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Slide1
BAHAN KAJIAN
MK. DASAR ILMU TANAH
FOSFAT TANAH
www.marno.lecture.ub.ac.id
Slide2diunduh dari: ….. http://www.biocyclopedia.com/index/plant_nutrition/essential_elements_macronutrients/phosphorus/nature_and_transformations_of_soil_phosphorus.php
SIKLUS P DALAM TANAH PERTANIAN
Serapan
Tanaman
P-organik
P- pupuk
P- mineral
P- larutan
P- terserap
Pencucian & Runoff
sorpsi
desorpsi
pengendapan
pelarutan
mineralisasi
imobilisasi
Slide3Problematik Fosfor
Jumlah sedikit yang terdapat dalam tanah
Ketidak-tersediaan fosfor yg sdh ada dalam tanah
Adanya
fiksasi
fosfor
yang
menyolok
Slide4HUBUNGAN 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
Slide5Senyawa P dalam tanah
Senyawa P an-organik1. Senyawa Kalsium2. Senyawa besi dan aluminiumSenyawa Rumus KelarutanFluor-apatit 3 Ca3(PO4)2.CaFKarbonato-apatit 3 Ca3(PO4)2.CaCO3Hidroksi-apatit 3 Ca3(PO4)2.Ca(OH)2Oksi-apatit 3 Ca3(PO4)2.CaOTrikalsium-fosfat Ca3(PO4)2Dikalsium-fosfat CaHPO4 naikMonokalsium-fosfat Ca(H2PO4)2
Senyawa P-organik:
1. Fitin dan derivatifnya
2. Asam Nukleat
3. Fosfolipida
Slide6Fosfat 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
Slide7Fiksasi 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
Slide8Reaksi-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
)
Slide9Senyawa P-anorganik (mengendap)
Tanah-
tanah
masam
8
Fe
dan
Al
fosfat
FePO
4
l
2H
2
O, AlPO
4
l
2H
2
O
Tanah-
tanah
Alkaline
4
Ca
dan
Mg
fosfat
Slide10â Ca(H2PO4)2 â monocalcium phosphate â CaHPO4 â dicalcium phosphate â Ca3(PO4)2 â tricalcium phosphate â 3Ca3(PO4)2lCa(OH)2 â hidroksi-apatit â 3Ca3(PO4)2lCaCO3 â Apatite karbonat
Kelarutan menurun
Senyawa P-anorganik
pH
6
8
Slide11Tata-nama anion fosfat
H
3
PO
4
= phosphoric acid
H
2
PO
4
-
= monobasic
HPO
4
-2
= dibasic
PO
4
-3
=
tribasic
Slide12Fosfat paling tersedia pada kisaran pH 6 - 7
Oksida
hidrous
Slide13P-Organik dalam tanah
* Sekitar 20 - 80 % dari P-total dalam tanah berupa P-organik* Kebanyakan berupa fosfat-inositol, C6H6(OH)6 - sekitar 10 - 50 % dari P-organik - sebagian asam nukleat dan fosfolipid
Salah
satu
bentuk
P-
organik
dalam
tanah
adalah
inositol-hexaphosphate
,
jumlahnya
dapat
mencapay
50 %
dari
total P-
organik
dalam
tanah
.
Slide14P-Organik
(P-tersedia)
Siklus : Mekanisme pelepasan lambat
H
xPO4x-3
mineralisasi
imobilisasi
Fase
fosfat padatan
(
tidak-tersedia
)
Slide15HUBUNGAN SIMBIOSIS :Fungi dan Tumbuhan
Infeksi mikorhiza akar, kunci penyerapan fosfat
Hifa
fungi
Mikorhiza
Akar
tumbuhan
Slide16Reaksi 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
)
2
+ 3 CO
2
+ 5 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
Slide17acid soils
alkaline
soils
Dinamika
ion
fosfat
:
Protonasi
Slide18Ketersediaan P anorganik dalam tanah
Kemasaman tanah (pH):Ketersediaan P bagi tanaman tgt pd bentuk anion fosfat, selanjutnya bentuk anion ini tgt pada pH + OH- +OH- H2PO4- H2O + HPO4= H2O + PO4---larutan tanah larutan tanahsangat masam sangat alkalin
% kepekatan
100 50 H3PO4 H2PO4- HPO4= PO3-3 0 0 2 4 6 8 10 12 14 pH larutan
Paling tersedia bagi tanaman
Slide19Ketersediaan P-anorganik tanah masam
Pengendapan oleh kation Fe, Al, Mn Al3+ + H2PO4- + H2O 2H+ + Al(OH)2H2PO4 larut tdk larutDlm tanah masam biasanya konsentrasi kation Fe, Al lebih besar dp anion fosfat, sehingga reaksi berlangsung ke arah kanan
Pengikatan oleh hidro-oksida: Fiksasi fosfat
OH OH
Al OH + H2PO4- OH- + Al OH OH larut H2PO4 tdk larutHidro-oksida Al
Pengikatan oleh liat silikat: Kaolinit, Montmorilonit, 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 silikat
tidak larut
Slide20Ketersediaan P-anorganik pd pH tinggi
Pengendapan oleh kation Ca++ atau CaCO3 H2PO4- + 2 Ca++ Ca3(PO4)2 + 4H+ larut tidak larut H2PO4- + 2 CaCO3 Ca3(PO4)2 + 2CO2 + 2H2O larut tidak larut
Ca
3(PO4)2 yang terbentuk dalam reaksi di atas, masih dapat berubah menjadi bentuk-bentuk yang lebih sukar larut, seperti senyawa hidroksi-, oksi- , karbonat-, atau fluor-apatit.Reaksi-reaksi ini semua terjadi pada tanah-tanah masam yang dikapur dengan dosis tinggi (Pengapuran berat)
Slide21Daya 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)2Tidak larut: CaHPO4 dan Ca3(PO4)2
Slide22Kemampuan tanah menjerap (Daya Jerap) P
Tanah Mineral Liat Perlakuan pH Daya Jerap P (*) Latosol - Tanpa kapur 5.7 30.110 Purwokerto Haloisit Dengan kapur 5.9 26.600 Latosol- Kaolinit Tanpa kapur 5.2 45.520Cibodas Dengan kapur 5.6 40.920Podsolik- Smektit Tanpa kapur 4.8 36.950Gajrug Dengan kapur 5.3 33.180Podsolik- Smektit Tanpa kapur 4.6 29.280Samarinda Kaolinit Dengan kapur 5.2 16.370Grumusol- Smektit, Kaolinit Tanpa kapur 6.7 14.960Yogjakarta HaloisitAndosol Bogor Alofan, Haloisit Tanpa kapur 4.6 33.360
Keterangan: (*) setara dengan kg superfosfat 20% P2O5 setiap HLO
Pengapuran setara dengan 0.5 SMP
Sumber: Djokosudardjo (1982)
Slide23Pengelolaan 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 buatan
Mineral tanah
BOT
Tanaman
Pencucian
Fiksasi
Erosi
Slide24Siklus 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)
Slide25P- tanah
P-anorganik:1. Fraksi aktif: Al-P, Fe-P dan Ca-P2. Fraksi tidak aktif: P-terjerap (P-absorption) P-terselimuti (P-occluded)
P-organik
1. Inositol fosfat, Fosfolipid, Asam nukleat, Nukleotida, Gula-fosfat2. P-organik menyumbang 30-50% dari P-total tanah3. Senyawa P-organik terdapat dalam humus dan tubuh jasad tanah4. P-organik dalam tanah berasal dari bahan organik
Penambahan bahan organik ke tanah bertujuan:
1. Meningkatkan kandungan bahan organik 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.
Slide261. No direct practical importance2. Sering dipakai sbg “Indeks Pelapukan”3. P-total topsoil menurun dengan intensitas pelapukan4. Tanah-tanah tropis mengandung sekitar 200 ppm5. Ultisol & Alfisol : < 200 ppm P6. Andepts umumnya 1000 - 3000 ppm P7. Vertisol umumnya 20 - 90 ppm P8. Entisol & Inceptisols: beragam p-totalnya9. Oxisols umumnya < 200 ppm P10. …..
TOTAL P - TANAH
Slide271. P-organik = 20-50 % total P-tanah2. Oxisols, Ultisols, Alfisols: P-organik = 60-80% P-total3. C:P rasio dalam tanah = 240:1 -- 110:14. N:P rasio dlm tanah = 20:1 -- 9:15. Mineralisasi P-organik sukar diukur, karena ion H2PO4- yg dilepaskan ke tanah dengan cepat difiksasi menjadi bentuk-bentuk P-anorganik6. Pemupukan N dan P mempercepat mineralisasi P-organik7. P-organik dlm tanah menjadi sumber P yg penting bagi tanaman kalau tidak ada pemupukan P.
FOSFAT ORGANIK
Slide28BAHAN ORGANIK SUMBER P
Komponen kualitas bahan organik sebagai sumberP: 1. Nisbah C/N (nilai kritisnya 25-30)2. Nisbah C/P ( < 200: mineralisasi P > 300 : imobilisasi P) 3. P-total4. Kandungan lignin dan polifenol5. Kapasitas polifenol mengikat protein 6. Indeks jangka-pendek pupuk hijau: C/N, kandungan lignin dan polifenol
1. Kandungan lignin dan polifenol yang rendah mempercepat laju mineralisasi P
2. Bahan organik dengan kandungan P lebih dari 2500 ppm akan terjadi mineralisasi P dan menurunkan jerapan P-tanah3. Lignin merupakan senyawa polimer pd jaringan tanaman berkayu, sulit dirombak oleh mikroba tanah
Polifenol merupakan senyawa aromatik-hidroksil :
a. Polifenol larut air & Polifenol tdk larut 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
Slide291. P - ANORGANIK: Fraksi aktif & Fraksi tidak aktif2. Fraksi aktif : Ca-P, Al-P dan Fe-P3. Fraksi tdak-aktif : Occluded-P dan Reductant-soluble P4. Occluded-P : senyawa Fe-P dan Al-P yang dibungkus oleh selubung inert.5. Rs-P : Senyawa P yg dibungkus oleh selubung dari bahan yang dpt larut pd kondisi anaerobik6. Transformasi bentuk-bentuk P-tanah dikendalikan pH7. Ca-P lebih mudah larut dp Fe-P dan Al-P8. Rezim air sgt berpengaruh thd transformasi P-tanah 9. Kondisi AQUIK ---- Akumulasi Al-P10. Kondisi USTIK ------ Akumulasi Fe-P
P - ANORGANIK
Slide30Faktor Retensi P dalam tanah
TIPE LIAT Tanah-tanah liat lebih banyak meretensi & memfiksasi p-pupuk daripada tanah berpasirLiat silikat tipe 1:1 mempunyai kemampuan lebih besar me-”retensi” P dibanding liat tipe 2:1Tanah yang kaya liat kaolinitik akan “mengikat” lebih banyak P -pupuk daripada tanah yang kaya liat tipe 2:1Adanya liat oksida hidrous dari Fe dan Al juga terlibat dalam retensi P-pupuk
TIME OF 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 PImplikasi 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? …………
Slide31Faktor Retensi P dalam tanah
pH TANAH Kisaran pH tanah yg optimum bagi ketersediaan p-tanah adalah 5.5 - 7.0Pd tanah dg pH rendah, retensi terjadi karena adanya reaksi fosfat dengan Fe, Al dan oksida hidratnya.Pd tanah dg pH tinggi, retensi fosfat terjadi karena reaksi fosfat dengan Ca dan Mg dan karbonatnya
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
…………………………..
Slide32Faktor Retensi P dalam tanah
BAHAN ORGANIK Lanjutan ……. Dekomposisi bahan organik menghasilkan anion-anion yang mampu membentuk senyawa kompleks dengan Fe dan Al, sehingga kation-kation ini tidak bereaksi dengan fosfatAnion-anion organik ini juga mampu melepaskan fosfat yang difiksasi oleh Fe dan AlAnion-anion yang efektif menggantikan fosfat tsb adalah sitrat, oksalat, tartrat, malat, dan malonat.
STATUS FOSFOR dalam 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
…………………..
Slide33Fiksasi P-pupuk , % 100 80 60 40 20 Pasio R2O3 : P2O5
FIKSASI P vs R2O3 : P2O5
Slide341. 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 soluble3. Pada tanah alkalis: Ca-P dan Mg-P yg insoluble4. Pd tnh masam: Fe-P dan Al-P yg insoluble5. Al+++ + mono-kalsium fosfat ------ Al(OH)2H2PO4 (liming with phosphorus)6. Kapasitas fiksasi P = F(oksida Fe dan Al; Aldd)7. Intensitas Fiksasi P: Oksida > Oksida > Liat 1:1 > Liat 2:1 amorf kristalin
PROSES FIKSASI P-TANAH
Slide35Tanah Liat dominan % Liat Fixed P (ppm) Adsorpsi Max. Pd 0.2 ppm P lrt tnhInceptisol Montmorilonit 27 106 83Ultisol Kaolinit 38 480 360Oxisol Kaolinit 36 531 395Andept Alofan 11 1050 670Sumber: NCSU, 1973
BESARNYA FIKSASI P-TANAH
Slide361. H2PO4- dlm larutan tanah < 10 ppm, dlm tanaman 2000 ppm2. 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 saat4. Mineralogi liat tanah sgt menentukan kapasitas fiksasi P5. Liat oksida & Alofan > Kaolinit > Montmorilonit6. Uji tanah untuk P : mengekstraks sejumlah P-tersedia dlm tanah yg berkorelasi dg respon tanmn thd pemupukan P7. Tingkat kritis hasil uji tanah sekitar 0.07 - 0.2 ppm P dlm larutan tanah
PELEPASAN P-TANAH
Slide37REAKSI P tanah ALKALINE
PRESIPITASI DIKALSIUM FOSFAT Pada kondisi Ph tanah yang tinggi dan kaya kalsium, terjadi pengendapan senyawa-senyawa:1. Kalsium fosfat: Ca3(PO4)2; CaHPO42. Hidroksi-apatit3. Karbonat-apatit
PRESIPITASI PERMUKAAN PADATAN KALSIUM KARBONAT
Ion-ion fosfat yang kontak dengan permukaan padatan kalsium karbonat akan diendapkan pd permukaan partikel ini. Hasil akhir dari reaksi ini adalah garam-garam tidak larut dari kalsium, fosfat, dan mungkin 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
…………………..
Slide38P-aded (ppm) 1200 1000 800 600 400 200 0.001 0.01 0.05 0.1 0.2 1.0 P dlm larutan tanah, ppm
P-FIXATION ISOTHERMS
Oxisol, 45% liat
Andept
Ultisol , 38% liat
Tnh Montmorilonit, 40% liat
Sumber: Fox, 1974
Slide39Tanaman Hasil, t/ha P-removal, kg/ha1. Jagung Biji : 1.0 6 Jerami : 1.5 3 Biji : 7.0 20 Jerami : 7.0 142. Padi Biji : 1.5 7 Jerami : 1.5 1 Biji : 8.0 32 Jerami : 8.0 53. Nanas Buah : 12.5 2.3 4. Tebu 2 th Above ground: 100 20 300 35Sumber: Sanchez, 1976.
KEBUTUHAN TANAMAN
Slide40Hasil relatif (%) 100 80 60 40 20 0.003 0.006 0.050 0.100 0.200 0.400 1.600 P- larutan tanah, ppm
RESPON TANAMAN thd P-TANAH
Ubijalar: toleran tanah miskin P
Jagung: intermediate
Lettuce: In-tolerant
Slide41Tanaman P-larutan tnh yg menghasilkan 95% hasil maks., ppm1. Lettuce 0.402. Tomat 0.253. Cucumber 0.204. Kedelai (vegetable) 0.205. Ubijalar 0.106. Jagung 0.607. Sorghum 0.508. Kubis 0.04Sumber: Fox et al. (1974)
TINGKAT KRITIS P-TANAH
Slide42Tanaman Internal P Requirement, %P 1. Stylosanthes humilis 0.172. Centrosema pubescens 0.163. Desmodium intortum 0.224. Digitaria decumbens 0.165. Panicum maximum 0.196. Pennisetum clandestinum 0.227. Paspalum dilatatum 0.258. Sumber: Andrew & Robins (1969, 1971)
TINGKAT KRITIS P-TANAMAN
Slide43TEKNOLOGI PEMUPUKAN FOSFAT :1. Respon pupuk P sgt tinggi pada Oxisol, Ultisol, andepts, Vertisols2. Dosis pupuk P = F (jenis tanaman, tanah, cara aplikasi, musim)3. Dosis Rekomendasi Jagung, kedelai, Tebu: 100 - 150 kg P2O5/ha4. Kapasistas fiksasi P tanah menentukan cara aplikasi pupuk P: Disebar, ditugal, digarit, pd lubang tanam, dll5. Pada tanah yg memfiksasi P ada dua strategi: 1. Dosis medium, digarit, setiap musim tanam 2. Dosis tinggi unt menjenuhi kapasitas fiksasi P-tanah, dan efek residunya berlangsung beberapa tahun6. Pupuk P yg baik harus mengandung 40-50 % P dlm bentuk larut air , untuk memenuhi kenbutuhan awal pertumbuhan tanaman7. Aplikasi kapur & silikat mampu menurunkan fiksasi P dlm tanah8. Pengapuran hingga pH 5.5 - 6.0 umumnya meningkatkan ketersediaan P dalam tanah, mengurangi fiksasi P
PEMUPUKAN FOSFAT
Slide44Hasil biomasa , % 100 80 60 40 20 0 115 230 460 Pemupukan P (ppm P) Sumber: Mendez-Lay (1974), Tnh Oxisol.
EFEK PENGAPURAN THD FIKSASI P
Tingkat kritis
Tdk dipakur pH= 4.8
Dikapur hingga pH = 5.5
Slide45Kapasitas fiksasi P tanah sngt tinggi, alternatif pengelolaan:1. Kombinasi cara aplikasi pupuk P: ditugal/digarit dg sebar2. Batuan-fosfat larut sitrat3. Aplikasi kapur atau Ca-silikat unt ngurangi fiksasi P4. Kultivar tanaman yg toleran thd larutan tanah yg miskin fosfat5. Pertimbangan biaya pupuk & pemupukan.
PENGELOLAAN P TANAH MASAM
Slide46PERILAKU 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
…………………..
Slide47MONO KALSIUM FOSFAT
Granula Monokalsium fosfat: H2O H2O H2O
Consentrated medium, pH 1.5, dimana CaH2PO4 dan CaHPO4
bergerak ke luar
Melarutkan Fe, Al, dan Mn
Pembentukan besi-fosfat, Al-fosfat, Mn-fosfat yg mengendap
MnPO4
FePO4
AlPO4
Slide48NILAI 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.
Slide49NILAI 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.
Slide50MEKANISME 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
Slide51ABSORPSI & OKLUSI P-TANAH
Absorpsi P-terjerap ke dalam mineral tganah (a) dan Oklusi lebih lanjut P-terjerap b)
Diunduh dari: ……… 27/3/2013
Mineral
tanah
Mineral tanah
larutan tanah
P terjebak oleh selimut
Selimut
oksida
Fe
atau
Al
Slide52Dinamika P-tanah, termasuk tranformasi dan perilaku P dari pupuk fosfat.
Pergerakan P-tanah snagat terbatas, sehingga penempatan pupuk P dalam tanah snagat kritis dalam mencapai efisiensi serapannya. Banded applications of fertilizer P have proven the most effective thereby minimizing surface contact with the soil which tends to decrease the solubility of the applied P. Faktor lain yg berpengaruh adalah kesehatan tanaman, tdk ada penyakit, dan tanah yg hangat.
Diunduh dari: http://www.extension.org/pages/9873/phosphorus-p ……… 27/3/2013
PO4
terlarutLarutan Tanah
BO hidup ----- BO mati
Erosi tanah
Binatang
Tanaman
Tanaman
Pupuk kimia
PO4 terjerap
PO4 mengendapFe, Al, Ca
Mineral tanah
RabukKomposHumus
Sistem
Tanah
Slide53Diunduh dari: http://www.sciencedirect.com/science/article/pii/S0166248110340116 ……… 27/3/2013
SIKLUS P DALAM TANAH (Dean Hesterberg, 2010)
P-mineralCa-fosfatFe-fosfatAl-fosfat
P-terjerapP-teroklusiPO4-Fe-oksidaPO4-Al-oksidaPO4-Fe Al-BO
Residu P-organik(3% dari Pt)P-humus(15-60% dari Pt)
P-biomasa mikroba(0.4 – 7.5% dari Pt)
P biomasa tanaman(0.2-0.6% Pt bagian di atas tanah)
P-panen tanaman
Bahan pembenah(0.8-2.4% Pt (pupuk, rabuk, biosolid)
P-runoff (<0.15% Pt)
Terlarut
dan
partikulat
Slide54Bentuk-bentuk P yang ada dalam tanah.
P dalam tanah dapat dikelompokkan menjadi tiga “pool” yg berbeda tingkat ketersediaannya bagi tanaman. These pools are the readily available P (soil solution), the pool of P that is rapidly released from the soil to replenish the soil solution (labile pool), and the relatively slowly available P (non-labile)
Diunduh dari: http://www.grdc.com.au/Research-and-Development/GRDC-Update-Papers/2009/02/THE-SCIENCE-OF-PHOSPHORUS-NUTRITION-FORMS-IN-THE-SOIL-PLANT-UPTAKE-AND-PLANT-RESPONSE ……… 27/3/2013
P-
larutan
P-labil
P
Tidak
labil
Slide55(Sumber: Sharpley and Sheffield, Livestock and Poultry Environmental Stewardship Curriculum)
Diunduh dari: http://passel.unl.edu/pages/informationmodule.php?idinformationmodule=1118084123&topicorder=5&maxto=7 ……… 27/3/2013
SIKLUS P-TANAH
Panen Tanaman
Sisa panen
Aplikasi Pupuk P
Aplikasi P Rabuk
P-Anorganik
P-Organik
P- Uji Tanah
P-
larutan
Labil
Stabil
Labil
Stabil
Tanaman
Slide56Kesetimbangan P dalam tanah
Kalau P diserap ke dalam tanah setelah aplikasi pupuk, risiko kehilangan P-larut ke dlaam runoff akan semakin berkurang (menurun) dnegan waktu.(Sumber: Image courtesy of Charles Wortmann)
Diunduh dari: http://passel.unl.edu/pages/informationmodule.php?idinformationmodule=1118084123&topicorder=5&maxto=7 ……… 27/3/2013
P -
larutan
P - larutan
P - larutan
Stabil ---- Labil
Stabil ---- Labil
Stabil ---- Labil
P-rabuk sebagian besar P-labil + P-larutan
P-
rabuk
bereaksi
dnegan
bahan
organik
tanah
dan
senyawa-senyawa
Fe, Al
dan
Ca
fosfat
menjadi
kurang
tersedia
Slide57SIKLUS P DALAM TANAH
Diunduh dari: http://www.env.go.jp/en/wpaper/1995/eae240000000010.html ……… 27/3/2013
Tanaman
Akar
Tanaman
Sisa Tanaman
P larut air
Reaksi penjerapan (adsorpsi) asam fosfat
P-organik mudah lapuk
P-organik agak sukar lapuk
P-organik sukar lapuk
P-organik stabil bergabung dengan liat
Batuan fosfat
Asam fosfat dg Ca, Al, Fe
Oksida, dan asam fosfat dalam liat
SUMBER : "
Kikan
Kagaku-
sosetsu
, 4" (
Quaterly
Chemistry 4), Science Society of Japan, ed., "
Chemisory
of Soil"
Slide58Apakah P-tanah itu?
Phosphorus (P), unsur hara esensial bagi tanaman. Unsur hara ini sangat kritis karena konsentrasinya dalam tanah snagat rendah ( 600 ppm total P) dan kelarutannya snagat rendah (rata-rata 0.05 mg P L-1 dalam larutan tanah). Soil P exists in inorganic and organic forms. Inorganic forms are associated with amorphous and crystalline aluminium and iron compounds in acid soils and calcium compounds in alkaline soils. Bentuk-bentuk P-organik berhubungan dengan bahan organik dalam tanah.
Diunduh dari: http://www.gnb.ca/0173/30/0173300016-e.asp ……… 27/3/2013
Rabuk
Pupuk
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
:
Slide59Options for managing soil phosphorus supplyDr. Ann McNeillSchool 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; Impor P sebagai pupuk, yaitu pupuk mineral atau organik,Praktek untuk meningkatkan siklus P tanah untuk mendorong sinkronisasi pelepasan dan serapan P-tersedia oleh tanamanMemaksimumkan efisiensi pemanfaatan P oleh tanaman.
Diunduh
dari
: http://www.grasslands.org.au/resources/Articles/NewsletterArticle1.html ……… 27/3/2013
Slide60Options for managing soil phosphorus supplyDr. Ann McNeillSchool of Earth & Environmental Sciences, University of Adelaide, South Australia. 21st July 2008
Diunduh dari: http://www.grasslands.org.au/resources/Articles/NewsletterArticle1.html ……… 27/3/2013
Soil P cycle - pools and pathways. Modified from [McLaughlin et al. 1999, 1]
Cadangan
biomasa mikroba
Po Labil
Po tidak-LabilFASE ORGANIK
Pi dapat ditukar
Pi tidak-dapat ditukarMINERAL
CADANGAN LARUTAN TANAHP -Organik + anorganik
Pertukaran kontak
Adsorpsi
Desorpsi
Pengendapan
Asimilasi
Dekomposisi BO
Mineralisasi Non-asimilatory
Mineralisasi
Imobilisasi
Penyerapan akar
ekskresi
akar
Slide61The value of phosphorus in crop stubbleSarah Noack1, Mike McLaughlin, Ron Smernik, Therese McBeath and Roger Armstrong 1The University of Adelaide
Phosphorus within the stubble can be released directly to soil as soluble P (where it can be used immediately by the crop or chemically fixed onto the soil) atauDiserap oleh mikroba dan selanjutnya dilepaskan kembali ke tanah dalam waktu mendatang.
Diunduh dari: http://www.grdc.com.au/Research-and-Development/GRDC-Update-Papers/2012/02/The-value-of-phosphorus-in-crop-stubble ……… 27/3/2013
P
mikroba
P labil
P larutan
P tdk tersedia
P dalamTanaman
P
dalam
Seresah
sisa
panen
Slide62KETERSEDIAAN P DALAM TANAH
Fosfat mudah diikat dna menjadi bagian dari senyawa kalsium, besi dan aluminum dalam tanah:Only 10 - 30% of phosphate fertilizer is used in the year it is applied1/3 to 1/2 of the phosphate (P) fertilizer applied may never be recoveredP is most available in soils with a neutral pH (it is quickly tied up with pHs above or below)Tanah-tanah yg kaya debu atau liat mengikat lebih banyak PSemakin rendah lengas tanah = semakin rendah ketersediaan PSemakin rendah suhu tanah = semakin rendah ketersediaan P
Diunduh
dari
: http://www.bioag.novozymes.com/en/products/canada/aboutphosphate/soil-phosphate/availability-in-cold-soils/Pages/default.aspx ……… 27/3/2013
Slide63KETERSEDIAAN P DALAM TANAH
P-larutan berbentuk ortofosfat. Molekul ini terdiri atas atom P (bulatan kuning) dikelilingi oleh empat atom oksigen (bulatan merah).
Diunduh dari: http://www.bioag.novozymes.com/en/products/canada/aboutphosphate/soil-phosphate/availability-in-cold-soils/Pages/default.aspx ……… 27/3/2013
P -
larutan
Ion ortofosfat sekunder:HPO4= (pH>7.0)
Ion ortofosfat primer:H2PO4- (pH<7.0)
Bentuk
yg
lazim
ditentukan
oleh
pH
tanah
,
kedua
bentuk
ion
seimbang
pd
kondisi
netral
Slide64Hubungan antara serapan P-tanaman dgn P-tersedia dalam tanah akibat aplikasi TSP dan PR ke tanah masam
When a water-soluble P fertilizer, e.g. TSP, is applied to acid soil containing oxides of iron (Fe) and aluminium (Al), reaction products in the form of Fe-Al-P are the sources of available P through desorption/dissolution processes for uptake by the plant. Kalau jumlah P yg terekstraks oleh uji tanah (k1’) seimbang (korelasinya kuat) dengan jumlah P yg diserap oleh tanaman (k1) atau hasil tanaman, maka uji tanah ini cocok untuk kalibrasi rekomendasi dosis pupuk berdasar P-larut air.
Diunduh dari: http://www.fao.org/docrep/007/y5053e/y5053e0b.htm ……… 27/3/2013
Slide65IKTISAR 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 tanaman2. 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.
Slide66IKTISAR FOSFAT - TANAH
6. Pupuk fosfat dapat diklasifikasikan berdasarkan proses pembuatannya, menjadi: Heat-processed phosphate, dan Acid-treated Phosphate.
7. Reaksi pupuk fosfat larut air dengan berbagai komponen tanah menghasilkan “produk reaksi pupuk - tanah”. Kelarutan hasil reaksi inilah yang menentukan ketersediaan fosfat bagi tanaman
8. Kandungan air tanah sangat menentukan efektifitas dan laju ketersediaan pupuk fosfat. Pada kondisi air tanah kapasitas lapangan sekitar 50-80 % fosfat larut air dapat bergerak ke luar dari granula pupuk dalam periode 24 jam.
Slide67UJI P-TANAH:
PRINSIP DAN ANALISISNYA
Slide68Soil Test Phosphorus: Principles and OverviewJ. Thomas Sims, University of Delaware
The fundamental goal of soil P testing has always been to identify the “optimum” soil test P concentration required for plant growth. The need for additional fertilization or manuring, and the economic return on an investment in fertilizer P, could then be predicted. Menurut Sims et al. (1998), tujuan lain dari uji P-tanah adalah : Menentukan “indeks” kapasitas tanah mensuplai P, shg dapat mengestimasi waktu sebelum melakukan pemupukan fosfat diperlukan lagi. Mengelompokkan tanah, dalam hal respon ekonomis terhadap pupuk P, berdasarkan sifat fisika dna kimia tanah, Mengidentifikasi apakah tanah berkelebihan P sehingga menjadi sumber pencemaran bagi perairan.
Diunduh
dari
: https://secure.hosting.vt.edu/...
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.../Methods_of_
P
_Analysis_2000.pd... ……… 27/3/2013
Slide69Soil Test Phosphorus: Principles and OverviewJ. Thomas Sims, University of Delaware
Menurut Bray (1948), uji P-tanah yg bermanfaat secara agronomis harus mempunyai karakteristik:Uji tanah harus mampu mengekstraks semua atau sebagian P-tersedia dalam tanah yang beragam sifat kimia dan mineralogisnya.Uji tanah harus akurat dan cepat.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.Uji tanah harus dapat secara akurat mendeteksi perbedaan konsnetrasi P-tanah akibat pemupukan sebelumnya.
Diunduh
dari
: https://secure.hosting.vt.edu/...
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.../Methods_of_
P
_Analysis_2000.pd... ……… 27/3/2013
Slide70Soil Test Phosphorus: Principles and OverviewJ. 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 10-15 hectares. These cores are then composited to produce one sample that is submitted to the laboratory for analysis. Soil sampling patterns should reflect natural differences in soils (e.g., soil series) and any management practices or historical activities likely to affect soil test results (e.g., crop rotation,
manuring
, tillage practice).
Sampel
tanah
:
Penanganan
dan
penyiapannya
Care should be taken during soil sample handling to avoid contamination from sampling and mixing devices. After collection, soil samples should be submitted as soon as possible to the laboratory where they are normally air-dried and ground or crushed to pass a 2mm sieve prior to analysis. Providing as much information as possible with the sample (e.g., previous fertilizer use, intended management plans, soil series) helps to ensure an accurate recommendation.
Slide71Soil Test Phosphorus: Principles and OverviewJ. 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 tanahDefinisi dan pertimbangan umumAnalisis sampel tanahFrom 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 analisisThe 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
.
Slide72Soil Test Phosphorus: Bray and Kurtz P-1J. Thomas Sims, University of Delaware
The Bray and Kurtz P-1 soil test phosphorus (P) method was developed by Roger H.Bray and Touby Kurtz of the Illinois Agricultural Experiment Station in 1945 and is now widely used in the Midwestern and North Central United States (Bray and Kurtz, 1945; Frank et al., 1998). Phosphorus extracted by the Bray and Kurtz P-1 method has been shown to be well-correlated with crop yield response on most acid and neutral soils in these regions. For acid soils, the fluoride in the Bray and Kurtz extractant enhances P release from aluminum phosphates by decreasing Al activity in solution through the formation of various Al-F complexes. Fluoride is also effective at suppressing the readsorption of solubilized P by soil colloids. The acidic nature of the extractant (pH 2.6) also contributes to dissolution of available P from Al, Ca, and Fe-bound forms in most soils. Uji tanah dnegan metode Bray tidak cocok untuk:Tanah-tanah liat yang kejenuhan basanya cukup tinggi,Tanah-tanah lempung-liat-berdebu atau yg lebih halus dengan pH tinggi atgau tanah berkapur (pH > 6.8) atau kejenuhan basanya tinggi,Tanah-tanah yang mempunyai kalsium karbonat setara > 7% kejenuhan basa, Tanah-tanah yang kaya kapur ( > 2% CaCO3).
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: https://secure.hosting.vt.edu/...
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.../Methods_of_
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_Analysis_2000.pd... ……… 27/3/2013
Slide73Soil Test Phosphorus: Bray and Kurtz P-1J. Thomas Sims, University of Delaware
In soils such as these, the acidity of the extracting solution can be neutralized unlessthe ratio of extractant:soil is increased considerably. Additionally, CaF2, formed from the reaction of soluble Ca+2 in the soil with F- added in the extractant, can react with and immobilize soil P. Both types of reactions reduce the efficiency of P extraction and result in low soil test P values. Pengekstraks Bray & Kurtz dapat melarutkan P dari batuan fosfat, sehingga tidak boleh dipakai pada tanah-tanah yang baru diberi bahan-bahan pembenah ini, karena akan mengakibatkan over-estimate P-tersedia.. Nilai-nilai P ( Bray & Kurtz P-1) sebesar 25 - 30 mg P/kg tanah seringkali dianggap optimum bagi pertumbuhan tanaman, meskipun Holford (1980) melaporkan nilai kritis yg lebih rendah untuk tanah-tanah yg daya buffernya tinggi.
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dari
: https://secure.hosting.vt.edu/...
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.../Methods_of_
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Slide74Soil Test Phosphorus: Bray and Kurtz P-1J. Thomas Sims, University of Delaware
Peralatan lab:Ayakan No. 10 (diameter lubang 2 mm)Standard 1 g and 2 g stainless steel soil scoopsAutomatic extractant dispenser, 25 mL capacityExtraction vessels, such as 50 mL Erlenmeyer flasks, and filter funnels (9 and 11 cm) and racksRotating or reciprocating shaker with a capability of 200 excursions per minute (epm)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.)
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Slide75Soil Test Phosphorus: Bray and Kurtz P-1J. Thomas Sims, University of Delaware
Reagen = Pereaksi:Bray and Kurtz P-1 Extracting Solution (0.025 M HCl in 0.03 M NH4F): Dissolve 11.11 g of reagent-grade ammonium fluoride (NH4F) in about 9 L of distilled water. Add 250 mL of previously standardized 1M HCl and make to 10 L volume with distilled water. Dicampur secara merata. pH larutan yg dihasilkan harus pH 2.6 ± 0.05. Penyesuaian pH dilakukan dnegan menggunakan HCl atau NH4OH. Simpan dalam polyethylene-carboys hingga saatnya digunakan.
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Slide76Soil Test Phosphorus: Bray and Kurtz P-1J. Thomas Sims, University of Delaware
Prosedur kerja :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.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 27oCIf 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.Menyaring ekstraks dengan Kertas saring Whatman No. 42. Ulangi kembali penyaringan kalau filtratnya belum jernih.Menganalisis P dengan colorimetry atau spectroscopy dengan menggunakan larutan blanko dan standar yang disiapkan dalam larutan pengekstraks Bray P-1.
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Slide77Soil Test Phosphorus: Bray and Kurtz P-1J. 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 ) =(CP x [0.020 L ekstraks] ) / 0.002 kg tanahdimana: CP = Konsentrasi P dalam ekstraks Bray & Kurtz P-1, mg/L .
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References:
Bray R.H., and L.T. Kurtz. 1945. Determination of total, organic and available forms of phosphorus in soils. Soil Sci. 59:39-45.
Frank, K.D.
Beegle
, and J. Denning. 1998. Phosphorus. p. 21-30. In J. R. Brown (ed.) Recommended Chemical Soil Test Procedures for the North Central Region. North Central Reg. Res. Publ. No. 221 (revised).
Holford
, I.C.R. 1980. Greenhouse evaluation of four phosphorus soil tests in relation to phosphate buffering and labile phosphate in soils. Soil Sci. Soc. Am. J. 44:555-559.
Slide78Soil Test Phosphorus: Olsen PJ. Thomas Sims, University of Delaware
The “Olsen P” or sodium bicarbonate soil test phosphorus (P) method was developedby Sterling R. Olsen and co-workers in 1954 (Olsen et al., 1954) to predict crop response to fertilizer P inputs on calcareous soils. It is primarily used in the North Central and western United States. Metode ekstraksi P-Olsen cocok untuk tanah-tanah berkapur, terutama yang mempunyai > 2% calcium carbonate, tetapi juga cukup efektif untuk tanah-tanah masam (Fixen and Grove, 1990). The method is based on the use of the HCO3-, CO3-3 and OH- in the pH 8.5, 0.5M NaHCO3 solution to decrease the solution concentrations of soluble Ca2 by precipitation as CaCO3 and soluble Al3+ and Fe+3 by formation of Al and Fe oxyhydroxides, thus increasing P solubility. Peningkatan muatan negatif permukaan dan/ atau penurunan jumlah tapak sorpsi pada permukaan oksida Fe dan Al pada kondisi pH tinggi juga memicu desorpsi P-tersedia ke dalam larutan.
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Slide79Soil Test Phosphorus: Olsen PJ. 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.
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Slide80Soil Test Phosphorus: Olsen PJ. Thomas Sims, University of Delaware
Peralatan Lab:Ayakan No. 10 (diameter lubang 2 mm)Standard 1 g and 2 g stainless steel soil scoopsAutomatic extractant dispenser, 25 mL capacityExtraction vessels, such as 50 mL Erlenmeyer flasks, and filter funnels (9 and 11 cm) and racksRotating or reciprocating shaker with a capability of 200 excursions per minute (epm)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.)
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Slide81Soil Test Phosphorus: Olsen PJ. 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.
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Slide82Soil Test Phosphorus: Olsen PJ. Thomas Sims, University of Delaware
Prosedur: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.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 270CIf 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.Filter extracts through Whatman No. 42 filter paper or through a similar grade of paper. Refilter if extracts are not clear.Analyze for P by colorimetry or inductively coupled plasma emission spectroscopy using a blank and standards prepared in the Olsen P extracting solution.
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Slide83Soil Test Phosphorus: Olsen PJ. Thomas Sims, University of Delaware
Perhitungan:P terekstraks Olsen (mg P/kg tanah) =[Konsentrasi P dalam ekstraks Olsen, mg/L ] x [ 0.020 L ekstrak ÷ 0.001 kg tanah]
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References:
Fixen
, P.E. and J.H. Grove. 1990. Testing soils for phosphorus. p. 141-180. In R.L.
Westerman
(ed.) Soil Testing and Plant Analysis. SSSA, Madison, WI.
Kuo
, S. 1996. Phosphorus. p. 869-919. In D.L. Sparks. (ed.). Methods of Soil Analysis: Part 3- Chemical Methods. SSSA, Madison, WI.
Olsen, S.R., C.V. Cole, F.S. Watanabe, and L.A. Dean. 1954. Estimation of available phosphorus in soils by extraction with sodium bicarbonate. USDA Circular 939. U.S. Government Printing Office, Washington D.C.
Schoenau
, J.J. and R.E.
Karamanos
. 1993. Sodium bicarbonate extractable P, K, and N. p. 51-58. In M. R. Carter (ed.) Soil Sampling and Methods of Analysis. Can. Soc. Soil Sci., Ottawa, Ontario.
Slide84Soil Test Phosphorus: Mehlich 1J. Thomas Sims, University of Delaware
The Mehlich 1 soil test for phosphorus (P), also known as the dilute double acid or North Carolina extractant, was developed in the early 1950s by Mehlich and his coworkers (Mehlich, 1953; Nelson et al. 1953). In the United States the Mehlich 1 procedure is primarily used in the southeastern and mid-Atlantic states as a multi-element extractant for P, K, Ca, Mg, Cu, Fe, Mn, and Zn. The Mehlich 1 extracts P from aluminum, iron, and calcium phosphates and is best suited to acid soils (pH < 6.5) with low cation exchange capacities (< 10 cmol/kg) and organic matter contents (< 5%). Kuo (1996) reported that the Mehlich 1 soil test was unreliable for calcareous or alkaline soils because it extracts large amounts of nonlabile P in soils with pH > 6.5, soils that have been recently amended with rock phosphate, and soils with high cation exchange capacity (CEC) or high base saturation. Dalam tanah-tanah seperti ini, kemasmaan larutan Mehlich-1 dinetralisir, sehingga mengurangi kemampuannya mengekstraks P . Penurunan efisiensi ekstraksi P juga dapat disebabkan oleh liat dan oksida hidrous aluminum dan besi (Nelson et al., 1953; Lins & Cox, 1989).
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Slide85Soil Test Phosphorus: Mehlich 1J. Thomas Sims, University of Delaware
Nilai P Mehlich-1 sebesar 20 - 25 mg P/kg tanah untuk uji Mehlich-1 umumnya dianggap optimum bagi pertumbuhan tanaman, meskipun nilai ini beragam di antara tipe-tipe tanah dan sistem pertanaman. For instance, Kamprath and Watson (1980) stated a Mehlich-1 P of 20 to 25 mg P/kg soil is adequate for plants grown in sandy soils but only 10 mg P/kg soil is required for fine-textured soils, a point supported by the work of Lins and Cox (1989).
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Slide86Soil Test Phosphorus: Mehlich 1J. Thomas Sims, University of Delaware
Peralatan Lab:No. 10 (2 mm opening) sieveAutomatic extractant dispenser, 25 mL capacity (If preferred, pipettes are acceptable.)Standard 5 cm3 and 1 cm3 stainless steel soil scoopsExtraction vessels, such as 50 mL Erlenmeyer flasks, and filter funnels (9 and 11 cm) and racksReciprocating or rotary shaker, capable of at least 180 epm (excursions per minute)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.)
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Slide87Soil Test Phosphorus: Mehlich 1J. Thomas Sims, University of Delaware
Pereaksi - Reagents:Mehlich 1 Extracting Solution (0.0125 M H2SO4 + 0.05 M HCl). Also referred to as dilute double acid or the North Carolina Extractant. Using a graduated cylinder, add 167 mL of concentrated HCl (12M) and 28 mL of concentrated H2SO4 (18M) to ~35 L of deionized water in a large polypropylene carboy. Buatlah volume akhir 40 L dengan menambahkan air bebas ion. Aduklah dnegan memasukkan gelembung udara ke dalam larutan 3 jam.
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Slide88Soil Test Phosphorus: Mehlich 1J. Thomas Sims, University of Delaware
Prosedur: Timbang 5.0 g (atau ambil 4 cm3) sampel tanah ayakan (< 2 mm), kering udara dan masukkan ke dalam labu ekstraksi 50 mL.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.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.Filter through a medium-porosity filter paper (Whatman No. 2 or equivalent).Analyze for P by colorimetry or inductively coupled plasma emission spectroscopy using a blank and standards prepared in the Mehlich 1 extracting solution.PERHITUNGAN:P terekstraks Mehlich -1 (mg P/kg tanah) =[Konsentrasi P dalam ekstraks Mehlich -1, mg/L ] x [ 0.020 L ekstrak ÷ 0.005 kgtanah]
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Slide89Soil Test Phosphorus: Mehlich 1J. Thomas Sims, University of Delaware
References:Kamprath, E.J. and M.E. Watson. 1980. Conventional soil and tissue tests for assessing the phosphorus status of soils. p. 433-469. In F. E. Khasawneh et al. (ed.) The role of phosphorus in agriculture. ASA, CSSA, and SSSA, Madison, WI.Kuo, S. 1996. Phosphorus. p. 869-919. In D. L. Sparks. (ed.) Methods of Soil Analysis: Part 3- Chemical Methods. SSSA, Madison, WI.Lins, I.D.G. and F.R. Cox. 1989. Effects of extractant and selected soil properties on predicting the optimum phosphorus fertilizer rate for growing soybeans under field conditions. Commun. Soil Sci. Plant Anal. 20:310-333.Mehlich, A. 1953. Determination of P, Ca, Mg, K, Na, and NH4. North Carolina Soil Test Division (Mimeo). Raleigh, NC.Nelson, W. L., A. Mehlich, and E. Winters. 1953. The development, evaluation, and use of soil tests for phosphorus availability. Agronomy 4:153-158.
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Slide90Soil Test Phosphorus: A Phosphorus Sorption IndexJ. Thomas Sims, University of Delaware
Kapasitas sorpsi P suatu tanah dapat ditentukan dengan eksperimen “batch equilibrium” yg dipakai untuk menghasilkan isotherm sorpsi. These isotherms are plots of the amount of P adsorbed from several solutions of known initial concentration vs. the P concentration at equilibrium for each solution. For example, Nair et al., (1984) proposed, based on an interlaboratory comparison study, a standard approach to construct P sorption isotherms, using a soil:solution ratio of 1:25 (w:v), six initial P concentrations (as KH2PO4 in a 0.01M CaCl2 matrix), and a 24 h equilibration period Hasil-hasil dari sorpsi isothermik ini dapat dipakai untuk menghitung maksimum P-sorpsi dan energi pengikat P untuk tanah-tanah dengan beragam sifat dan/atau dipengaruhi oleh teknologi bubidaya, seperti rotasi tanaman, olah tanah dan aplikasi rabuk organik.
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Slide91Soil Test Phosphorus: A Phosphorus Sorption IndexJ. 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.
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Slide92Soil Test Phosphorus: A Phosphorus Sorption IndexJ. Thomas Sims, University of Delaware
Peralatan Lab:Centrifuge dan tabung centrifuge poli-etilen 50 mL.Pengocok (end-over-end shaker preferred to ensure thorough mixing of soil and sorption solution).Peralatan filtrasi Millipore (0.45-μm pore size filters) dan labu-labu vakum.50 mL screw-top test tubes.Reagen:Phosphorus Sorption Solution (75 mg P/L): Dissolve 0.3295 g of monobasic potassium phosphate (KH2PO4) in 1 L of deionized H2O. Store in refrigerator until use.
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Slide93Soil Test Phosphorus: A Phosphorus Sorption IndexJ. Thomas Sims, University of Delaware
Prosedur:Timbanglah 1.00 g sampel tanah kering udara, lolos ayakan (2 mm) ke dalam tabung sentrifuge 50 mL.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.Place the tubes in the end-over-end shaker and shake for 18 h at 25±2oC.Centrifuge the samples at 2000 rpm for 30 minutes.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.Measure P concentration in the centrifugate colorimetrically or by inductively coupled plasma emission spectroscopy (ICP-AES).
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Slide94Soil Test Phosphorus: A Phosphorus Sorption IndexJ. 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 Cdimana: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).
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Slide95Soil Test Phosphorus: A Phosphorus Sorption IndexJ. Thomas Sims, University of Delaware
References:Bache, B.W., and E.G. Williams. 1971. A phosphate sorption index for soils. J. Soil Sci. 22:289-301.Mozaffari, P.M., and J.T. Sims. 1994. Phosphorus availability and sorption in an Atlantic Coastal Plain watershed dominated by intensive, animal-based agriculture. Soil Sci. 157:97-107.Nair, P.S., T.J. Logan, A.N. Sharpley, L.E. Sommers, M.A. Tabatabai, and T.L. Yuan. 1984. Interlaboratory comparison of a standardized phosphorus adsorption procedure. J. Environ. Qual. 13:591-595.Sharpley, A.N., S.J. Smith, B.A. Stewart, and A.C. Mathers. 1984. Forms of phosphorus in soils receiving cattle feedlot waste. J. Environ. Qual. 13:211-215.Simard, R.R., D. Cluis, G. Gangbazo, and A. Pesant. 1994. Phosphorus sorption and desorption indices for soils. Commun. Soil Sci. Plant Anal. 25:1483-1494.
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Slide96Determination of Water- and/or Dilute Salt-Extractable PhosphorusM.L. Self-Davis, University of ArkansasP.A. Moore, Jr., USDA-ARS, Fayetteville, ARB.C. Joern, Purdue University
Many methods exist to determine the various forms of soil phosphorus (P). Early interests in examining soil P were primarily based on determining the quantity of supplemental P needed to adequately meet the needs of crops. The method for using distilled water as an extractant to determine P needs of plants was examined in a paper by Luscombe et al. (1979). They found a good correlation between the concentration of water-extractable P and dry matter yield responses in ryegrass.One criticism of various other extractants is that they are either more acid or alkaline than the soil solution. Therefore, a portion of P extracted is actually of low availability.For example, extractants such as Mehlich 3, which contain strong acids, would be expected to dissolve calcium phosphates. Also, due to the specific chemical nature of many extractants, their use is limited to specific soil types. Using distilled water or 0.01 MCaCl2 overcomes these criticisms (Pote et al., 1995).
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Slide97Determination of Water- and/or Dilute Salt-Extractable PhosphorusM.L. Self-Davis, University of ArkansasP.A. Moore, Jr., USDA-ARS, Fayetteville, ARB.C. Joern, Purdue University
Peralatan :Shaker (reciprocating or end-over-end).Centrifuge.Centrifuge tubes (40 mL).Filtration apparatus (0.45 μm pore diameter membrane filter, or Whatman No. 42).Spectrophotometer with infrared phototube for use at 880 nm.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:Asam pekat hydrochloric acid (HCl).Reagents used for ascorbic acid technique for P determination, Murphy and Riley (1962).Larutan M calcium chloride (CaCl2).Chloroform.
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Slide98Determination of Water- and/or Dilute Salt-Extractable PhosphorusM.L. Self-Davis, University of ArkansasP.A. Moore, Jr., USDA-ARS, Fayetteville, ARB.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 thenegative effects of acidification minimal.
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Slide99Determination of Water- and/or Dilute Salt-Extractable PhosphorusM.L. Self-Davis, University of ArkansasP.A. Moore, Jr., USDA-ARS, Fayetteville, ARB.C. Joern, Purdue University
Prosedur Ekstraksi -- 0.01M CaCl2:Weigh out 1 g of dry soil into a 40 mL centrifuge tube. Add 25 mL of 0.01 M CaCl2 (you can add 2 drops of chloroform to inhibit microbial growth if desired) and shake for one hour on a reciprocating shaker. Centrifuge at 4000 rpm for 10 minutes. Larutan disaring dnegan kertas saring Whatman No. 42.
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Slide100Determination of Water- and/or Dilute Salt-Extractable PhosphorusM.L. Self-Davis, University of ArkansasP.A. Moore, Jr., USDA-ARS, Fayetteville, ARB.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]
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Slide101Determination of Water- and/or Dilute Salt-Extractable PhosphorusM.L. Self-Davis, University of ArkansasP.A. Moore, Jr., USDA-ARS, Fayetteville, ARB.C. Joern, Purdue University
References:Lee, G.R., N.L. Clesceri, and G.P. Fitzgerald. 1965. Studies on the analysis of phosphates in algal cultures. Internat. J. Air Water Poll. 9:715-722.Luscombe, P.C., J.K. Syers, and P.E.H. Gregg. 1979. Water extraction as a soil testing procedure for phosphate. Commun. Soil Sci. Plant Anal. 10:1361-1369. Murphy, J., and J.P. Riley. 1962. A modified single solution method for the determination of phosphate in natural waters. Anal. Chem. Acta 27:31-36.Olsen, S.R., and L.E. Sommers. 1982. Phosphorus. P. 403-430 In A.L. Page et al. (ed.) Methods of soil analysis. Part 2. 2nd ed. Agronomy Monogr. 9. ASA and SSSA, Madison, WI.Olsen, S.R., and F.S. Watanabe. 1970. Diffusive supply of phosphorus in relation to soil textural variations. Soil Sci. 110:318-327.Pote, D.H., T.C. Daniel, P.A. Moore, Jr., A.N. Sharpley, D.R. Edwards, and D.J. Nichols. 1995. Phosphorus: relating soil tests to runoff concentrations across five soil series. Agronomy Abstracts, p. 294, Am. Soc. Agron., Madison, WI.Pote, D.H., T.C. Daniel, A.N. Sharpley, P.A. Moore, Jr., D.R. Edwards, and D.J. Nichols. 1996. Relating extractable soil phosphorus to phosphorus losses in runoff. Soil Sci. Soc. Am J. 60:855-59.Sharpley, A.N. 1995. Dependence of runoff phosphorus on extractable soil phosphorus. J. Environ. Qual. 24:920-926.Soltanpour, P.N., F. Adams, and A.C. Bennett. 1974. Soil phosphorus availability as measured by displaced soil solutions, calcium chloride extracts, dilute-acid extracts, and labile phosphorus. Soil Sci. Soc. Am. Proc. 38:225-228.
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Slide102Bioavailable Phosphorus in SoilAndrew Sharpley, USDA-ARS, University Park, PA
Biologically available P (BAP) didefinisikan sebagai “….. Jumlah P-anorganik , yg dapat digunakan oleh populasi algae yg defisien P selama periode 24 jam atau lebih “ (Sonzogni et al., 1982). Jumlah P dalam tanah, sedimen, dan air yang secara potensial tersedia bagi serapan algae (bioavailable P) dapat dikuantifikasikan dengan “algal assays”, yg memerlukan waktu inkubasi hingga 100 hari (Miller et al., 1978). Thus, more rapid chemical extractions, such as those using NaOH (Butkus, et al., 1988; Dorich et al., 1980), NH4F (Porcella et al., 1970), ion exchange resin (Huettl et al., 1979) and citrate-dithionitebicarbonate (Logan et al., 1979), have been used routinely to estimate bioavailable P.The weaker extractants (NH4F and NaOH) and short-term resin extractions may represent P that could be utilized by algae in the photic zone of lakes under aerobic conditions. In contrast, the more severe extractants (citrate-dithionite-bicarbonate) represent P that may become bioavailable under the reducing conditions found in the anoxic hypolimnion of stratified lakes.
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Slide103Bioavailable Phosphorus in SoilAndrew 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.
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Slide104Bioavailable Phosphorus in SoilAndrew 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.
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Slide105Bioavailable Phosphorus in SoilAndrew Sharpley, USDA-ARS, University Park, PA
Iron-oxide-Impregnated PaperAnother P sink that has received attention is Fe-oxide impregnated filter paper, whichhas successfully estimated plant available P in a wide range of soils and managementsystems (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 describedfurther here.
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Slide106Bioavailable Phosphorus in SoilAndrew Sharpley, USDA-ARS, University Park, PA
RESIN PENUKAR-ANIONThe 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).
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Slide107Bioavailable Phosphorus in SoilAndrew Sharpley, USDA-ARS, University Park, PA
Ion-exchange Resin-Impregnated MembranesA 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).
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Slide108Bioavailable Phosphorus in SoilAndrew 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.
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Slide109Bioavailable Phosphorus in SoilAndrew Sharpley, USDA-ARS, University Park, PA
PERALATAN:The following equipment is needed to conduct BAP extraction of soil and analysis for P:Membran Resin, penukar anion.End-over-end shaker - used to equilibrate sample and sinkLabu Volumetrik – biasanya volume 25 atau 50 mLPipets untuk sampel aliquot dan reagen warnaSpectrophotometer untuk menentukan konsentrasi P dalam reagen yg menjadi berwarna kalau ketemu sampel.
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Slide110Bioavailable Phosphorus in SoilAndrew Sharpley, USDA-ARS, University Park, PA
Reagents:Membran ResinHydrochloric acid to extract P from the membranes - 1.0 M HCl (166 mL concentrated HCl in 2 L)Murphy and Riley Molybdenum Blue Color Reagent
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Slide111Bioavailable Phosphorus in SoilAndrew Sharpley, USDA-ARS, University Park, PA
Resin Strip Procedure: 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.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.Remove the resin membrane square and wash thoroughly with distilled water until all soil particles are removed.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.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.Mengukur konsentrasi P dua macam larutan secara terpisah. Jumlah total desorpsi P dari membran resin berbentuk kuadrat adalah jumlah dari dua larutan itu.
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Slide112Bioavailable Phosphorus in SoilAndrew Sharpley, USDA-ARS, University Park, PA
Perhitungan:P-terekstraks Resin (mg P/kg) = [Konsentrasi P dalam 1 MHCl, mg/L] x [0.04 L ÷ 0.001 kg]Resin BAP dalam runoff (mg P/L) = [konsentrasi P dalam 1 M HC1, mg/L] x [0.04L ÷ volume runoff, L]References:Abrams, M.M., and W.M. Jarrell. 1992. Bioavailability index for phosphorus using nonexchange resin impregnated membranes. Soil Sci. Soc. Am. J. 56:1532-1537.Amer, F., D.R. Bouldin, C.A. Black, and F.R. Duke. 1955. Characterization of soil phosphorus by anion exchange resin and adsorption by P-32 equilibration. Plant Soil 6:391-408.Barrow, N.J., and T.C. Shaw. 1977. Factors affecting the amount of phosphate extracted from soil by anion exchange resin. Geoderma 18:309-323.Butkus, S.R., E.B. Welch, R.R. Horner, and D.E. Spyridakis. 1988. Lake response modeling using biologically available phosphorus. J. Water Pollut. Cont. Fed. 60:1663-1669.Chardon, W.J. 2000. Phosphorus extraction with iron oxide-impregnated filter paper (P; test). In G.M. Pierzynski (ed.), Sediments, Residuals, and Waters. Southern Cooperative Series Bulletin No. 396, p. 27-30.Dorich, R.A., D.W. Nelson, and L.E. Sommers. 1980. Algal availability of sediment phosphorus in drainage water of the Black Creek watershed. J. Environ. Qual. 9:557- 563.Edwards, T., B. Ferrier, and R. Harriman. 1993. Preliminary investigation on the use of ion-exchange resins for monitoring river water composition. Sci. of Total Environ. 135:27-36.
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Slide113Total Phosphorous in SoilM.R. Bender and C.W. Wood, Auburn University
There have been many methods developed to extract and analyze total phosphorus (P)in soil (Bray and Kurtz, 1945; Muir, 1952; Jackson, 1958; Syers et al., 1968; Sommersand Nelson, 1972; Dick and Tabatabai, 1977; Olsen and Sommers, 1982; Bowman,1988). Two of the more commonly used and most recognizable methods of P extractionare sodium carbonate (Na2CO3) fusion and acid digestion. Of these methods, Na2CO3fusion 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.
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Slide114Total Phosphorous in SoilM.R. Bender and C.W. Wood, Auburn University
In recent years, more rapid methods for determining total P in soils have beendeveloped (Sommers and Nelson, 1972; Dick and Tabatabai, 1977; Bowman, 1988).Methods developed by Sommers and Nelson (1972) and Bowman (1988) are variationsof standard HClO4 digestion methods. These methods were shown to give a similardegree 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.
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Slide115Total Phosphorous in SoilM.R. Bender and C.W. Wood, Auburn University
Fusion Method (Olsen and Sommers (1982)):ReagentsAnhydrous sodium carbonate (Na2CO3)Larutan 4.5 M H2SO4Larutan 1 M H2SO4Ammonium 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.Larutan 2 M H2SO4Ascorbic 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.Potassium antimony tartrate (KSbO.C4H4O6). Prepare by dissolving 0.667 g of KSbO.C4H4O6 in 250 mL of distilled water.Mixed reagent. Mix 1:1 ratio of ascorbic acid and antimony reagents prior to use. Siapkan larutan segar sebanyak yang diperlukan.
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Slide116Total Phosphorous in SoilM.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)
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Slide117Total Phosphorous in SoilM.R. Bender and C.W. Wood, Auburn University
KOMENTARThe method for color development was described by Harwood et al. (1969) and is avariation of the method proposed by Murphy and Riley (1962). By increasing amount of antimony added, Harwood et al. (1969) found that the range of the calibration curve could be extended. This modification of the Murphy and Riley (1962) method was found to increase the upper limit of the calibration curve from 50 mg P/50ml sample to 150 mg P/50ml sample.It should be noted that presence of arsenic in the form of AsO4 in soil samples gives the same blue color as phosphate. To eliminate this problem, AsO4 can be reduced to AsO3 using a NaHSO3 solution as described in the following digestion method (Olsen and Sommers, 1982).PERHITUNGANTotal P, mg/kg =[Konsentrasi P dalam pengenceran initial 250 mL, mg/L] x [0.25 L ÷ masa tanah, kg]
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Slide118Total Phosphorous in SoilM.R. Bender and C.W. Wood, Auburn University
Digestion Method (Olsen and Sommers (1982)):ReagentsLarutan 60% Perchloric acid (HClO4)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.Standard phosphate solution. Prepare by dissolving 0.4393 g of oven-dried potassium dihydrogen phosphate (KH2PO4) in distilled water. Dilute solution to 1 L with distilled water. Standard solution contains 100 mg P/L.Sodium hydrogen sulfite (NaHSO3). Prepare by dissolving 5.2 g of reagent grade NaHSO3 in 100 mL of 0.5 M H2SO4. Persiapkan reagen setiap mingguan.
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Slide119Total Phosphorous in SoilM.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.PERHITUNGANTotal P, mg/kg =[Konsentrasi P dalam pengenceran initial 250 mL , mg/L] x [0.25 ÷ masa tanah, kg]
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Slide120Total Phosphorous in SoilM.R. Bender and C.W. Wood, Auburn University
Metode Oksidasi Alkaline (Dick and Tabatabai (1977)):Pereaksi - ReagentsSodium 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.Larutan 90 % formic acidLarutan 2.5 M H2SO4Ammonium molybdate -Antimony potassium tartrate solution. Prepare by dissolving 12 g of ammonium molybdate in 250 mL of distilled water, and dissolving 0.2908 g of antimony potassium tartrate in 100 mL of distilled water. Add both solutions to 1 L of 2.5 M sulfuric acid, and dilute volume to 2 L with distilled water. Store reagent in a cool place, in a dark Pyrex glass bottle.Ascorbic acid. Prepare by dissolving 1.056 g of ascorbic acid in 200 mL of ammonium molybdate - antimony reagent. Prepare reagent daily.Standard phosphate solution. Prepare by dissolving 0.2195 g of potassium dihydrogen phosphate (KH2PO4) in distilled water. Dilute solution to 1L with distilled water. Standard solution contains 50 mg P/L.
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Slide121Total Phosphorous in SoilM.R. Bender and C.W. Wood, Auburn University
Prosedur kerjaPlace a 100 to 200 mg sample of finely ground, air-dried soil in a 50 mL boiling flask.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.To analyze for total P, transfer aliquots of 1 to 2 mL into 25 mL volumetric flasks.Add 4 mL of ascorbic acid reagent, and bring solution up to volume with distilled water.Stopper flask and mix solution. Allow solution to stand for 30 min for color development.Optical density of sample should be measured at a wavelength of 720 nm.
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Slide122Total Phosphorous in SoilM.R. Bender and C.W. Wood, Auburn University
KOMENTARThis 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 hypobromitetreatment will destroy any residual hypobromite remaining after oxidation of the sample.PERHITUNGANTotal P, mg/kg =[konsentrasi P dalam larutan initial asam fosmat /H2SO4, mg/L] x [0.03 L ÷ masa tanah, kg]
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Slide123Total Phosphorous in SoilM.R. Bender and C.W. Wood, Auburn University
References:Bowman, R.A. 1988. A rapid method to determine total phosphorus in soils. Soil Sci. Soc. Am. J. 52:1301-1304.Bray, R.H., and L.T. Kurtz. 1945. Determination of total, organic, and available forms of phosphorus is soils. Soil Sci. 59:39-45.Dick, W.A., and M.A. Tabatabai. 1977. An alkaline oxidation method for determination of total phosphorus in soils. Soil Sci. Soc. Am. J. 41:511-514.Harwood, J.E., R.A. van Steenderen, and A.L. Kuhn. 1969. A rapid method for orthophosphate analysis at high concentrations in water. Water Res. 3:417-423.Jackson, M.L. 1958. Soil chemical analysis. Prentice-Hall, Inc., Englewood Cliffs, N.J. Muir, J.W. 1952. The determination of total phosphorus in soil. Analyst 77:313-317.Murphy, J., and J.P. Riley. 1962. A modified single solution method for determination of phosphate in natural waters. Anal. Chim. Acta 27:31-36.Olsen, S.R., and L.E. Sommers. 1982. Phosphorus. pp. 403-430. In: A.L. Page. R.H. Miller, and D.R. Keeney (eds.), Methods of Soil Analysis. 2nd ed. Agronomy Series No.9, Part 2. Soil Science Society of America, Inc., Madison, WI.Sherrell, C.G., and W.M.H. Saunders. 1966. An evaluation of methods for the determination of total phosphorus in soils. N.Z.J. Agric. Res. 9:972-979.Sommers, L.E., and D.W. Nelson. 1972. Determination of total phosphorus in soils: a rapid perchloric acid digestion procedure. Soil Sci. Soc. Amer. Proc. 36:902-904.Syers, J.K., J.D.H. Williams, A.S. Campbel, and T.W. Walker. 1967. The significance of apatite inclusions in soil phosphorous studies. Soil Sci. Soc. Amer. Proc. 31:752-756.Syers, J.K., J.D.H. Williams, and T.W. Walker. 1968. The determination of total phosphorus in soils and parent materials. N.Z.J. Agric. Res. 11:757-762.
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