Transcript DIT-BAHAN ORGANIK TANAH

MK. DASAR ILMU TANAH
BAHAN ORGANIK TANAH
Oleh:
Soemarno
JURUSAN TANAH FPUB NOP. 2013
SIKLUS KARBON
Tanaman
CO2
Hewan
Pupuk
Kandang
Reaksi
dalam
Tanah
Aktivitas Mikroba
CO2
Kehilangan drainage CO2, senyawa karbonat
dari K, Ca, Mg, dll.
Pemerangkapan Karbon
• Tanah menangkap karbon dan menyimpan
dalam bentuk BOT dan minerqal karbonat
• Sekitar 75% dari cadangan karbon di daratan
berupa BOT
• Penurunan cadangan BOT disebabkan:
– Mineralisasi BOT
– Erosi tanah
– Pencucian ke dalam tanah dan groundwater.
Penangkapan Karbon oleh Tanah dapat ditingkatkan dengan
cara:
• Mengubah praktek pertanian :
– No-till agriculture or organic agriculture
– Limited used of N fertilizer (C released during N
fertilizer manufacture)
– Limited irrigation (fossil fuels burned to power
irrigation)
• Restorasi (Pemulihan )Tanah
BAHAN ORGANIK TANAH
KANDUNGAN ,
JENIS-JENIS,
KARAKTERISTIKNYA
BENTUK-BENTUK KARBON DALAM TANAH
BAHAN
ORGANIK
TANAH
SUSUNAN JARINGAN TUMBUHAN
Karbon
11%
Air
75%
Padatan
25%
Oksigen
10%
Hidrogen
22%
Abu 2%
SUSUNAN BAHAN TUMBUHAN YG DITAMBAHKAN KE
TANAH
AIR 75%
Gula & Pati (1-5% )
Hemiselulose 10-30%
Selulose 20-50%
SUSUNAN UNSUR
Padatan 25%.
Hidrat Arang 60%
Karbon 44%
Hidrogen
8%
Abu
8%
Protein
10%
Lignin 20-30%
Lemak, lilin, tanin 1-8%.
Oksigen
40%
BAHAN ORGANIK TANAH
BO)T mencakup semua
komponen organik dari
tanah:
1. Residu segar
2. BO yang sedang
mengalami
dekomposisi
3. BO yang stabil
4. Organisme hidup
RESIDU SEGAR
1. Hingga 15% dari BO berupa residu segar
(biasanya <10)
2. Terdiri atas guguran dedaunan
3. Dapat dikenali beragam tipe seresah
tumbuhan
BO yang sedang mengalami
Dekomposisi
1. Biomasa tanaman ditransformasikan dari satu
senyawa organik menjadi senyawa organik lainnya
oleh organisme tanah
2. Organisme menghasilkan bahan-sisa, hasil
samping dan sel-sel tubuhnya
3. Senyawa-senyawa yang dilepaskan sebagai
limbah dari satu organisme dapat menjadi
makanan bagi organisme lainnya.
PERUBAHAN BAHAN ORGANIK YG DITAMBAHKAN KE
TANAH
I. Senyawa dalam jaringan tumbuhan segar
Sukar Dilapuk
Lignin
Minyak
Lemak
Resin,dll
II. Hasil intermedier dekomposisi
Senyawa tahan lapuk
Resin
Lilin
Minyak dan lemak
Lignin,dll
III. Hasil pelapukan dan tahan lapuk
Humus: kompleks koloidal
dari ligno-protein
Mudah dilapuk
Selulose
Zat pati
Gula
Protein,dll
Senyawa tidak tahan lapuk
Asam amino
Amida
Alkohol
Aldehide, dll
Hasil akhir yg sederhana
CO2 dan air
Nitrat
Sulfat
Fosfat,
Senyawa Ca,dll.
KOMPOSISI BAHAN ORGANIK
Soil microorganisms and fauna make up a relatively small portion of total soil organic
matter (1-8%).
Functions as an important catalyst for transformations of N and other nutrients
Majority of soil organic matter is contained in the nonliving component that includes
plant, animal and microbial debris and soil humus.
Cellulose generally accounts for the largest proportion of fresh organic material
•
decays rapidly
•
need N for decay
Lignin decomposes slowly
•
nutrients bound in lignin forms are not available for plant growth
•
lignin is insoluble in hot water and neutral organic solvents, but it is soluble in
alkali solutions
•
seldom find calcareous soils with high organic matter.
•
polysaccharides decompose rapidly in soils and serve as an immediate source of
C for microorganisms.
Parameter BIOMASA
Kadar air, %
N-total, %
P-total, %
C-total, %
C/N
C/P
Lignin, %
Polifenol, %
K, %
Ca, %
Mg, %
Asam-asam organik, g/kg:
Sitrat
Oksalat
Suksinat
Asetat
Malat
Butirat
Propionat
Phtalat
Benzoat
Salisilat
Galat
Sumber: Supriyadi, 2002.
Tithonia diversifolia
Tephrosia candida
70.2
2.1
0.3
38.5
19
128
9.8
3.3
2.1
1.3
0.6
62.1
1.7
0.1
33.9
21.1
305
12.1
5.1
1.7
1.2
0.2
32
11
48
17
775
49
31
20
69
0
0
86
30
0
16
15
0
0
19
56
12
0
APLIKASI BAHAN ORGANIK THD KANDUNGAN ASAM ORGANIK DLM TANAH ,
setelah 30 hari
Aplikasi BO
Konsentrasi asam dlm tanah Andisol (ppm):
Sitrat Oksalat Suksinat Asetat
Malat
Butirat
Total
T. candida
20
0
0
15
9.1
11
55
T. diversifolia
21
47
7.8
16
11
0
103
Campuran
13
15
3.6
7.2
26
5.9
70
Sumber: Supriyadi, 2002
BAHAN ORGANIK TANAH
• Soil organic matter =
– all living organisms
(microorganisms, earthworms,
etc),
– fresh residues (old plant roots,
crop residues, recently added
manures),
– well-decomposed residues
(humus).
•
The SOM content of agricultural
topsoil is usually in the range of 1 to
6%.
•
This amount is the result of all
additions and losses of SOM that
have occurred over the years.
•
Non-cultivated soils will have SOM
ranges between 3-10%
Citizen Science – Kansas State
BAHAN ORGANIK TANAH
BOT bersifat labile
1. it can decline rapidly if the soil environment
changes and renewable
2. it can be replenished by inputs of organic
material to the soil.
Labil = tidak stabil, mudah mengalami
perubahan secara kimia, fisika atau biologis.
BOT = Bahan Organik Tanah
• BOT = Humus
• Kandungannya:
– ~0 - 5% pada kebanyakan tanah
– Hingga 100% pada tanah organik (Histosol)
– Lebih tinggi kandungannya pada tanah-tanah
lembab
– Lebih rendah kandungannya pada tanahj-tanah
kering
– Pengolahan tanah dapat mengurangi BOT
• Luas permukaannya dan KTK sangat besar
• Kehilangan C dan N
Komposisi BOT
• Mayoritas: lignins dan proteins
– Also: hemicellulose, cellulose, ether and alcohol
soluble compounds
– “nonhumic” substances = “juicy” carbon that is
quickly digested
• (carbohydrates, proteins, peptides, amino acids, fats,
waxes, low MW acids)
• Kebanyakan BOT tidak larut air
Definisi
Cellulose
Lignin
= a practically indigestible compound which,
along with cellulose, is a major component
of the cell wall of certain plant materials,
such as wood, hulls, straws, etc.
Hemicellulose: A carbohydrate
resembling cellulose but more
soluble; found in the cell walls of
plants.
SIFAT & CIRI BOT
• Voids can trap
– Water
– Minerals
– Other organic molecules
• Hydrophobicity/hydrophilicity
• Reactivity
• H-bonding, chelation of metals
Fig 3.8
Gugus Fungsional & Muatan Listrik
• PZC ~ 3 (pH of zero charge)
• Up to 80% of CEC in soils is due to SOM
• Acid functional groups
– Carbonyls pKa < 5
– Quinones also pKa < 5
– Phenols pKa < 8
55% of SOM CEC?
30% of SOM CEC?
• SOM constitutes most of the buffering
capacity of soils
PROFIL TANAH
Lapisan tanah-atas (topsoil)
mengandung lebih banyak
bahan organik
dibandingkan dengan
lapisan di bawahnya
(subsoil).
Sumber:
ag.arizona.edu/pubs/garden/mg/so...i
ls.html
Organic Matter
Biomass
(living organisms)
CO2
(identifiable dead tissue)
Fungi
Earthworms
Bacteria
Soil Humus
(nonliving, nontissue decay products)
Humin
(insoluble)
Humic Acid
(insoluble in acid)
Fulvic Acid
(soluble)
degradation
Detritus (Plant Debris)
CADANGAN
BOT Aktif
BOT
Menekan Penyakit
Agregasi tanah
Suplai hara
Dekomposisi
BOT Stabil
KTK
Mikro-agregasi
BOT Total
DEGRADASI BOT: SIKLUS HARA
Biomass
Biomasa
Nutrient
Penyerapan
Incorporation
Hara
Detritur
(seresah
Detritus
(PlantTumbuhan)
Debris)
Pelepasan
Nutrient
Hara
Release
SoilHumus
Humus
Tanah
HUMUS
Gugus fungsional reaktif:
karboksil, hidroksil, fenolik
1. Kapasitas pertukaran
kation (anion) sangat besar
2. Kapasitas penyimpanan air
sangat besar
3. Membantu agregasi tanah
BAHAN ORGANIK TANAH
CARA MENGUKURNYA
Bagaimana mengukur BOT?
SOM is usually measured in the
laboratory as organic carbon,
Soil organic matter is estimated to
contain 50% organic carbon
(varies from 40 to 70%) with the
rest of the SOM comprising of
other elements (eg, 5% N, 0.5% P
and 0.5% S).
A conversion to SOM from a given
organic carbon analysis requires
that the organic carbon content be
multiplied by a factor of
2.00(1.00/0.50).
Thus, 2% SOM is about 1 % organic
carbon.
Testing for Soil Organic Carbon
UF/IFAS Extension Soil Testing Laboratory
Analisis substansi humik dalam tanah.
Scheme for the
isolation of humic
substances from soil
[Adapted from
Stevenson (1994)];
*California
Department of Food
and Agriculture
(CDFA) testing
process end point
Diunduh dari sumber: http://oceanagrollc.com/standard-humic-acid-testing-protocols-a-review/ …… 26/10/2012
ANALISIS BAHAN ORHANIK TANAH
1.
Soil
WalkleyAnalysis Black
Organic
Method
Matter
2.
3.
Jackson, M. L. 1958. Soil Chemical Analysis. 214221.2. Walkley, A. 1947. A Critical Examination of
a Rapid Method for Determination of Organic
Carbon in Soils - Effect of Variations in Digestion
Conditions and of Inorganic Soil Constituents.
Soil Sci. 63:251-257.
Walkley, A. and I. A. Black. 1934. An Examination
of Degtjareff Method for Determining Soil
Organic Matter and a Proposed Modification of
the Chromic Acid Titration Method. Soil Sci.
37:29-37.
Schollenberger, C. J. 1927. A Rapid Approximate
Method for Determining Soil Organic Matter. Soil
Sci. 24:65-68.
Diunduh dari sumber:
…… 26/10/2012
INDIKATOR BOT .
The content of organic matter of mineral horizons can be
estimated from the Munsell colour of a dry and/or moist
soil, taking the textural class into account. This estimation is
based on the assumption that the soil colour (value) is due to
a mixture of dark coloured organic substances and light
coloured minerals.
This estimate does not work very well in strongly coloured
subsoils. It tends to overestimate organic matter content in
soils of dry regions, and to underestimate the organic matter
content in some tropical soils. Therefore, the organic matter
values should always be locally checked as they only provide
a rough estimate.
Diunduh dari sumber: ftp://ftp.fao.org/agl/agll/docs/guidel_soil_descr.pdf …… 27/10/2012
Estimation of organic matter content based on Munsell soil colour.
Sand
. Note: If chroma is 3.5–6, add 0.5 to value; if chroma is > 6, add 1.0 to value.
Source: Adapted from Schlichting, Blume and Stahr, 1995.
Steps in the cycling of soil C and the formation of soil organic matter and
humus.
Diunduh dari sumber: http://www.soils.umn.edu/academics/classes/soil5611/content/OrganicMatter/ …… 27/10/2012
General flow of the
sequential SOM
fractionation procedure.
Diunduh dari sumber:
http://www.sciencedirect.com/science/article
/pii/S0146638002000128 …… 27/10/2012
BAHAN ORGANIK TANAH
FUNGSINYA
Komponen-komponen dari Sistem Manajemen Tanah-Berkelanjutan
Sumber: www.agnet.org/library/eb/473/
Hubungan antara Pembangunan Berkelanjutan dengan Manajemen Tanah
Berkelanjutan (Redrawn from Dumanski 1997)
Sumber: www.agnet.org/library/eb/473/
Sumber: www.agnet.org/library/eb/473/
Fungsi
BOT
Fungsi & Peranan Bahan Organik Tanah (Soil Organic Matter)
Fungsi Humus
• holds water and
nutrients;
• sticks together & helps
establish and maintain a
strong crumb structure
& thus reduce soil
erosion
•
provides some
nutrients (N & P) as it is
slowly decayed by
microbial activity,
• Buffers effects of
pesticides
• humus decomposes at
the rate of 2.5% per year
• Creates good soil “ Tilth”
• Coates the sand, silt,
clay particles making
them dark and the darker
the color, the greater the
amount of soil humus
present.
Humus = High
Medium
Low
BOT menjaga Sifat Olah Tanah
• Membantu
infiltrasi air
hujan dan
udara ke
dalam tanah
• Membantu
menahan air
• Mengurangi
erosi tanah
BOT = Kesehatan
Tanah
“If your soil clods can't pass the water test, change
your management practices. It will help your
bottom line as well as the soil.” – Ray Weil – Univ of
Maryland
• Measuring SOM is one step in
assessing overall soil quality or
soil health • measuring various key attributes
of soil organic matter quantity
and quality will give an indication
of the health of the soil.
• Or Look at the state of the soil
organisms in the soil.
• Or look at how well the soil
“Holds Together”.
Simple clod test: Healthy soil, at
left, holds together in water, while
poor soil falls apart.
Penggunaan Kualitas Tanah
• 1) Match use and
management of land to soil
capability, because improper
use of a soil can damage it
and the ecosystem.
• 2) Establish a baseline
understanding about soil
quality so that we can
recognize changes as they
develop.
• 3) Use baselines to
determine if soil quality is
deteriorating, stable, or
improving.
Kualitas tanah menjadi indikator
dari kesehatan ekosistem.
NatureWatch
Kualitas Tanah
http://www.directseed.org/soil_quality.htm
• Soil quality is the capacity of soils
within landscapes to sustain
biological productivity, maintain
environmental quality, and
promote plant and animal health.
• Protecting soil quality like
protecting air quality and water
quality should be fundamental
goal of our Nation’s
Poor
Good
Environmental Policy
http://www.nrsl.umd.edu/research/NRSLResearchAreaInfo.cfm?ID=14
KESEHATAN TANAH
•
•
Soil Health is the change
in Soil Quality over time
due to human use and
management or to natural
events.
Descriptive terms for Soil
Health
– Organic Matter - high
– Crop appearance =
green, healthy,lush
– erosion – Soil will not
erode
– earthworms – numerous
– infiltration – fast, no
ponding
– Compaction - minimal
Cornell researcher George Abawi describes soil health
strategies at an Onion Council field day in Wayne
County, N.Y.Photo by Carol R. MacNeil.
In Vernon and surrounding counties are the largest
concentration of organic farmers in Wisconsin.
Kontribusi Biota Tanah pada Dekomposisi BOT
Sumber: www.ipm.msu.edu/new-ag/issues06/7-26.htm
Perubahan Kandungan Bahan Organik Tanah (jangka panjang)
pada berbagai kondisi pengelolaan tanah
Sumber: www.agnet.org/library/eb/473/
Soil processes influence carbon sequestration and transport. The dynamics of carbon
transformations and transport in soil are complex and can result in sequestration in the soil as
organic matter or in groundwater as dissolved carbonates, increased emissions of CO2 to the
atmosphere, or export of carbon in various forms into aquatic systems (DOE, 1999).
Sumber: www.climatescience.gov/Library/s...hap7.htm
BAHAN ORGANIK TANAH:
FAKTOR YANG
MEMPEMNGARUHI
BOT
Faktor yang mempengaruhi
BOT
•
•
•
•
•
1) Kind of parent materials (texture
primarily), climate, slope, and
management practices that exist. (Sandy
= Low & Clay = High)
2) Climate: PMs that have not lost their
nutrients from excessive rainfall
(leaching), and areas where temperature
and water are adequate will have high
SOM.
3) Management practices that affect crop
biomass (yield and straw) production
(water, fertilizer, variety), residue
maintenance (equipment, harvest), and
litter (wind) will also affect SOM content.
4) As dry matter production increases,
SOM increases.
5) However, only that which remains after
harvest along with root biomass will
influence long-term SOM content.
Morrow Plots – Why the difference in SOM?
manure, lime and phosphorus (MLP)
Established in 1876 the Morrow Plots are the oldest agronomic experiment fields in the United States. They include
the longest-term continuous corn plot in the world. Located near the center of the University of Illinois' Urbana
campus.
Fraksi Aktif dari BOT
• 10 to 30% of the soil
organic matter (active
fraction) is responsible
for maintaining soil
microorganisms.
• The active fraction of
organic matter is most
susceptible to soil
management practices.
(Inactive = humus)
ACTIVE
Penambahan BO segar
• In a soil which at
first has no readily
decomposable
materials, adding
fresh tissue under
favorable
conditions:
• 1) immediately
starts rapid
multiplication of
bacteria, fungi, and
actinomycetes,
• 2) which are soon
actively
decomposing the
fresh tissue.
ADDED
BOT SEGAR
• as most readily
available energy
sources are used
up,
microorganisms
again become
relatively inactive,
• leaving behind a
dark mixture
usually referred to
as humus – a stable
organic compound
HUMUS : Bahan Organik yang Stabil
• Thus, soil organic
compounds become
stabilized and
resistant to further
changes by
microorganisms
• Stabilized organic
matter acts like a
sponge and can
absorb six times its
weight in water
HUMUS
• Newly-formed humus=
• a) combination of
resistant materials
from the original plant
tissue,
• b) compounds
synthesized as part of
the microorganisms'
tissue which remain as
the organisms die.
(Fulvic and Humic
Acid)
• humus is mostly
resistant to further
microbial attack- N
and P are protected
from ready solubility
Leaf Humus
BAGAIMANA MENINGKATKAN KANDUNGAN BOT
1.
No-till management practices (10 yrs no-tillage with corn, OC in surface 30 cm
increased by 0.25% (Blevins et al. 1983).
2.
N rates in excess of that required for maximum yields result in increased
biomass production (decreased harvest index values e.g., unit grain produced
per unit dry matter) . Increased amounts of carbon from corn stalks, wheat
stems,
3.
Fertility of forest and grassland soils in North America has declined
significantly as soil organic matter was mined by crop removal without
subsequent addition of plant and animal manures (Doran and Smith, 1987).
4.
For thousands of years, organic matter levels were allowed to increase in
these native prairie soils since no cultivation was ever employed.
5.
As soil organic matter levels declined, so too has soil productivity while
surface soil erosion losses have increased. Because of this, net mineralization
of soil organic nitrogen fell below that needed for sustained grain crop
production (Doran and Smith, 1987).
Available Mineral N, kg ha-1
Untuk mempertahankan hasil tanaman, diperlukan penambahan Hara N dari
pupuk, rabuk kandang dan Tanaman legume manures or legumes are required
75
Net N lost from soil humus
Net N mineralized during fallow
50
Nitrogen mineralized
from straw and roots
25
Cereal crop requirement
( 17 Mg ha-1 )
0
0
20
40
60
80
100
Years of Cultivation
Influence of cultivation time on relative mineralization from soil humus and wheat
residue. (From Campbell et al. (1976)).
Should the decline in years 1-5 be greater?
KEHILANGAN
BOT
When the prairie soils of Oklahoma were first cultivated in the late 1800s,
there was approximately 4.0% soil organic matter in the surface 1
foot.
Within that 4.0% organic matter, there were over 8000 lb of N/acre.
Following more than 100 years of continuous cultivation, soil organic matter
has now declined to less than 1%.
Within that 1% organic matter, only 2000 lb of N/acre remains.
N removal in the Check (no fertilization) plot of the Magruder Plots
20 bu/acre * 60 lb/bu * 100 years = 120000 lbs
120000 lbs * 2%N in the grain = 2400 lbs N/acre over 100 years
8000 lbs N in the soil (1892)
-2000 lbs N in the soil (1992)
-2400 lbs N removed in the grain
+1000 lbs N (10 lb N/ac/yr added via rainfall in 100 years)
=4600 lbs N unaccounted
KEHILANGAN
BOT
N removal in the Check (no fertilization) plot of the Magruder Plots
20 bu/acre * 60 lb/bu * 100 years = 120000lbs
120000 lbs * 2%N in the grain = 2400 lbs N/acre over 100 years
8000 lbs N in the soil (1892)
-2000 lbs N in the soil (1992)
-2400 lbs N removed in the grain
+1000 lbs N (10 lb N/ac/yr added via rainfall in 100 years)
= 4600 lbs N unaccounted
Plant N Loss
Denitrification
EFEK PENGELOLAAN TANAH thd BOT
Effects that management systems will have on soil organic matter and the resultant
nutrient supplying power of the organic pools are well known. Various
management variables and their effect on soil organic matter are listed:
Pengelolaan BO
Efeknya
___________________________ __________
1)
tillage
+/-
conventional
-
zero
+
2) soil drainage
+/-
3) crop residue placement
+/-
4) burning
-
5) use of green manures
+
6) animal wastes and composts
+
7) nutrient management
+/-
excess N
+
80
60
C:N
Net Immobilization
40
Net Mineralization
20
0
4 to 8 Weeks
NO 3-
CO 2 Evolution
Amount
C O2
Time
New NO3-
Level
Perubahan Kadar N Jerami yang sedang mengalami dekomposisi
(From Alexander, 1977).
1.75
40
1.5
30
1.25
1
20
0.75
0.5
0
30
60
Days
90
10
120
C:N ratio of rotting tissue
Nitrogen in rotting tissue, percent
2
Manure Applied
1
Mineral N
Mineral N
Mineral N
Mineral N
2
Microbial tissue
Microbial tissue
0
3
Time
0
Straw Applied
Time
protein
exhausted
4
Fallow
Mineral N
Mineral N
Microbial tissue
Cropped
Mineral N
0
sugar
exhausted
0
4
Time (weeks)
14
Time
Perubahan kandungan N-tanah merupakan fungsi waktu,
penambahan rabuk dan jerami
BAHAN ORGANIK TANAH:
DEKOMPOSISINYA
Daur-Ulang Unsur Hara.
Bakteri
Diunduh dari sumber:
Fungi
http://www.safs.msu.edu/soilecology/soilbiology.htm…… 26/10/2012
Most of the N is in the soil organic matter.
Diagram of N Cycle
Sumber: www.soils.umn.edu/academics/clas...hap2.htm
PROSES DEKOMPOSISI BAHAN ORGANIK
Residu bahan organik segar terdiri atas bangkai mikroba tanah,
serangga dan cacing, akar-tua tumbuhan, residu tanaman, dan pupuk
kandang/kompos/pupuk hijau.
Biomasa tanaman mengandung senyawa karbon kompleks yang
berasal dari dinding sel (cellulose, hemicellulose, etc.). Rantai karbon
membentuk “backbone” dari molekul organik.
Rantai karbon ini, dengan beragam jumlah atom oksigen, H, N, P
dan S, merupakan basis dari molekul asam amino dan gula, dan
molekul lain yang lebih kompleks.
Laju dekomposisi senyawa organik ini tergantung pada struktur
kimianya, dekomposisi cepat (sugars, starches and proteins), lambat
(cellulose, fats, waxes and resins) atau sangat lambat (lignin).
Diunduh dari sumber: http://www.fao.org/docrep/009/a0100e/a0100e05.htm#TopOfPage …… 26/10/2012
PROSES DEKOMPOSISI BAHAN ORGANIK
Selama proses dekomposisi BO, mikroba mengubah struktur karbon
dari bahan segar menjadi produk-produk karbon dalam tanah.
Ada banyak macam molekul organik dalam tanah. Sebagian adalah
molekul sederhana yang disintesis langsung dari tanaman atau
organisme lainnya. Senyawa ini sederhana, seperti gula, amino acids,
dan sellulose yang mudah dikonsumsi oleh organisme.
Senyawa organik lainnya, seperti resins dan lilin juga berasal
langsung dfari tanaman, tetapi lebih sulit dilapuk oleh organisme
tanah.
Humus merupakan hasil dari tahap-tahap akhir dalam dekomposisi
BO. Substansi humuk ini strukturnya kompleks, sehingga tidak
dapat digunakan sebagai sumber energi oleh mikroba tanah, dan
tetap berada dalam tanah selama periode waktu yang lama.
Diunduh dari sumber: http://www.fao.org/docrep/009/a0100e/a0100e05.htm#TopOfPage …… 26/10/2012
PROSES DEKOMPOSISI BAHAN ORGANIK
Mekanisme
pembentukan
substansi
humik dlaam
tanah.
Diunduh dari sumber:
http://www.humet.com/acatalog/humifulvatescience.html…… 26/10/2012
PELAPUKAN (DEKOMPOSISI) BAHAN ORGANIK TANAH
Laju Dekomposisi
1. Gula,pati,protein sederhana
2. Protein kasar
3. Hemiselulose
4. Selulose
5. Lignin,lemak, lilin, dll.
(cepat dilapuk)
(Lambat dilapuk)
Reaksi yg dialami BOT :
1. Reaksi oksidasi ensimatik yang menghasilkan CO2, H2O dan panas
2. Unsur-unsur fungsional, N, P dan S dibebaskan ke tanah, atau
digunakan dalam reaksi-reaksi lainnya dalam siklus unsur hara
3. Senyawa-senyawa organik yang tahan lapuk akan terbentuk dari
bahan organik asalnya atau dari hasil bentukan jasad renik tanah
DEKOMPOSISI = Proses pembakaran
Dalam kondisi tanah aerobik, proses dekomposisi bahan organik merupakan
proses oksidasi ensimatik.
Oksidasi ensimatik
- (C,4H) + O2
CO2 + 2 H2O + energi
Senyawa organik
C dan H
Reaksi-reaksi lainnya terjadi secara simultan, melibatkan unsur-unsur lain selain
C dan H.
Reaksi yg dialami PROTEIN :
Protein + lignin
ligno-protein
Protein
HUMUS
Amida + Asam Amino
Bakteri, Fungi,
Aktinomisetes
Asam organik + -NH2
Asam amino
Amida
hidrolisis ensimatik
Asam amino
CO2 + NH4+
NO3-
DEKOMPOSISI BOT vs. SIKLUSNYA
BO ditambahkan ke tanah
Jasad renik menyerang
senyawa yg mudah lapuk
(gula, pati,dll)
Pembebasan CO2 & H2O
Terbentuk senyawa
yang sukar dilapuk
HUMUS
Jumlah jasad renik
CO2 & H2O
Senyawa dlm
jaringan asli
Tingkatan humus
tanah
Senyawa jasad
BO segar
waktu
Humus tanah
HUMUS
ENERGI BAHAN ORGANIK TANAH
Bahan organik berfungsi sebagai Sumber karbon dan sumber energi bagi
jasad renik tanah
Bahan organik tumbuhan mengandung energi 4 - 5 kcal per satu gram
bahan kering
Mis: 10 pupuk kandang = 2.5 ton bahan kering == 9-11 juta
kcal energi laten.
Tanah yg mengandung 4% BOT mempunyai 170-200 juta kcal energi
potensial setiap hektar lapisan olah, ini setara dengan 20-25 ton batu
bara
Energi laten ygtersimpan dalam BOT, sebagian digunakan oleh jasad
renik dan sebagian dilepaskan sebagai panas.
Kalau tanah diberi bahan organik (pupuk kandang atau lainnya),
sejumlah energi panas akan dibebaskan ke atmosfer.
DEKOMPOSISI BAHAN ORGANIK
• Earthworms
– Mix fresh organic materials into the
soil
– Brings organic matter into contact
with soil microorganisms
Corn leaf pulled into
nightcrawler burrow
Millepede
• Soil insects and other arthropods
– Shred fresh organic material into
much smaller particles
Ants
– Allows soil microbes to access all
parts of the organic residue
DEKOMPOSISI BAHAN ORGANIK
• Bacteria
– Population increases
rapidly when organic
matter is added to soil
– Quickly degrade simple
compounds - sugars,
proteins, amino acids
– Have a harder time
degrading cellulose, lignin,
starch
– Cannot get at easily
degradable molecules that
are protected
Bacteria on fungal strands
Spiral bacteria
Rod bacteria
DEKOMPOSISI BAHAN ORGANIK
• Fungi
–Grow more slowly and
efficiently than bacteria
when organic matter is
added to soil
Tree trunk
rotted by fungi
–Able to degrade more
complex organic molecules
such as hemicellulose,
starch, and cellulose.
–Give other soil
microorganisms access to
simpler molecules that
were protected by cellulose
or other complex
Fairy ring
compounds.
Fungus on poplar leaf
Soil fungus
Fungi dan Struktur Tanah
Hifa Fungi (benang) membantu memegang granula tanah
Eksudat Fungi (goo) membantu merekat partikel tanah
Active Fungi Present –
Soil structure is maintained when
immersed in water
Fungi absent Soil structure is not maintained
when immersed in water
DEKOMPOSISI BAHAN ORGANIK
• Actinomycetes
–The cleanup crew
–Become dominant in the final stages of
decomposition
–Attack the highly complex and decay resistant
compounds
• Cellulose
• Chitin (insect shells)
• Lignin
• Waxes
DEKOMPOSISI BAHAN ORGANIK
• Protists and nematodes,
the predators
– Feed on the primary
decomposers (bacteria,
fungi, actinomycetes)
– Release nutrients (nitrogen)
contained in the bodies of
the primary decomposers
Rotifer
Amoeba
Bacteria-feeding nematode
Predatory nematode
Dekomposisi Bahan Organik:
Daur ulang Carbon dan Nitrogen
During each cycle of
degradation about 2/3 of the
organic carbon is used for
energy and released as carbon
dioxide (CO2)
CO2
Plant litter
During each cycle of
degradation about 1/3 of the
organic carbon is used to build
microbial cells or becomes
part of the soil organic matter
CO2
Bacteria, Fungi
Soil organic matter
Nematodes, protists, humus
Dekomposisi Bahan Organik:
C/N ratio
Litter C/N
ratio
around
24:1
CO2
C/N
ratio
8:1
Average C/N ratio of
bacteria and fungi is
8:1
2/3 of carbon
released as CO2
Microbial C/N ratio is
maintained at 8:1 with no
uptake or release of N
Dekomposisi Bahan Organik:
C/N ratio
Litter C/N
ratio
around
90:1
Soil N
CO2
C/N
ratio
30:1
Average C/N ratio of
bacteria and fungi is
8:1
Immobilisasi
2/3 of carbon
released as CO2
Microbial C/N ratio is
maintained at 8:1 by
taking up N from soil
Dekomposisi BO dan C/N-ratio
C/N ratio
seresah
tanaman
sekitar 9:1
CO2
C/N
ratio
3:1
Rataan C/N ratio
bakteri dan fungi
8:1
Mineralisasi
2/3 carbon
dibebaskan
sebagai CO2
Microbial C/N ratio is
maintained at 8:1 by
releasing N to the soil
N-tanah
Bahan organik dalam tanah tidak homogen
Scientists describe 3 pools of soil organic matter
Active SOM
1 – 2 yrs
C/N ratio 15 – 30
• Recently deposited organic material
• Rapid decomposition
• 10 – 20% of SOM
Slow SOM
15 – 100 yrs
C/N ratio 10 – 25
Passive SOM
500 – 5000 yrs
C/N ratio 7 – 10
• Intermediate age organic material
• Slow decomposition
• 10 – 20% of SOM
• Very stable organic material
• Extremely slow decomposition
• 60 – 80% of SOM
• There is a constant turnover of organic material in soil.
• The quantity of SOM depends on the balance between inputs and losses of
organic material
Sisa tanaman
Akart-akar
Rabuk
Kompos
Inputs
Dekomposisi
(CO2)
Bahan organik tanah
BOT
Kehil;angan
Erosi
Kalau kehilangan meningkat dan intputnya konstan, maka
BOT akan menurun
Crop Residues
Crop Roots
Manure
Compost
Inputs
Soil Organic Matter
Decomposition
(CO2)
Losses
Erosion
Kalau Input meningkat dan Kehilangannya konstan, maka
BOT akan meningkat
Crop Residues
Crop Roots
Manure
Compost
Inputs
Decomposition
(CO2)
Soil Organic Matter
Losses
Erosion
BOT tidak akan secara kontinyu meningkat atau menurun
When inputs or losses are changed, SOM quantity changes to a
different level and a new steady state condition is reached.
SOM level
SOM in virgin soil
Corn-oats-clover
rotation plus
manure application
Management
change
imposed
New steady
state SOM
level
Steady state SOM after
years of continuous
corn cultivation
1875
1955
Years of cultivation
2005
BOT BERSIFAT DINAMIS
Laju Dekomposisi BOT dipengaruhi oleh:
1.
Environmental Conditions
•
•
•
•
•
•
Temperature
Moisture
Aeration (oxygen)
Soil texture
Soil pH
Soil fertility
2.
Quality of added Organic
Material
• C/N ratio
• Composition/Age
• Physical properties and
placement
• Fresh vs. “processed”
HASIL SEDERHANA DEKOMPOSISI
B.O.T.
Proses dekomposisi ensimatik akan menghasilkan berbagai senyawa anorganik
sederhana. Bentuk-bentuk an-organik ini tersedia bagi tanaman dan mudah
hilang dari tanah.
.
Hasil-hasil proses dekomposisi ensimatik:
Karbon
: CO2, CO3=, HCO3-, CH4, C
Nitrogen
: NH4+, NO2-, NO3-, gas N2
Belerang
: S, H2S, SO3=, SO4=, CS2
Fosfor
: H2PO4-, HPO4=
Lainnya
: H2O, O2, H2, H+, OH-, K+, Ca++, Mg++, …….
Perubahan konsentrasi asam organik dalam tanah
Konsentrasi asam organik, ppm
70
Tanah ditanami T. diversifolia
Tanah ditanami T. candida
Tanah tanpa tanaman
0
Waktu : 0-90 hari
Sumber: Supriyadi, 2002
APLIKASI BAHAN ORGANIK thd JERAPAN-P dan KONSENTRASI P -TANAH
ANDISOL, setelah 30 hari
Jerapan P (%)
Konsentrasi P (ppm)
T. candida
Campuran
Campuran
T. diversifolia
T. candida
T. diversifolia
Waktu (0-30 hari)
Sumber: Supriyadi, 2002
Waktu (0-30 hari)
APLIKASI BAHAN ORGANIK THD KANDUNGAN P-TANAH
Andisol, setelah inkubasi 30 hari
Aplikasi BO
P-labil (ppm)
Kontrol
Akar + tajuk T.diversifolia
Tajuk T.diversifolia
Akar T.diversifolia
Akar + tajuk T. candida
Tajuk T. candida
Akar T. candida
Pupuk SP-36
24.38
40.07
31.35
17.94
26.91
26.48
18.57
32.17
Sumber: Supriyadi, 2002
Jerapan P (%)
95.03
88.97
89.58
90.44
90.37
90.66
90.91
89.79
P-tersedia
(ppm)
3.01
6.10
5.81
3.80
5.10
4.88
3.54
5.52
APLIKASI BAHAN ORGANIK THD pH dan KTK TANAH Andisol, setelah inkubasi 30
hari
Aplikasi BO
pH(H2O)
pH(KCl)
KTK
Kontrol
Tithonia 25 kg
Tithonia 50 kg
Tithonia 75 kg
Tephrosia 25 kg
Tephrosia 50 kg
Tephrosia 75 kg
Campuran 25 kg
Campuran 50 kg
Campuran 75 kg
5.4
5.5
5.6
5.7
5.6
5.6
5.6
5.6
5.6
5.7
4.9
4.7
4.7
4.6
4.7
4.7
4.6
4.7
4.6
4.6
33.1
35.1
36.5
37.4
36.2
37.1
37.1
35.8
36.8
37.1
Sumber: Supriyadi, 2002
• Adequate levels of SOM
can be maintained with:
– proper fertilization,
– crop rotations, and
tillage practices
– Returning crop
residues to the soil.
Degradasi Residu Tanaman dan Pembentukan BOT
Sumber: www.microbiologyprocedure.com/or...mus.html
Dekomposisi seresah daun Miscanthus sinensis.
Original component left, grams
100
Total
organic
matter
80
60
40
Cellulose
20
Lignin
Hemicellulose
0
0
1
2
3
Years
…. Diunduh 15/2/2012
4
5
Dekomposisi Bahan Organik
1.
As decomposition proceeds, water soluble fractions (sugars, starch, organic
acids, pectins and tannins and array of nitrogen compounds) readily utilized
by microflora.
2.
Ether and alcohol-soluble fractions (fats, waxes, resins, oils), hemicelluloses
and cellulose decrease with time as they are utilized as carbon and energy
sources.
3.
Lignin, persists and can accumulate in the decaying biomass because of its
resistance to microbial decomposition.
4.
Decomposition rates of crop residues are often proportional to their lignin
content and some researchers have suggested that the lignin content may be
a more reliable parameter for predicting residue decomposition rates than the
C:N ratio.
5.
Vigil and Kissel (1991) included the lignin-to-N ratio and total soil N
concentration (in g/kg) as independent variables to predict potential N
mineralization in soil. They also noted that the break point between net N
mineralization and net immobilization was calculated to be at a C/N ratio of 40.
The carbon cycle revolves around CO2, its fixation and regeneration.
Chlorophyll-containing plants utilize CO2 as their sole carbon source and the carbonaceous matter
synthesized serves to supply the animal world with preformed organic carbon.
Without the microbial pool, more carbon would be fixed than is released, CO2 concentrations in the
atmosphere would decrease and photosynthesis rates would decrease.
Pl ant-carbon
A
B
Ani m al -carbon
Soi l organi c matter
C
M i crobi al cel l s, decayed resi dues
D
E
Carbon di oxi de
A. Photosynthesi s
B. Respi rati on, pl ant
C. Respi rati on, ani mal
D. Autotropi c mi croorgani sms
E. Respi rati on, m i crobi al
The c a rbon c yc le
C/N dan Dekomposisi Bahan Organik
C:N Ratios as Related to Organic Matter Decomposition
In general, the following C:N ratios are considered to be a general rule of thumb in terms of what is
expected for immobilization and mineralization.
C:N Ratio
Effect
30:1
immobilization
<20:1
mineralization
20-30:1
immobilization = mineralization
1.
C:N ratios say nothing about the availability of carbon or nitrogen to microorganisms
2.
Why? What makes up the carbon (C) component
3.
In tropical soils, significantly higher proportions of lignin will be present in the organic matter
4.
Even though the percent N within the organic matter may be the same, it would be present in
highly stable forms that were resistant to decomposition.
5.
Therefore, mineralization rates in organic matter that contain high proportions of lignin will be
much smaller
6.
C:N ratios discussed were generally developed from data obtained in temperate climates.
7.
Therefore their applicability to tropical soils is at best minimal.
Dekomposisi Bahan Organik
Decomposition of Organic Matter (Mineralization)
1. percent organic matter
2. organic matter composition
3. cultivation (crop, tillage, burning)
4. climate (moisture, temperature)
5. soil pH
6. N management (fertilization)
7. soil aeration
Rapid increase in the number of heterotrophic organisms accompanied by the evolution
of CO2 (initial stages)
Wide C:N ratio of fresh material is wide = net N immobilization
As decay proceeds, C:N ratio narrows & energy supply of C diminishes.
Addition of materials with >1.5 to 1.7% N need no supplemental fertilizer N or soil N to
meet demands of microorganisms during decomposition
‘Demands of the microorganisms' discussed first, disregarding plant N needs
Adding large amounts of oxidizable carbon from residues with less than 1.5% N creates a
microbiological demand for N, immobilize residue N and inorganic soil N
Addition of fertilizer N to low N residues accelerates rate of decomposition (Parr and
Papendick, 1978).
C/N ratio Bahan Organik
1. 1000+yrs prior to the time cultivation was initiated, C and N had built up in native
prairie soils.
2. C:N ratio was wide, reflecting conditions for immobilization of N.
3. Combined influence of tillage and the application of additional organic materials
(easily decomposable wheat straw and/or corn stalks)
4. Cultivation alone unleashed a radical decomposition of the 4% organic matter in
Oklahoma soils.
5. Easily decomposable organic materials added back to a cultivated soil, increases CO2
evolution and NO3 is initially immobilized.
6. Within one yearly cycle in a temperate climate, net increase in NO3 is reflected via
mineralization of freshly added straw/stalks and native organic matter pools.
7. Percent N in added organic material increases while the C:N ratio decreases
8. In order for this to happen, some form of carbon must be lost from the system. In this
case CO2 is being evolved via the microbial decomposition of organic matter.