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MK. Dasar Ilmu Tanah bahan kajian: FOSFAT DALAM TANAH diabstraksikan Oleh soemarno.jursntnhfpub. Okt 2012.

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2 MK. Dasar Ilmu Tanah bahan kajian: FOSFAT DALAM TANAH diabstraksikan Oleh soemarno.jursntnhfpub. Okt 2012

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

4 FOSFAT - TANAH The Soil P Cycle In the soil, not all phosphorus is the same. It can be a part of organic molecules or part of inorganic molecules. In addition, the chemicals that contain P will change in the soils. Therefore, it is important to think about the P cycle in the soil. The availablity of soil P to plants is dependent on the reactions of different chemical forms of soil P. Phosphorus inputs to the soil are primarily from the application of fertilizer P and organic resources which contain P, such as manure. Lesser amounts may be added due to deposition from the atmosphere and sedimentation. Soil P is generally categorized into three types: solution P, labile P, and non-labile P. diunduh dari: ….. The soil P cycle. (Image from Sharpley and Sheffield, Livestock and Poultry Environmental Stewardship Curriculum)Livestock and Poultry Environmental Stewardship Curriculum

5 FOSFAT - TANAH Phosphorus (P) Phosphorus, another of the macro- nutrients is required in significant quantities by a cotton crop. It is taken up by the plant primarily as orthophosphate with the predominate form being highly dependent upon soil pH (PO43- at high pH; HPO42- at moderate pH; and H2PO4- at low pH). Utilization of the P nutrient in the plant is primarily associated with energy transfer with the molecules ATP and ADP. Phosphorus nutrition has also been shown to play an important role in the synthesis of cellular membranes (phospholipids) which help maintain cellular integrity. The amount that needs to be supplied through supplemental fertilization varies across the belt. However soil testing has proven to be an effective method of determining the need for supplemental P fertilization. diunduh dari: ….. Soil phosphorus dynamics including potential tranformations and fates of applied fertilizer P.

6 FOSFAT - TANAH Process-based assessment of plant-available soil P 1.Achat David L, Bakker Mark R, Morel Christian, Process-based assessment of P availability in a low P- sorbing forest soil using isotopic dilution methods. Soil Sci Soc Am J 73: ; Achat David L, Bakker Mark R, Augusto Laurent, Saur Etienne, Dousseron Lysiane, Morel Christian Evaluation of the phosphorus status of P-deficient podzols in temperate pine stands combining isotopic dilution and extraction methods. Biogeochemistry, 92, 183: Morel C., H. Tiessen, J.O. Moir and J.W.B. Stewart, Phosphorus transformations and availability under cropping and fertilization assessed by isotopic exchange. Soil Science Society of American Journal, 58 : diunduh dari: ….. aquitaine.inra.fr/tcem_eng/recherche/nutrition_minerale_et_gestion_de_la_fertilite

7 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

8 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

9 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

10 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)

11 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

12 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)

13 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

14 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)

15 FOSFAT - TANAH Adequate P supply is important at early stages of the plant growth and at the development of reproductive plant organs. Phosphorus is also needed for adequate root development and crop maturity. Large amounts of phosphorus are found in seeds and fruits. Adequate P supply improves the quality of certain fruits, forage and vegetables. It also increases plant resistance to diseases, winter damage, and unfavourable growing conditions. Phosphorus is mobile in plants. When P deficiencies occur, P moves from old to young, more active tissues. A purple discoloration of leaves or leaf edges is a common symptom of P deficiencies. diunduh dari: ….. Schematic representation of P cycle in soil

16 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.

17 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. ….. 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. …..

18 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.

19 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

20 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

21 FOSFAT - TANAH Crop P demand and soil P tests Grain yield potential is set by water (and nutrient) availability in the pre-anthesis period while actual yield is determined by post-anthesis water (and nutrient) availability. Under conditions where the crop is reliant on stored subsoil water for growth, P is acquired from sub-surface layers (10-30 cm) for much of the growing season. Because the root surface area for P absorption increases as the crop grows, slowly available P sourced from the dissolution of sparingly soluble soil minerals and fertiliser reaction products (‘reserve P’) becomes increasingly important as the crop matures (Wang et al. 2007). While these reserve P sources can be quantified using an acid soil P test such as the BSES-P test (0.005 M sulphuric acid extractant), the actual quantity of this P that is available is dependent on the ability of the root system (which may be mycorrhizal) to lower the soil solution P concentration below the threshold value where these reserve P sources start to dissolve. This threshold value will vary depending on the chemical composition of the P source and its degree of crystallinity. Therefore it is a major challenge to develop soil P tests capable of determining how much ‘reserve’ P is available. diunduh dari: available-for-plant-uptake ….. How much of the soil P is available for plant uptake? Phil Moody 1, Grant Pu 1 and Mike Bell 2 1 DERM, Dutton Park, 4102 Qld 2 QAAFI, Kingaroy, 4610 Qld Conceptual diagram of P pools extracted by the Colwell-P method.

22 FOSFAT - TANAH The soil P pools and the relative efficiency of Colwell-P (0.5 M sodium bicarbonate) and BSES-P (0.005 M sulphuric acid) for extracting P from these pools. Reserve P comprises the calcium phosphate minerals and fertiliser reaction products. Conceptually, this reserve P supply can be likened to a trickle supply, and the question of whether this trickle supply is sufficient for the crop to achieve maximum growth was addressed by undertaking a soil P depletion experiment with forage sorghum in glasshouse trials. The fate of P applied to P- depleted soils was then determined in a P addition experiment using the soils from the P depletion trial. diunduh dari: available-for-plant-uptake ….. Conceptual diagram of P pools extracted by the BSES-P method

23 FOSFAT - TANAH. Soil tests for assessment of available P Crop P uptake A plot of cumulative crop P uptake against initial Colwell-P indicates a close linear relationship (Fig.2). The BSES-P values of soils with less than 15 mg/kg Colwell-P (i.e. expected to be P deficient) but more than 45 mg/kg BSES-P are identified in Figure. Three of the soils with BSES-P ranging from mg/kg lie above the regression line, indicating that some of the BSES-P is available, but there is no consistent trend for available P to increase with higher BSES-P. Soil 12 with 794 mg/kg BSES-P lies below the regression line, but the dry matter yield and p uptake of this soil was compromised by salinity and sodicity. These results show that it is not possible to use BSES-P as a quantitative measure of the available reserve P. BSES-P levels relative to Colwell-P should rather be used to indicate whether there is a lot, or a little, of reserve P. diunduh dari: available-for-plant-uptake ….. Plot of cumulative crop P uptake against Colwell- P for 15 soils used in the glasshouse depletion experiment.

24 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? …………

25 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 …………………………..

26 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 …………………..

27 Fiksasi P-pupuk, % Pasio R2O3 : P2O5

28 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

29 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

30 Path and Multiple Regression Analyses of Phosphorus Sorption Capacity H. Zhang, J. L. Schroder, J. K. Fuhrman, N. T. Basta, D. E. Storm and M. E. Payton Sssaj 2005 Vol. 69 No. 1, p diunduh dari: https://www.soils.org/publications/sssaj/abstracts/69/1/0096?access=0&view=article ….. Soil P saturation indices and P Langmuir adsorption maximum (S max ) are two environmental soil tests that provide valuable information for the proper management P in soils to avoid the overapplication of P. The objectives of this study were to determine S max and develop P saturation indices for 28 Oklahoma benchmark soils and to use path analysis and multiple regression to examine the relationships between S max and soil properties. Soil samples were analyzed for pH, clay content, oxalate extractable P (P ox ), Al (Al ox ), Fe (Fe ox ), and Mehlich-3 (M3) extractable P (P M3 ), Al (Al M3 ), Fe (Fe M3 ), Ca (Ca M3 ), and Mg (Mg M3 ). The S max value and saturation indices based on oxalate and M3 extractions were determined. The S max value ranged from 34 to 500 mg kg −1 and was highly correlated with clay content (r = 0.79), organic C (r = 0.80), Al ox (r = 0.88), and Fe ox (r = 0.83). Soil pH was not correlated (p > 0.05) with S max Path analysis showed significant direct effects (p < 0.01) between Al ox and S max and between Fe ox and S max but these relationships were highly influenced by indirect effects of Al ox and Fe ox Multiple regression agreed well with path analysis and found that the combination of Al ox and Fe ox were the two most important soil properties related to S max of the soils studied. Significant relationships existed between Al M3 (r = 0.54) and S max and between Fe M3 (r = 0.54) and S max Three P saturation indices studied were highly correlated (p < 0.05) with each other. Our results show that S max of Oklahoma soils may be predicted with oxalate extractable Al and Fe or M3 extractable Al, Fe, and Ca.

31 Path and Multiple Regression Analyses of Phosphorus Sorption Capacity H. Zhang, J. L. Schroder, J. K. Fuhrman, N. T. Basta, D. E. Storm and M. E. Payton Sssaj 2005 Vol. 69 No. 1, p diunduh dari: https://www.soils.org/publications/sssaj/abstracts/69/1/0096?access=0&view=article …..

32 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

33 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 …………………..

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

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

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

37 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)

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

39 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

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

41 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.

42 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 …………………..

43 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

44 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.

45 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.

46 HASIL-HASIL PENELITIAN FOSFAT-TANAH

47 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. This paper discusses potential agronomic strategies to assist in sustainable management of the soil P resource in Australian 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. Three broad options for P management are considered: 1.Importing P as fertilisers, either mineral or organic, 2.Practices for increasing soil P cycling to facilitate release and synchronous uptake of plant-available P, and 3.Approaches for maximising the P use-efficiency of crops and pasture species in the system. diunduh dari: ….

48 Options for managing soil phosphorus supply Dr. Ann McNeill School of Earth & Environmental Sciences, University of Adelaide, South Australia. 21st July 2008 P cycle, soil organic matter, microbes and mycorrhizae Phosphorus can exist in many different forms in soil, from readily plant-available sources such as mineral phosphate and easily-converted labile organic P compounds, to highly insoluble forms including P in some complex organic matter compounds and P ‘fixed’ by soil minerals. The soil type (texture and pH in particular) and the organic matter content influence how P behaves in the soil, the pathways it follows and where it ends up. Ultimately the goal of the producer is to maximise P uptake into the plant. Soil organic matter (SOM) is important for a number of physical, chemical and biological functions. It changes relatively slowly over time but can be increased as long as inputs are greater than outputs; i.e. more carbon goes in as roots and residues than comes out via respiration. Soil microbes are part of the SOM. diunduh dari: …. Soil P cycle - pools and pathways. Modified from [McLaughlin et al. 1999] McLaughlin MJ, Reuter DJ, Rayment GE (1999) Soil testing - principles and concepts. In ‘Soil analysis - an interpretation manual’. (Eds KI Peverill, LA Sparrow and DJ Reuter) pp. 1–21. (CSIRO publishing: Collingwood, VIC).

49 Options for managing soil phosphorus supply Dr. Ann McNeill School of Earth & Environmental Sciences, University of Adelaide, South Australia. 21st July 2008 Another soil microorganism, beneficial soil fungi called mycorrhizae, can contribute to the uptake of P by plants, although the process is very complex and the details of the processes involved are still the subject of much research. These fungi colonise plant roots and also explore large volumes of soil with their extensive networks of fungal hyphae. A range of direct and less direct mechanisms has been suggested including: 1.Increased physical exploration of the soil; 2.Increased P movement into mycorrhizal hyphae; 3.Modification of the root environment; 4.Efficient transfer of P to plant roots; 5.Increased storage of absorbed P; and 6.Efficient utilisation of P within the plant. diunduh dari: ….

50 Options for managing soil phosphorus supply Dr. Ann McNeill School of Earth & Environmental Sciences, University of Adelaide, South Australia. 21st July 2008 Fertilisers, manures, composts and biosolids as sources of P When soluble granular P fertilisers are applied to soil, a large proportion of the P quickly dissolves (within 24 hrs) but there are many fates for that dissolved P once it gets into the soil solution pool. The concentration of P around the fertiliser granule is high, and P may be lost from the soil solution pool by precipitation reactions, where soluble P combines with other elements in the soil (calcium, aluminium, iron) to produce new solid compounds. Some of these new compounds can eventually dissolve over time, or when a plant root reaches them, to release P into a soluble form again. However, some P compounds can remain very insoluble and are therefore ‘locked up’ in the non-exchangeable pool and effectively unavailable for plant uptake. As P moves away from the granule through soil pores it binds to soil surfaces by a process called adsorption. This is where P is attracted to the clay mineral surfaces of soils; some of the P on the surface remains in a plant-available form (i.e. it can move back into the soil solution pool) but some may be very strongly bound and permanently removed from the plant-available pool into the non-exchangeable pool diunduh dari: ….

51 Options for managing soil phosphorus supply Dr. Ann McNeill School of Earth & Environmental Sciences, University of Adelaide, South Australia. 21st July 2008 Increasing P cycling - residues and rotations Practices that increase organic matter in soil should, generally, increase the capacity to cycle P. Thus, at the Wagga Wagga long term trial site in south-eastern Australia, organic P increased over 24 years in the rotations with a mulched subterranean clover pasture component, especially with direct-drill. Losses of organic P were largest (–42 kg P/ha) under continuous wheat with stubble burning and cultivation ([Bunemann et al. 2006, 13]).[Bunemann et al. 2006, 13] The pattern of changes in organic P in the Wagga Wagga trial caused by agricultural management was closely correlated to changes in organic matter carbon (C). This link between organic C and organic P was also evident in a survey of 10 sites across southern Australia with different land use, including three sites from NSW. The data showed that organic P was highest where organic C input was high, such as under trees or in grassland and pastures, and lowest in wheat-fallow situations particularly with stubble-burning and cultivation. 1.Bunemann EK, Heenan D, Marschner P, McNeill A (2006) Long term effects of crop rotation, stubble management and tillage on soil phosphorus dynamics. Australian Journal of Soil Research 44, 611–618. diunduh dari: ….

52 Formation of Apatite from Superphosphate in the Soil G. NAGELSCHMIDT & H. L. NIXON Nature 154, (30 September 1944) | doi: /154428b0 THE bulk of the phosphate added to soils as fertilizer remains in forms unavailable to plants. In calcareous soils it has been said to form hydroxyapatite. From a study of the reversion of mixtures of superphosphate and liming materials, MacIntire and his associates have recently suggested that the ultimate form of some of the phosphate applied to heavily limed soils may be fluorapatite; but, so far as we have been able to ascertain, no direct evidence has ever been obtained of the actual presence in the soil of apatite formed from fertilizers. diunduh dari: ….

53 A Simple Model to Describe the Dissolution of Phosphate Rock in Soils A. D. Mackay, J. K. Syers, R. W. Tillman and P. E. H. Gregg SSSAJ Vol. 50 No. 2, p Published: Mar, 1986 Dissolution of phosphate rock (PR) in contrasting soils was evaluated by extraction with 0.5 M NaOH following a prewash with 1 M NaCl to remove exchangeable Ca 2+. This provides a simple and direct method for measuring the rate and extent of PR dissolution in soils. Dissolution of Sechura phosphate rock (SPR) in six soils was essentially complete at 90 d and the pattern of dissolution could be described by a modified Mitscherlich equation of the form y = A (1 − e -ex ), in which y = amount of SPR dissolved at time x; A = asymptote, and c = curvature coefficient. Whereas A varied markedly across soils, c was independent of soil type. This exponential equation formed the basis of a simple model which describes and predicts the dissolution of SPR in soils. By establishing the relationship between A and a range of properties for 30 contrasting soils it was possible to identify those soil parameters that controlled PR dissolution in soil. Percent Ca-saturation, P-sorption capacity, and Ca- exchange capacity of the soil were the three most important parameters influencing SPR dissolution in soils. When a model incorporating these three parameters was tested on soils not used to construct the model, the variance accounted for ranged from 66 to 76%, depending on the population of soils selected. These parameters determine the concentrations of Ca 2+ and H 2 PO - 4 in the soil solution. diunduh dari: ….. https://www.soils.org/publications/sssaj/abstracts/50/2/SS

54 A Validation Test of a Field-Based Phosphate Analysis Technique Victor Bjelajac, Edward Luby, Rose Ray Journal of Archaeological Science. Volume 23, Issue 2, March 1996, Pages 243–248Volume 23, Issue 2 diunduh dari: ….. In this report, we evaluate a modified version of Eidt ’s (1973) field-based phosphate analysis technique to explore its validity. Soil samples were collected and analysed from an archaeological site in the Sunol Valley, Alameda County, California. Four characteristics were recorded for all soil samples. To evaluate the technique statistically, a ranking method was developed for each character and phosphate values were calculated. Based on site boundaries established by other archaeological techniques, including survey and mechanical subsurface testing, these phosphate values were designated as either “on-site ” or “off-site ”. Discriminant function analysis was then used to determine whether the phosphate values could be used reliably to classify sample locations. A valid threshold phosphate value, which we believe is predictive for other archaeological sites in the immediate geologic region, was developed for the Sunol Valley site. We suggest that once a minimum “site ” value for phosphate is established in a region, Eidt ’s modified technique can be used to identify areas of prior human occupation. In field situations where vegetation is dense and surface visibility is poor, this technique can offer a quick and inexpensive assessment of soil and site presence when other investigative approaches are not feasible.

55 . Phosphorus movement through soils and groundwater: Application of a time- dependent sorption model Goen E. Ho, Suprihanto Notodarmojo Water Science and Technology. Volume 31, Issue 9, 1995, Pages 83–90Volume 31, Issue 9 diunduh dari: ….. Pollution of groundwater, wetlands, rivers, estuaries and near shore waters by phosphorus is now fairly common due to run-off from agricultrual areas and wastewater discharges. In the application of fertilisers in agriculture it has been observed that sandy soils result in high phosphorus concentrations in the run-off. On the other hand loamy soils result in less phosphorus run-off. Phosphate-phosphorus sorption by soils has been observed to be time dependent. A model has been developed to describe the movement of phosphorus through soils to take into account the processes of convection, dispersion and time-dependent sorption. The model enables prediction of phosphorus breakthrough in a soil column. A comparison is made of predicted breakthrough curves with results obtained using two types of soil: a sandy soil from Australia and a loamy soil from Indonesia. The model has direct application to field situations where phosphate-phosphorus moves vertically downward through the unsaturated zone to the water table, and horizontally through the groundwater aquifer. Parameters of the model can potentially be derived from simple batch sorption experiments.

56 . Adsorption of phosphate on variable charge minerals and soils as affected by organic and inorganic ligands Developments in Soil Science, Volume 28, Part A, 2002, Pages A. Violante, M. Pigna, M. Ricciardella, L. Gianfreda diunduh dari: … &_sort=r&_st=13&view=c&_acct=C &_version=1&_urlVersion=0&_userid=10&md5=224dcd904b9d004a1df68f25a4f15b9f &searchtype=a. Metal oxides, noncrystalline or short-range ordered iron and aluminum hydroxides, poorly crystalline aluminosilicates, which are found within a wide range of soil orders, as well as organo-mineral complexes, are responsible for phosphate retention in soil environments. Strongly chelating organic acids produced by microorganisms or by plants (i.e., root exudates), as well as humic and fulvic acids, may strongly influence the adsorption of phosphate and its availability for plants. Maximum reduction in phosphate adsorption occurs when organic ligands are previously adsorbed on variable charge minerals or soils. The competitive adsorption of phosphate and organic ligands (e.g., oxalate, tartrate, malate, citrate) is influenced by pH, the nature of the ligands, and the nature of the surfaces of clay minerals and soils. Organic ligands may coprecipitate with OH-Al or OH-Fe species, forming organo-mineral complexes, which differ in chemical composition, surface properties, and reactivity toward phosphate. Nutrients and pollutants also compete with phosphate for the sorption sites of soil constituents. Sulfate inhibits phosphate adsorption or is not completely removed from the surfaces on which it is previously adsorbed only at low pH values. However, sulfate present in hydroxy-Al sulfate complexes is only partially removed even by large amounts of phosphate. Arsenate strongly competes with phosphate, but its efficiency in inhibiting phosphate adsorption is influenced by pH, concentration, order of anion addition, and nature of the surface of clay minerals and soils.

57 Managing Phosphorus for Crop Production Penn state Extension - Crop Management Extension Group- diunduh dari: …. Soil supply The soil solution is the key to plant nutrition because all phosphorus that is taken up by plants comes from phosphorus dissolved in the soil solution. Because the amount of soluble phosphorus in the soil solution is very low, it must be replenished by as many as 500 times during a growing season to meet the nutritional needs of a typical crop. Although very little phosphorus is in the soil solution at any time, there is a large amount of phosphorus in most soils. The bulk of the soil phosphorus is either in the soil organic matter or in the soil minerals. A large proportion of the phosphorus in both of these fractions is in very stable, unavailable forms, while a much smaller proportion is in available forms that can dissolve in the soil solution and be taken up by plants. The dynamic and available phosphorus phosphorus in these fractions, such as phosphorus added in fertilizer or manure, can be quickly fixed into stable, unavailable forms in the soil. This is why, even with optimum management, the efficiency of plant uptake of phosphorus is very low—usually less than 20 percent. At the same time as the soil solution phosphorus is depleted by crop uptake, unavailable phosphorus can slowly be released to more available forms to replenish the soil solution. This slow release can sustain plant growth in many natural systems, but is usually not rapid enough to maintain adequate phosphorus availability in intensively managed cropping systems without some supplemental phosphorus in the form of fertilizer, manure, or crop residues.

58 Managing Phosphorus for Crop Production Penn state Extension - Crop Management Extension Group- diunduh dari: …. Organic phosphorus availability depends on microbial activity to breakdown the organic matter and release this phosphorus into available forms. Thus, availability of organic phosphorus is very dependent on conditions in the soil and on the weather, which influence microbial activity. The mineralization of organic phosphorus to inorganic forms is favored by optimum soil pH and nutrient levels, good soil physical properties, and warm moist conditions. The inorganic phosphorus is bound with varying adhesiveness to iron and aluminum compounds in the soil. Replenishment of the soil solution with phosphate from inorganic forms comes from slow dissolution of these minerals. The solubilities of the compounds holding phosphorus are directly related to the soil pH. The pH range of greatest phosphorus availability is 6.0 to 7.0. At a lower pH, when the soil is very acidic, more iron and aluminum are available to form insoluble phosphate compounds and, therefore, less phosphate is available. At very high pH, phosphorus can react with excess calcium to also form unavailable compounds in the soil.

59 Managing Phosphorus for Crop Production Penn state Extension - Crop Management Extension Group- diunduh dari: …. Crop P Uptake Crop response to phosphorus depends on the availability of phosphorus in the soil solution and the ability of the crop to take up phosphorus. The availability of phosphorus in the soil solution has already been discussed. The ability of a plant to take up phosphorus is largely due to its root distribution relative to phosphorus location in soil. Because phosphorus is very immobile in the soil, it does not move very far in the soil to get to the roots. Diffusion to the root is only about 1/8 of an inch per year, and relatively little phosphorus in soil is within that distance of a root. Thus, the roots must grow through the soil and basically go get the phosphorus the plant needs. Therefore root growth is very important to phosphorus nutrition. Any factor that affects root growth will affect the ability of plant to explore more soil and get adequate phosphorus. Soil compaction, herbicide root injury, and insects feeding on roots can all dramatically reduce the ability of the plant to get adequate phosphorus. Young seedlings can suffer from phosphorus deficiency even in soils with high available phosphorus levels because they have very limited root systems that are growing very slowly in cold, wet, early early- season soil conditions. This is why some crops respond to phosphorus applied at planting in starter fertilizers even in relatively high phosphorus soils.

60 Managing Phosphorus for Crop Production Penn state Extension - Crop Management Extension Group- diunduh dari: …. Soil P-Test The most important tool in phosphorus management for crops is a soil test. Soil testing reveals soil pH, the soil phosphorus level, and determines the recommended application amount of phosphorus for the crop to be grown. There is no specific "available" fraction of phosphorus in soils. The available phosphorus is what is in solution plus what can be expected to become soluble from minerals and organic matter over the growing season. Therefore, soil tests cannot extract the exact available amount from the soil, but rather an amount that reflects what might become available. Research on Pennsylvania soils is then used to interpret the amount extracted by the soil test in terms of what is required for optimum crop production. This research has shown that on our soils, if the Mehlich 3 soil test used, in Pennsylvania extracts between 30 and 50 parts per million (ppm) phosphorus it is optimum for production of agronomic crops. Below 30 ppm phosphorus, additional phosphorus must be applied to build up the soil for optimum crop production. Above 50 ppm phosphorus, there will be no benefit to adding additional phosphorus. In some cases, applying a small amount of phosphorus as a starter on soils testing above 50 ppm may be beneficial. In the optimum range range—between 30 and 50 ppm phosphorus—phosphorus is often recommended to offset crop removal and thus maintain the soil in the optimum range over time.

61 Macroscale Chemical Properties and X-Ray Absorption Spectroscopy of Soil Phosphorus Dean Hesterberg. Developments in Soil Science. Volume 34, 2010, Pages 313–356Volume 34 diunduh dari: ….. Agricultural management strives to optimize phosphorus (P) nutrition of plants with minimal environmental impacts. Although most research on soil phosphorus has applied macroscale approaches, synchrotron X-ray absorption spectroscopy (XAS) is emerging as a nondestructive analytical technique for identifying phosphorus species in soils. The objective of this chapter is to convey the complementary nature of knowledge about soil phosphorus chemistry derived from various macroscale research approaches and XAS. A wealth of knowledge exists on phosphate sorption properties of soils and minerals. A limited number of XAS studies on soils have shown that multiple species of phosphate coexist, with Ca-phosphate minerals and phosphate sorbed to Fe- and Al-oxides commonly found in both acidic and calcareous soils. XAS analysis of phosphate associated with model soil matrix components provides more specific information on molecular bonding mechanisms. Such studies help to explain the behavior of P in soils and model systems, and they support mechanistic models for predicting long-term transformations, lability, and mobility of soil P.

62 Macroscale Chemical Properties and X-Ray Absorption Spectroscopy of Soil Phosphorus Dean Hesterberg. Developments in Soil Science. Volume 34, 2010, Pages 313–356Volume 34 diunduh dari: ….. Schematic of phosphorus cycling in an agricultural soil under crop production, including soil inputs, solid-solution equilibria, organic-inorganic P transformations, and loss pathways. To illustrate the dominance of P in soil solids, approximate fractions of total soil P (P t ) in various amendments, exports, and soil pools are shown. These fractions are based on an average P concentration of 800 mg/kg in the top 50 cm of soil (see text for details). (H n PO 4 n−3, n = 1 or 2, typically).

63 Macroscale Chemical Properties and X-Ray Absorption Spectroscopy of Soil Phosphorus Dean Hesterberg. Developments in Soil Science. Volume 34, 2010, Pages 313–356Volume 34 diunduh dari: ….. Comparison of a lability model (based on Olsen and Khasawneh, 1980) and a chemical speciation model for soil phosphorus.Olsen and Khasawneh, 1980 The speciation model includes multiple, hypothesized species along a continuum of lability, with lability varying with soil chemical conditions as illustrated for pH.

64 Macroscale Chemical Properties and X-Ray Absorption Spectroscopy of Soil Phosphorus Dean Hesterberg. Developments in Soil Science. Volume 34, 2010, Pages 313–356Volume 34 diunduh dari: ….. Solubility of selected Ca-, Al-, and Fe-phosphate minerals predicted by thermodynamics for equilibrium conditions in soils when Ca 2+ activity is 10 −2.5 or is fixed by calcite with partial pressure of CO 2 (g) = atm (revised from Lindsay, 1979, with permisson from the author).Lindsay, 1979

65 Macroscale Chemical Properties and X-Ray Absorption Spectroscopy of Soil Phosphorus Dean Hesterberg. Developments in Soil Science. Volume 34, 2010, Pages 313–356Volume 34 diunduh dari: ….. Sorption isotherms for phosphate on noncrystallines (non-xls) Al- hydroxide, ferrihydrite, and a 1:1 (mass) mixture of these minerals at pH 6; along with Freundlich models (solid lines) fit to the data. The dashed line is a model derived as a weighted combination of Freundlich models from the single- mineral systems, and represents how the mineral mixture would sorb phosphate if the system behaved as a linear combination of the individual minerals (q i = sorbed P and c i = dissolved P in the models; where i = A for Al-hydroxide, F for ferrihydrite, and M for the mixture) (from Khare et al., 2005 with permission).Khare et al., 2005

66 Macroscale Chemical Properties and X-Ray Absorption Spectroscopy of Soil Phosphorus Dean Hesterberg. Developments in Soil Science. Volume 34, 2010, Pages 313–356Volume 34 diunduh dari: ….. Phosphate sorption capacities of selected phyllosilicates and oxide minerals as a function of surface area determined by the BET (Brunauer- Emmett-Teller) method (data from Violante and Pigna, 2002). The quadratic regression model is fit to the data at pH 5. Violante and Pigna, 2002

67 Macroscale Chemical Properties and X-Ray Absorption Spectroscopy of Soil Phosphorus Dean Hesterberg. Developments in Soil Science. Volume 34, 2010, Pages 313–356Volume 34 diunduh dari: ….. Illustration of ternary phosphate complexes to soil organic matter through bridging Fe(III) and Al(III) ions, and a bidentate-binuclear bonded surface complex of (adsorbed) phosphate on an oxide mineral surface

68 Macroscale Chemical Properties and X-Ray Absorption Spectroscopy of Soil Phosphorus Dean Hesterberg. Developments in Soil Science. Volume 34, 2010, Pages 313–356Volume 34 diunduh dari: ….. Normalized phosphorus K-edge XANES spectrum and derivative XANES spectrum for variscite (AlPO 4 ·2H 2 O), showing spectral features attributable to bound states and continuum states.

69 diunduh dari: ….. _soil_phosphorus.php. Phosphorus cycle in agricultural soils.

70 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.

71 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. 6.


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