MK. Dasar Ilmu Tanah
bahan kajian:
FOSFAT
DALAM TANAH
diabstraksikan Oleh
soemarno.jursntnhfpub. Okt 2012
Problematik Fosfor
Jumlah
sedikit yang
terdapat
dalam tanah
Adanya fiksasi
fosfat yang
menyolok
Ketidaktersediaan
fosfat yg sdh
ada dalam
tanah
FOSFAT - TANAH
The Soil P Cycle
The soil P cycle. (Image from Sharpley and Sheffield, Livestock
and Poultry Environmental Stewardship Curriculum)
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:
…..
http://croptechnology.unl.edu/pages/informationmodule.php?idinformationmodule=1118084123&topicorder=5&maxto=7&minto=1
FOSFAT - TANAH
Phosphorus (P)
Phosphorus, another of the macronutrients 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 H2PO4at 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.
Soil phosphorus dynamics including potential
tranformations and fates of applied fertilizer P.
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:
….. http://www.extension.org/pages/9873/phosphorus-p
FOSFAT - TANAH
Process-based assessment of
plant-available soil P
1.
Achat David L, Bakker Mark R, Morel
Christian, 2009. Process-based
assessment of P availability in a low Psorbing forest soil using isotopic
dilution methods. Soil Sci Soc Am J
73:2131-2142;
Achat David L, Bakker Mark R,
Augusto Laurent, Saur Etienne,
Dousseron Lysiane, Morel Christian.
2009. Evaluation of the phosphorus
status of P-deficient podzols in
temperate pine stands combining
isotopic dilution and extraction
methods. Biogeochemistry, 92, 183:200.
2.
Morel C., H. Tiessen, J.O. Moir and
J.W.B. Stewart, 1994. Phosphorus
transformations and availability under
cropping and fertilization assessed by
isotopic exchange. Soil Science Society
of American Journal, 58 : 1439-1445
diunduh dari:
….. http://www.bordeauxaquitaine.inra.fr/tcem_eng/recherche/nutrition_minerale_et_gestion_de_la_fertilite
Senyawa P
dalam tanah
Senyawa P an-organik
1. Senyawa Kalsium
2. Senyawa besi dan aluminium
Senyawa
Fluor-apatit
Karbonato-apatit
Hidroksi-apatit
Oksi-apatit
Trikalsium-fosfat
Dikalsium-fosfat
Monokalsium-fosfat
Senyawa P-organik:
1. Fitin dan derivatifnya
2. Asam Nukleat
3. Fosfolipida
Rumus
3 Ca3(PO4)2.CaF
3 Ca3(PO4)2.CaCO3
3 Ca3(PO4)2.Ca(OH)2
3 Ca3(PO4)2.CaO
Ca3(PO4)2
CaHPO4
Ca(H2PO4)2
Kelarutan
naik
Kemasaman tanah (pH):
Ketersediaan P
anorganik dalam
tanah
Ketersediaan P bagi tanaman tgt pd bentuk anion fosfat,
selanjutnya bentuk anion ini tgt pada pH
+OH-
+ OH-
H2O + HPO4=
H2PO4Paling tersedia
bagi tanaman
H2O + PO4---
larutan tanah
sangat masam
larutan tanah
sangat alkalin
% kepekatan
100
50
H2PO4-
H3PO4
HPO4=
PO3-3
0
0
2
4
6
8
10
12
14
pH larutan
Ketersediaan
P-anorganik
tanah masam
Pengendapan oleh kation Fe, Al, Mn
Al3+ + H2PO4- + H2O
2H+ + Al(OH)2H2PO4
larut
tdk larut
Dlm tanah masam biasanya konsentrasi kation Fe, Al
lebih besar dp anion fosfat, sehingga reaksi berlangsung
ke arah kanan
Pengikatan oleh hidro-oksida: Fiksasi fosfat
OH
OH
Al OH + H2PO4OH- + Al OH
OH
larut
H2PO4 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
Dlm kristal silikat
2H+ + Al(OH)2H2PO4
tidak larut
Ketersediaan
P-anorganik
pd pH tinggi
Pengendapan oleh kation Ca++ atau CaCO3
H2PO4- + 2 Ca++
Ca3(PO4)2 + 4H+
larut
tidak larut
H2PO4- + 2 CaCO3
larut
Ca3(PO4)2 yang terbentuk dalam reaksi di
atas, masih dapat berubah menjadi
bentuk-bentuk yang lebih sukar larut,
seperti senyawa hidroksi-, oksi- ,
karbonat-, atau fluor-apatit.
Reaksi-reaksi ini semua terjadi pada
tanah-tanah masam yang dikapur dengan
dosis tinggi (Pengapuran berat)
Ca3(PO4)2 + 2CO2 + 2H2O
tidak larut
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
Fosfat segera / mudah tersedia
Larut air : NH4-fosfat, Ca(H2PO4)2
Tidak larut: CaHPO4 dan Ca3(PO4)2
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.
Kemampuan tanah menjerap
(Daya Jerap) P
Tanah
Latosol Purwokerto
Mineral Liat
Haloisit
Perlakuan
pH Daya Jerap P (*)
Tanpa kapur
Dengan kapur
5.7
5.9
30.110
26.600
LatosolCibodas
Kaolinit
Tanpa kapur
Dengan kapur
5.2
5.6
45.520
40.920
PodsolikGajrug
Smektit
Tanpa kapur
Dengan kapur
4.8
5.3
36.950
33.180
PodsolikSamarinda
Smektit
Kaolinit
Tanpa kapur
Dengan kapur
4.6
5.2
29.280
16.370
GrumusolYogjakarta
Smektit, Kaolinit
Haloisit
Tanpa kapur
6.7
14.960
Andosol 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)
Pengelolaan P - Tanah
Limbah tanaman
Pupuk kandang
BOT
Tanaman
Pupuk buatan
Mineral tanah
P-tanah Tersedia
Pencucian
Erosi
Pengendalian P-tersedia dalam tanah:
1. Pengapuran
3. Pengendalian fiksasi P-tanah
2. Penempatan pupuk
Fiksasi
Siklus Lambat
P-anorganik
P-mineral
primer
(HCl-Pi)
P-mineral
sekunder
(NaOH-Pi)
(P-residu)
P-terfiksasi
(Sonic-Pi)
(P-residu)
Siklus Cepat
P-anorganik & Organik
P- larutan
tanah
P-terlarut labil
(Resin-P)
Siklus Lambat
P-Organik
P- dalam
tanaman &
jasad tanah
P-terfiksasi labil
(Bikarbonat-Po)
P-organik
terfiksasi secara
kimia dan fisika
(Sonic-Po)
(Residu-Po)
P-terlarut agak
labil
(P-terfiksasi)
(Bikarbonat-Pi)
P-terfiksasi
agak labil
(NaOH-Po)
Siklus Transformasi P-tanah (Hedley et al. 1982)
FOSFAT - TANAH
Schematic representation of P cycle in soil
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:
….. http://www.gnb.ca/0173/30/0173300016-e.asp
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.
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 1000 - 3000 ppm P
7. Vertisol umumnya 20 - 90 ppm P
8. Entisol & Inceptisols: beragam p-totalnya
9. Oxisols umumnya < 200 ppm P
10. …..
1.
2.
3.
4.
5.
P-organik = 20-50 % total P-tanah
Oxisols, Ultisols, Alfisols: P-organik = 60-80% P-total
C:P rasio dalam tanah = 240:1 -- 110:1
N:P rasio dlm tanah = 20:1 -- 9:1
Mineralisasi P-organik sukar diukur, karena ion H2PO4yg dilepaskan ke tanah dengan cepat difiksasi menjadi
bentuk-bentuk P-anorganik
6. Pemupukan N dan P mempercepat mineralisasi Porganik
7. P-organik dlm tanah menjadi sumber P yg penting bagi
tanaman kalau tidak ada pemupukan P.
BAHAN
ORGANIK
SUMBER P
Komponen kualitas bahan organik sebagai sumberP:
1. Nisbah C/N (nilai kritisnya 25-30)
2. Nisbah C/P ( < 200: mineralisasi P
> 300 : imobilisasi P)
3. P-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
1.
2.
3.
4.
P - ANORGANIK: Fraksi aktif & Fraksi tidak aktif
Fraksi aktif : Ca-P, Al-P dan Fe-P
Fraksi tdak-aktif : Occluded-P dan Reductant-soluble P
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
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:
How much of the soil P is available for plant
uptake?
Phil Moody1, Grant Pu1 and Mike Bell2
1DERM, Dutton Park, 4102 Qld
2QAAFI, Kingaroy, 4610 Qld
Conceptual diagram of P pools extracted by the Colwell-P
method.
http://www.grdc.com.au/Research-and-Development/GRDC-Update-Papers/2012/04/How-much-of-the-soil-P-isavailable-for-plant-uptake …..
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 Pdepleted soils was then determined
in a P addition experiment using
the soils from the P depletion trial.
diunduh dari:
Conceptual diagram of P pools extracted by the BSES-P
method
http://www.grdc.com.au/Research-and-Development/GRDC-Update-Papers/2012/04/How-much-of-the-soil-P-isavailable-for-plant-uptake …..
FOSFAT - TANAH
. Soil tests for assessment of available P
Crop P uptake
Plot of cumulative crop P uptake against ColwellP for 15 soils used in the glasshouse depletion
experiment.
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 91440 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:
http://www.grdc.com.au/Research-and-Development/GRDC-Update-Papers/2012/04/How-much-of-the-soil-P-isavailable-for-plant-uptake …..
Faktor
Retensi P
dalam tanah
TIPE LIAT
Tanah-tanah liat lebih banyak meretensi & memfiksasi ppupuk 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 reorientasikristal yg melibatkan hasil fiksasi P
Implikasi penting adalah waktu pemupukan P dan penempatan pupuk P
dalam tanah.
Bgm pd tanah yg mempunyai kapasitas fiksasi P tinggi ? …………..
Bgm pd tanah yg mempunyai kapasitas fiksasi P rendah? …………
Faktor
Retensi P
dalam tanah
pH TANAH
Kisaran pH tanah yg optimum bagi ketersediaan p-tanah adalah
5.5 - 7.0
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
…………………………..
Faktor
Retensi P
dalam tanah
BAHAN ORGANIK Lanjutan …….
Dekomposisi bahan organik menghasilkan anion-anion yang mampu
membentuk senyawa kompleks dengan Fe dan Al, sehingga kationkation 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 bertahuntahun kemungkinan akan:
1. Mereduksi dosis pupuk P saat ini
2. Menggunakan lebih banyak fosfat yg ada dalam tanah
3. Kombinasi keduanya
…………………..
Fiksasi P-pupuk , %
100
80
60
40
20
Pasio R2O3 : P2O5
1. Proses yg mengubah ketersediaan P-tanah yg diukur
dengan pertumbuhan tanaman
2. Transformasi monokalsium fosfat (superfosfat) yg
soluble menjadi Ca-P, Fe-P dan Al-P yg kurang soluble
3. Pada tanah alkalis: Ca-P dan Mg-P yg insoluble
4. Pd tnh masam: Fe-P dan Al-P yg insoluble
5. Al+++ + mono-kalsium fosfat ------ Al(OH)2H2PO4
(liming with phosphorus)
6. Kapasitas fiksasi P = F(oksida Fe dan Al; Aldd)
7. Intensitas Fiksasi P:
Oksida > Oksida > Liat 1:1 > Liat 2:1
amorf
kristalin
Tanah
Liat dominan % Liat
Fixed P (ppm)
Adsorpsi Max.
Inceptisol Montmorilonit
Ultisol
Kaolinit
Oxisol
Kaolinit
Andept
Alofan
Sumber: NCSU, 1973
27
38
36
11
106
480
531
1050
Pd 0.2 ppm P lrt tnh
83
360
395
670
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. 96-106
Soil P saturation indices and P Langmuir adsorption maximum (Smax) 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 Smax and develop P saturation indices for 28
Oklahoma benchmark soils and to use path analysis and multiple regression to examine the
relationships between Smax and soil properties.
Soil samples were analyzed for pH, clay content, oxalate extractable P (Pox), Al (Alox), Fe (Feox), and
Mehlich-3 (M3) extractable P (PM3), Al (AlM3), Fe (FeM3), Ca (CaM3), and Mg (MgM3). The Smax value
and saturation indices based on oxalate and M3 extractions were determined.
The Smax value ranged from 34 to 500 mg kg−1 and was highly correlated with clay content (r = 0.79),
organic C (r = 0.80), Alox (r = 0.88), and Feox (r = 0.83). Soil pH was not correlated (p > 0.05) with
Smax Path analysis showed significant direct effects (p < 0.01) between Alox and Smax and between Feox
and Smax but these relationships were highly influenced by indirect effects of Alox and Feox
Multiple regression agreed well with path analysis and found that the combination of Alox and Feox
were the two most important soil properties related to Smax of the soils studied. Significant
relationships existed between AlM3 (r = 0.54) and Smax and between FeM3 (r = 0.54) and Smax Three P
saturation indices studied were highly correlated (p < 0.05) with each other.
Our results show that Smax of Oklahoma soils may be predicted with oxalate extractable Al and Fe or
M3 extractable Al, Fe, and Ca.
diunduh dari:
https://www.soils.org/publications/sssaj/abstracts/69/1/0096?access=0&view=article …..
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. 96-106
diunduh dari:
https://www.soils.org/publications/sssaj/abstracts/69/1/0096?access=0&view=article …..
1. H2PO4- dlm larutan tanah < 10 ppm, dlm tanaman 2000 ppm
2. Konsentrasi optimum unt jagung dan buncis:
0.07 ppm pd tnh berliat Ultisol , 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 0.07 - 0.2 ppm P dlm
larutan tanah
REAKSI P
tanah
ALKALINE
PRESIPITASI DIKALSIUM FOSFAT
Pada kondisi Ph tanah yang tinggi dan kaya kalsium, terjadi
pengendapan senyawa-senyawa:
1. Kalsium fosfat: Ca3(PO4)2; 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 garamgaram tidak larut dari kalsium, fosfat, dan mungkin CO3= atau OHReaksi retensi fosfat oleh liat-liat yang jenuh kalsium: Liat-Ca-H2PO4
Tiga faktor penting:
1. Aktivitas Ca++
2. Jumlah dan ukuran partikel CaCO3 bebas
3. Jumlah liat yang ada dlm tanah
…………………..
P-aded (ppm)
1200
Oxisol, 45% liat
Sumber: Fox, 1974
1000
Andept
800
600
Ultisol , 38% liat
400
200
Tnh Montmorilonit, 40% liat
0.001
0.01
0.05 0.1 0.2
P dlm larutan tanah, ppm
1.0
Tanaman
Hasil, t/ha
P-removal, kg/ha
1. Jagung
Biji
Jerami
Biji
Jerami
: 1.0
: 1.5
: 7.0
: 7.0
6
3
20
14
2. Padi
Biji
Jerami
Biji
Jerami
: 1.5
: 1.5
: 8.0
: 8.0
7
1
32
5
3. Nanas
Buah
: 12.5
4. Tebu 2 th
Above ground: 100
300
Sumber: Sanchez, 1976.
2.3
20
35
Hasil relatif (%)
100
80
Ubijalar: toleran
tanah miskin P
60
40
20
Jagung: intermediate
Lettuce: In-tolerant
0.003 0.006
0.050 0.100 0.200 0.400
P- larutan tanah, ppm
1.600
Tanaman
1.
2.
3.
4.
5.
6.
7.
8.
P-larutan tnh yg menghasilkan 95% hasil maks., ppm
Lettuce
Tomat
Cucumber
Kedelai (vegetable)
Ubijalar
Jagung
Sorghum
Kubis
Sumber: Fox et al. (1974)
0.40
0.25
0.20
0.20
0.10
0.60
0.50
0.04
Tanaman
1.
2.
3.
4.
5.
6.
7.
8.
Internal P Requirement, %P
Stylosanthes humilis
Centrosema pubescens
Desmodium intortum
Digitaria decumbens
Panicum maximum
Pennisetum clandestinum
Paspalum dilatatum
Sumber: Andrew & Robins (1969, 1971)
0.17
0.16
0.22
0.16
0.19
0.22
0.25
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: 100 - 150 kg P2O5/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 40-50 % 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 5.5 - 6.0 umumnya meningkatkan ketersediaan
P dalam tanah, mengurangi fiksasi P
Hasil biomasa , %
100
Dikapur hingga pH = 5.5
80
Tdk dipakur pH= 4.8
60
40
Tingkat kritis
20
0
115
230
Pemupukan P (ppm P)
Sumber: Mendez-Lay (1974), Tnh Oxisol.
460
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.
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 garamgaram tidak larut dari kalsium, fosfat, dan mungkin CO3= atau OHReaksi retensi fosfat oleh liat-liat yang jenuh kalsium: Liat-Ca-H2PO4
Tiga faktor penting:
1. Aktivitas Ca++
2. Jumlah dan ukuran partikel CaCO3 bebas
3. Jumlah liat yang ada dlm tanah
…………………..
Granula Monokalsium fosfat:
MONO
KALSIUM
FOSFAT
H2O
H2O
H2O
Consentrated medium, pH 1.5, dimana CaH2PO4 dan CaHPO4
bergerak ke luar
Melarutkan Fe, Al, dan Mn
Pembentukan besi-fosfat, Al-fosfat, Mn-fosfat yg mengendap
MnPO4
FePO4
AlPO4
NILAI
KOMPARATIF
PUPUK
FOSFAT
1. Bentuk fosfat yang tersedia bagi tanaman ada dua, yaitu Fosfat-LarutAir dan Fosfat-Larut-Sitrat.
Namun demikian respon tanaman
terhadap kedua bentuk fosfat ini sangat beragam.
2. Untuk mendapatkan hasil maksimum bagi tanaman semusim yg sistem
perakarannya terbatas, umumnya diperlukan pupuk P yang banyak
mengandung fosfat-larut-air.
3. Untuk tanaman perennial yang sistem perakarannya luas (ekstensif),
tingginya tingkat kelarutan fosfat dalam air (>60%) tidak menjadi
faktor penting.
4. Untuk tanaman jagung, terutama pada saat awal pertumbuhannya,
memerlukan fosfat yang larut air.
5. Kalau jumlah pupuk fosfat terbatas, respon tanaman paling baik akan
diperoleh kalau pupuk fosfat tsb mudah larut air dan penempatan
pupuk di dekat benih atau bibit. Hal seperti ini sangat penting bagi
tanah-tanah yang miskin fosfat.
6. Pada tanah masam hingga netral, pupuk P granuler yg mudah larut air, biasanya lebih efektif
daripada pupuk P yang berupa bubukan, kalau pupuk dicampur dg tanah. Pada batas-batas
kondisi tertentu, semakin besar ukuran granula pupuk, efektifitasnya semakin baik.
7. Pada tanah netral hingga masam, “band application” bubukan pupuk P yg mudah larut air
akan memberikan hasil yg lebih baik dibandingkan dg pemakaian pupuk yg dicampur
dengan tanah.
NILAI
KOMPARATIF
PUPUK
FOSFAT
8. Pada tanah-tanah berkapur, pupuk fosfat larut air yg
berbentuk granula seringkali memberikan hasil lebih baik.
Pupuk fosfat-nitrat granuler yg kelarutan airnya rendah
(<50%) tidak cocok untuk tanah-tanah berkapur.
9. Hasil terbaik dapat diperoleh dengan bahan-bahan yg
kelarutan airnya rendah, kalau diberikan dalam bentuk
bubukan dan dicampur dengan tanah berkapur
10. Monoammonium fosfat (MAP) umumnya lebih cocok untuk tanahtanah 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.
HASIL-HASIL
PENELITIAN
FOSFAT-TANAH
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:
…. http://www.grasslands.org.au/resources/Articles/NewsletterArticle1.html.
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
Soil P cycle - pools and pathways.
Modified from [McLaughlin et al. 1999]
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.
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).
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:
…. http://www.grasslands.org.au/resources/Articles/NewsletterArticle1.html.
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.
2.
3.
4.
5.
6.
Increased physical exploration of the soil;
Increased P movement into mycorrhizal hyphae;
Modification of the root environment;
Efficient transfer of P to plant roots;
Increased storage of absorbed P; and
Efficient utilisation of P within the plant.
diunduh dari:
…. http://www.grasslands.org.au/resources/Articles/NewsletterArticle1.html.
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:
…. http://www.grasslands.org.au/resources/Articles/NewsletterArticle1.html.
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]).
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:
…. http://www.grasslands.org.au/resources/Articles/NewsletterArticle1.html.
Formation of Apatite from Superphosphate in the Soil
G. NAGELSCHMIDT & H. L. NIXON
Nature 154, 428-429 (30 September 1944) | doi:10.1038/154428b0
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:
…. http://www.nature.com/nature/journal/v154/n3909/abs/154428b0.html
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. 291-296 . 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 Ca2+.
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 Caexchange 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 Ca2+ and H2PO-4 in the soil solution.
diunduh dari:
….. https://www.soils.org/publications/sssaj/abstracts/50/2/SS0500020291
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 243–248
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.
diunduh dari:
….. http://www.sciencedirect.com/science/article/pii/S0305440396900217
. Phosphorus movement through soils
and groundwater: Application of a timedependent sorption model
Goen E. Ho , Suprihanto Notodarmojo
Water Science and Technology. Volume 31, Issue 9, 1995, Pages 83–90
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.
diunduh dari:
….. http://www.sciencedirect.com/science/article/pii/027312239500409G
. 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 279-295
A. Violante, M. Pigna, M. Ricciardella, L. Gianfreda
.
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.
diunduh dari: ….. http://www.sciencedirect.com/science?_ob=ArticleListURL&_method=list&_ArticleListID=113365860&_sort=r&_st=13&view=c&_acct=C000228598&_version=1&_urlVersion=0&_userid=10&md5=224dcd904b9d004a1df68f25a4f15b9f
&searchtype=a
Managing Phosphorus for Crop Production
Penn state Extension - Crop Management Extension Group-
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.
diunduh dari: …. http://extension.psu.edu/cmeg/facts/agronomy-facts-13.
Managing Phosphorus for Crop Production
Penn state Extension - Crop Management Extension Group-
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.
diunduh dari:
…. http://extension.psu.edu/cmeg/facts/agronomy-facts-13.
Managing Phosphorus for Crop Production
Penn state Extension - Crop Management Extension Group-
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 earlyseason soil conditions. This is why some crops respond to phosphorus applied at planting
in starter fertilizers even in relatively high phosphorus soils.
diunduh dari:
…. http://extension.psu.edu/cmeg/facts/agronomy-facts-13.
Managing Phosphorus for Crop Production
Penn state Extension - Crop Management Extension Group-
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.
diunduh dari:
…. http://extension.psu.edu/cmeg/facts/agronomy-facts-13.
Macroscale Chemical Properties and X-Ray Absorption Spectroscopy of Soil
Phosphorus
Dean Hesterberg. Developments in Soil Science. Volume 34, 2010, Pages 313–356
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.
diunduh dari:
….. http://www.sciencedirect.com/science/article/pii/S0166248110340116
Macroscale Chemical Properties and X-Ray Absorption Spectroscopy of Soil
Phosphorus
Dean Hesterberg. Developments in Soil Science. Volume 34, 2010, Pages 313–356
. 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 (Pt) 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). (HnPO4n−3, n = 1
or 2, typically).
diunduh dari:
….. http://www.sciencedirect.com/science/article/pii/S0166248110340116
Macroscale Chemical Properties and X-Ray Absorption Spectroscopy of Soil
Phosphorus
Dean Hesterberg. Developments in Soil Science. Volume 34, 2010, Pages 313–356
Comparison of a lability
model (based on Olsen
and Khasawneh, 1980)
and a chemical
speciation model for soil
phosphorus.
The speciation model
includes multiple,
hypothesized species
along a continuum of
lability, with lability
varying with soil
chemical conditions as
illustrated for pH.
diunduh dari:
….. http://www.sciencedirect.com/science/article/pii/S0166248110340116
Macroscale Chemical Properties and X-Ray Absorption Spectroscopy of Soil
Phosphorus
Dean Hesterberg. Developments in Soil Science. Volume 34, 2010, Pages 313–356
Solubility of selected Ca-, Al-, and
Fe-phosphate minerals predicted by
thermodynamics for equilibrium
conditions in soils when Ca2+
activity is 10−2.5 or is fixed by calcite
with partial pressure of CO2(g) =
0.0003 atm
(revised from Lindsay, 1979, with
permisson from the author).
diunduh dari:
….. http://www.sciencedirect.com/science/article/pii/S0166248110340116
Macroscale Chemical Properties and X-Ray Absorption Spectroscopy of Soil
Phosphorus
Dean Hesterberg. Developments in Soil Science. Volume 34, 2010, Pages 313–356
Sorption isotherms for phosphate on
noncrystallines (non-xls) Alhydroxide, 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 singlemineral systems, and represents how
the mineral mixture would sorb
phosphate if the system behaved as a
linear combination of the individual
minerals (qi = sorbed P and ci =
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).
diunduh dari:
….. http://www.sciencedirect.com/science/article/pii/S0166248110340116
Macroscale Chemical Properties and X-Ray Absorption Spectroscopy of Soil
Phosphorus
Dean Hesterberg. Developments in Soil Science. Volume 34, 2010, Pages 313–356
Phosphate sorption capacities of
selected phyllosilicates and oxide
minerals as a function of surface area
determined by the BET (BrunauerEmmett-Teller) method (data from
Violante and Pigna, 2002). The
quadratic regression model is fit to
the data at pH 5.
diunduh dari:
….. http://www.sciencedirect.com/science/article/pii/S0166248110340116
Macroscale Chemical Properties and X-Ray Absorption Spectroscopy of Soil
Phosphorus
Dean Hesterberg. Developments in Soil Science. Volume 34, 2010, Pages 313–356
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
diunduh dari:
….. http://www.sciencedirect.com/science/article/pii/S0166248110340116
Macroscale Chemical Properties and X-Ray Absorption Spectroscopy of Soil
Phosphorus
Dean Hesterberg. Developments in Soil Science. Volume 34, 2010, Pages 313–356
Normalized
phosphorus K-edge
XANES spectrum and
derivative XANES
spectrum for variscite
(AlPO4·2H2O),
showing spectral
features attributable to
bound states and
continuum states.
diunduh dari:
….. http://www.sciencedirect.com/science/article/pii/S0166248110340116
. Phosphorus cycle in agricultural soils.
diunduh dari:
…..
http://www.biocyclopedia.com/index/plant_nutrition/essential_elements_macronutrients/phosphorus/nature_and_transformations_of
_soil_phosphorus.php
IKTISAR
FOSFAT TANAH
1. P dalam tanah berbentuk organik dan an-organik.
Konsentrasi P-anorganik (H2PO4- dan HPO4=) dalam
larutan tanah merupakan faktor sangat penting yg
menentukan ketersediannya bagi tanaman
2. Konsentrasi ion fosfat dlm larutan tanah ditentukan oleh
kecepatan reaksi imobilisasi biologis dan reaksinya dg fraksi
mineral tanah. Tanah berliat (terutama liat tipe 1:1 dan
oksida hidrous Fe an Al) memfiksasi ortofosfat menjadi
bentuk yg tidak tersedia bagi tanaman.
3. Tanah berkapur umumnya mempunyai ketersediaan P rendah. Ion
fosfat dijerap pada permukaan partikel halus kalsium karbonatdan
selanjutnya dikonversi menjadi bentuk apatit yg tidak larut, atau
mengalami proses pengendapan langsung dari larutan tanah menjadi
kalsium fosfat.
4. Ketersediaan pupuk fosfat larut air dapat ditingkatkan dengan jalan menempatkan bahan
pupuk secara “banding” dlm tanah (ditugal atau digarit). Hasil yag serupa dapat diperoleh
dengan jalan granulasi bahan pupuk.
5. Terminologi khusus untuk pupuk fosfat adalah: Larut air, Larut sitrat, Tersedia, dan Total
Fosfat.
IKTISAR
FOSFAT TANAH
6. Pupuk fosfat dapat diklasifikasikan berdasarkan proses
pembuatannya, menjadi: Heat-processed phosphate, dan
Acid-treated Phosphate.
7. Reaksi pupuk fosfat larut air dengan berbagai komponen tanah
menghasilkan “produk reaksi pupuk - tanah”. Kelarutan hasil reaksi
inilah yang menentukan ketersediaan fosfat bagi tanaman
8. Kandungan air tanah sangat menentukan
efektifitas dan laju
ketersediaan pupuk fosfat. Pada kondisi air tanah kapasitas lapangan
sekitar 50-80 % fosfat larut air dapat bergerak ke luar dari granula
pupuk dalam periode 24 jam.
6.