, USDA-ARS, University Park, PA 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. Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

113 Bioavailable Phosphorus in Soil Andrew Sharpley, USDA-ARS, University Park, PA Perhitungan: P-terekstraks Resin (mg P/kg) = [Konsentrasi P dalam 1 MHCl, mg/L] x [0.04 L ÷ 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 Bioavailability index for phosphorus using nonexchange resin impregnated membranes. Soil Sci. Soc. Am. J. 56: Amer, F., D.R. Bouldin, C.A. Black, and F.R. Duke Characterization of soil phosphorus by anion exchange resin and adsorption by P-32 equilibration. Plant Soil 6: Barrow, N.J., and T.C. Shaw Factors affecting the amount of phosphate extracted from soil by anion exchange resin. Geoderma 18: Butkus, S.R., E.B. Welch, R.R. Horner, and D.E. Spyridakis Lake response modeling using biologically available phosphorus. J. Water Pollut. Cont. Fed. 60: Chardon, W.J 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 Dorich, R.A., D.W. Nelson, and L.E. Sommers Algal availability of sediment phosphorus in drainage water of the Black Creek watershed. J. Environ. Qual. 9: Edwards, T., B. Ferrier, and R. Harriman Preliminary investigation on the use of ion-exchange resins for monitoring river water composition. Sci. of Total Environ. 135: Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

114 Total Phosphorous in Soil M.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 extraction are 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. Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

115 Total Phosphorous in Soil M.R. Bender and C.W. Wood, Auburn University In recent years, more rapid methods for determining total P in soils have been developed (Sommers and Nelson, 1972; Dick and Tabatabai, 1977; Bowman, 1988). Methods developed by Sommers and Nelson (1972) and Bowman (1988) are variations of 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. Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

116 Total Phosphorous in Soil M.R. Bender and C.W. Wood, Auburn University Fusion Method (Olsen and Sommers (1982)): Reagents 1.Anhydrous sodium carbonate (Na2CO3) 2.Larutan 4.5 M H2SO4 3.Larutan 1 M H2SO4 4.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 H2SO4 6.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 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. Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

117 Total Phosphorous in Soil M.R. Bender and C.W. Wood, Auburn University 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) Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

118 Total Phosphorous in Soil M.R. Bender and C.W. Wood, Auburn University KOMENTAR The method for color development was described by Harwood et al. (1969) and is a variation 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] Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

119 Total Phosphorous in Soil M.R. Bender and C.W. Wood, Auburn University 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 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 H 2 SO 4. 5.Persiapkan reagen setiap mingguan. Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

120 Total Phosphorous in Soil M.R. Bender and C.W. Wood, Auburn University 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] Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

121 Total Phosphorous in Soil M.R. Bender and C.W. Wood, Auburn University Metode Oksidasi Alkaline (Dick and Tabatabai (1977)): Pereaksi - Reagents 1.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 acid 3.Larutan 2.5 M H2SO4 4.Ammonium molybdate -Antimony potassium tartrate solution. Prepare by dissolving 12 g of ammonium molybdate in 250 mL of distilled water, and dissolving 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 g of ascorbic acid in 200 mL of ammonium molybdate - antimony reagent. Prepare reagent daily. 6.Standard phosphate solution. Prepare by dissolving g of potassium dihydrogen phosphate (KH2PO4) in distilled water. Dilute solution to 1L with distilled water. Standard solution contains 50 mg P/L. Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

122 Total Phosphorous in Soil M.R. Bender and C.W. Wood, Auburn University Prosedur kerja 1.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. Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

123 Total Phosphorous in Soil M.R. Bender and C.W. Wood, Auburn University 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] Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

124 Total Phosphorous in Soil M.R. Bender and C.W. Wood, Auburn University References: 1.Bowman, R.A A rapid method to determine total phosphorus in soils. Soil Sci. Soc. Am. J. 52: Bray, R.H., and L.T. Kurtz Determination of total, organic, and available forms of phosphorus is soils. Soil Sci. 59: Dick, W.A., and M.A. Tabatabai An alkaline oxidation method for determination of total phosphorus in soils. Soil Sci. Soc. Am. J. 41: Harwood, J.E., R.A. van Steenderen, and A.L. Kuhn A rapid method for orthophosphate analysis at high concentrations in water. Water Res. 3: Jackson, M.L Soil chemical analysis. Prentice-Hall, Inc., Englewood Cliffs, N.J. Muir, J.W The determination of total phosphorus in soil. Analyst 77: Murphy, J., and J.P. Riley A modified single solution method for determination of phosphate in natural waters. Anal. Chim. Acta 27: Olsen, S.R., and L.E. Sommers Phosphorus. pp 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 An evaluation of methods for the determination of total phosphorus in soils. N.Z.J. Agric. Res. 9: Sommers, L.E., and D.W. Nelson Determination of total phosphorus in soils: a rapid perchloric acid digestion procedure. Soil Sci. Soc. Amer. Proc. 36: Syers, J.K., J.D.H. Williams, A.S. Campbel, and T.W. Walker The significance of apatite inclusions in soil phosphorous studies. Soil Sci. Soc. Amer. Proc. 31: Syers, J.K., J.D.H. Williams, and T.W. Walker The determination of total phosphorus in soils and parent materials. N.Z.J. Agric. Res. 11: Diunduh dari: https://secure.hosting.vt.edu/...vt.../Methods_of_P_Analysis_2000.pd... ……… 27/3/2013

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