MK. DASAR ILMU TANAH BAHAN ORGANIK TANAH Oleh: Soemarno JURUSAN TANAH FPUB NOP. 2013
Feb 24, 2016
MK. DASAR ILMU TANAH
BAHAN ORGANIK TANAHOleh:
Soemarno
JURUSAN TANAH FPUB NOP. 2013
SIKLUS KARBONTanaman
HewanCO2
Pupuk KandangReaksi
dalam Tanah
CO2Aktivitas Mikroba
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
BAHAN ORGANIK TANAH
BENTUK-BENTUK KARBON DALAM TANAH
SUSUNAN JARINGAN TUMBUHAN
Air
75%
Padatan
25%
Karbon11%
Oksigen10%
Hidrogen22%
Abu 2%
SUSUNAN BAHAN TUMBUHAN YG DITAMBAHKAN KE TANAH
AIR 75%
Padatan 25%.
Hidrat Arang 60%
Protein 10%
Lignin 20-30%
Karbon 44% Hidrogen
8%Abu8%
Oksigen 40%
Lemak, lilin, tanin 1-8%.
Gula & Pati (1-5% )Hemiselulose 10-30%Selulose 20-50%
SUSUNAN UNSUR
BAHAN ORGANIK TANAHBO)T mencakup semua komponen organik dari
tanah:
1. Residu segar2. BO yang sedang
mengalami dekomposisi
3. BO yang stabil4. Organisme hidup
RESIDU SEGAR
1. Hingga 15% dari BO berupa residu segar (biasanya <10)
2. Terdiri atas guguran dedaunan3. 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 Mudah dilapuk
Lignin SeluloseMinyak Zat patiLemak GulaResin,dll Protein,dll
II. Hasil intermedier dekomposisi Senyawa tahan lapuk Senyawa tidak tahan lapuk
Resin Asam aminoLilin AmidaMinyak dan lemak AlkoholLignin,dll Aldehide, dll
III. Hasil pelapukan dan tahan lapuk Hasil akhir yg sederhanaHumus: kompleks koloidal CO2 dan airdari ligno-protein Nitrat
SulfatFosfat,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 decayLignin 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 Tithonia diversifolia Tephrosia candida
Kadar air, % 70.2 62.1N-total, % 2.1 1.7P-total, % 0.3 0.1C-total, % 38.5 33.9 C/N 19 21.1C/P 128 305 Lignin, % 9.8 12.1Polifenol, % 3.3 5.1K, % 2.1 1.7Ca, % 1.3 1.2Mg, % 0.6 0.2Asam-asam organik, g/kg:Sitrat 32 86Oksalat 11 30Suksinat 48 0Asetat 17 16Malat 775 15Butirat 49 0Propionat 31 0Phtalat 20 19Benzoat 69 56Salisilat 0 12Galat 0 0
Sumber: Supriyadi, 2002.
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
• 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.
BAHAN ORGANIK TANAH
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
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.
Cellulose
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
• SOM constitutes most of the buffering capacity of soils
55% of SOM CEC?
30% of SOM CEC?
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
PROFIL TANAH
CO2 Detritus (Plant Debris)
Fungi EarthwormsBacteria
Soil Humus
Organic Matter
Biomass
Humin(insoluble)
Humic Acid(insoluble in acid)
Fulvic Acid(soluble)
degr
adat
ion
(nonliving, nontissue decay products)
(identifiable dead tissue)
(living organisms)
CADANGAN BOT
BOT Aktif
BOT Total
Dekomposisi
BOT StabilKTK
Mikro-agregasi
Menekan PenyakitAgregasi tanahSuplai hara
Soil Humus
DEGRADASI BOT: SIKLUS HARA
Biomass
Detritus (Plant Debris)
Nutrient Release
NutrientIncorporation
Biomasa
Humus Tanah
Detritur (seresah Tumbuhan)
Pelepasan Hara
Penyerapan Hara
Gugus fungsional reaktif: karboksil, hidroksil, fenolik
HUMUS
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 CarbonUF/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
Diunduh dari sumber: …… 26/10/2012
Soil Analysis - Organic Matter
Walkley-Black Method
1. Jackson, M. L. 1958. Soil Chemical Analysis. 214-221.2. 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.
2. 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.
3. Schollenberger, C. J. 1927. A Rapid Approximate Method for Determining Soil Organic Matter. Soil Sci. 24:65-68.
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.
. 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.
Sand
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 & Peranan Bahan Organik Tanah (Soil Organic Matter)
Fungsi BOT
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
• 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”.
“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
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• 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 Environmental Policy
http://www.directseed.org/soil_quality.htm
http://www.nrsl.umd.edu/research/NRSLResearchAreaInfo.cfm?ID=14
Poor Good
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 BOTSumber: 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.
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.
manure, lime and phosphorus (MLP)
Morrow Plots – Why the difference in SOM?
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
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).
BAGAIMANA MENINGKATKAN KANDUNGAN BOT
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?
0
25
50
75
0 20 40 60 80 100
Nitrogen mineralizedfrom straw and roots
Net N lost from soil humus
Net N mineralized during fallow
Ava
ilabl
e M
iner
al N
, kg
ha-1
Cereal crop requirement( 17 Mg ha )-1
Years of Cultivation
Untuk mempertahankan hasil tanaman, diperlukan penambahan Hara N dari pupuk, rabuk kandang dan Tanaman legume manures or legumes are required
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 Plots20 bu/acre * 60 lb/bu * 100 years = 120000 lbs120000 lbs * 2%N in the grain = 2400 lbs N/acre over 100 years8000 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 = 120000lbs120000 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 LossDenitrification
KEHILANGAN 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 +
EFEK PENGELOLAAN TANAH thd BOT
60
40
20
0
Net Mineralization
C:N
Time
CO Evolution2NO 3-
CO 2
80
Net Immobilization
3-New NO Level
Amount
4 to 8 Weeks
Kultivasi & Penambahan Jerami, Immobilisasi N & mineralisasi N, Pelepasan CO2
0.5
0.75
1
1.25
1.5
1.75
2
0 30 60 90 12010
20
30
40
Nitrog
en in
rottin
g tiss
ue, p
ercen
t
Days
C:N ra
tio of
rottin
g tiss
ue
Perubahan Kadar N Jerami yang sedang mengalami dekomposisi (From Alexander, 1977).
Time
Microb ial t issue
Mineral N
Minera
l N
0
1
Minera
l N
0 Time proteinexhausted
Microb ial t issu e
Mineral N2Manure App lied
Minera
l N
0
Time
Microbial t issue
Mineral N
sugarexhausted
3 Straw App lied
Time (weeks)0 4 14
Minera
l N
Fallow
Cropped
4
Perubahan kandungan N-tanah merupakan fungsi waktu, penambahan rabuk dan jerami
BAHAN ORGANIK TANAH:
DEKOMPOSISINYA
Daur-Ulang Unsur Hara.
Diunduh dari sumber: http://www.safs.msu.edu/soilecology/soilbiology.htm…… 26/10/2012
FungiBakteri
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
Diunduh dari sumber: http://www.humet.com/acatalog/humifulvatescience.html…… 26/10/2012
Mekanisme pembentukan
substansi humik dlaam
tanah.
PELAPUKAN (DEKOMPOSISI) BAHAN ORGANIK TANAH
Laju Dekomposisi
1. Gula,pati,protein sederhana (cepat dilapuk)2. Protein kasar3. Hemiselulose4. Selulose5. Lignin,lemak, lilin, dll. (Lambat dilapuk)
Reaksi yg dialami BOT :
1. Reaksi oksidasi ensimatik yang menghasilkan CO2, H2O dan panas2. Unsur-unsur fungsional, N, P dan S dibebaskan ke tanah, atau digunakan dalam reaksi-reaksi lainnya dalam siklus unsur hara3. Senyawa-senyawa organik yang tahan lapuk akan terbentuk dari bahan organik asalnya atau dari hasil bentukan jasad renik tanah
DEKOMPOSISI = Proses pembakaranDalam 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 HUMUS
Protein Amida + Asam AminoBakteri, Fungi,
Aktinomisetes
Asam organik + -NH2 Asam amino
Amida hidrolisis ensimatikAsam 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 Tingkatan humus jaringan asli tanah
Senyawa jasad Humus tanah BO segar waktu HUMUS
ENERGI BAHAN ORGANIK TANAH
Bahan organik berfungsi sebagai Sumber karbon dan sumber energi bagi jasad renik tanahBahan organik tumbuhan mengandung energi 4 - 5 kcal per satu gram bahan keringMis: 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
Ants
• Soil insects and other arthropods–Shred fresh organic material
into much smaller particles–Allows soil microbes to
access all parts of the organic residue
• 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
–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 compounds.
Soil fungus
Fungus on poplar leaf
Tree trunk rotted by
fungi
Fairy ring
DEKOMPOSISI BAHAN ORGANIK
Fungi dan Struktur Tanah
Hifa Fungi (benang) membantu memegang granula tanahEksudat Fungi (goo) membantu merekat partikel tanah
Fungi absent -Soil structure is not
maintained when immersed in water
Active Fungi Present –Soil structure is maintained
when immersed in water
•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
Amoeba
Bacteria-feeding nematode
Predatory nematodeRotifer
DEKOMPOSISI BAHAN ORGANIK
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)
Bacteria, FungiSoil organic matter Nematodes, protists, humus
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
Average C/N ratio of bacteria and fungi is
8:1
Litter C/N ratio
around 24:1
CO2
C/N ratio 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
2/3 of carbon released as CO2
Average C/N ratio of bacteria and fungi is
8:1
Litter C/N ratio
around 90:1
CO2
C/N ratio 30:1
Immobilisasi
Soil N
Microbial C/N ratio is maintained at 8:1 by taking up N from soil
Dekomposisi Bahan Organik:C/N ratio
Dekomposisi BO dan C/N-ratio
Rataan C/N ratio bakteri dan fungi
8:1
C/N ratio seresah tanaman sekitar
9:1
CO2
C/N ratio 3:1
2/3 carbon dibebaskan sebagai CO2
Mineralisasi N-tanah
Microbial C/N ratio is maintained at 8:1 by releasing N to the soil
Bahan organik dalam tanah tidak homogenScientists describe 3 pools of soil organic matter
Passive SOM500 – 5000 yrs
C/N ratio 7 – 10
Active SOM1 – 2 yrs
C/N ratio 15 – 30Slow SOM
15 – 100 yrsC/N ratio 10 – 25
• Recently deposited organic material• Rapid decomposition• 10 – 20% of SOM
• Intermediate age organic material• Slow decomposition• 10 – 20% of SOM
• Very stable organic material• Extremely slow decomposition• 60 – 80% of SOM
CO 2
Dekomposisi(CO2)
Erosi
Bahan organik tanah BOT
Kehil;angan
InputsSisa tanamanAkart-akar
RabukKompos
• 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
Kalau kehilangan meningkat dan intputnya konstan, maka BOT akan menurun
Soil Organic Matter
Decomposition(CO2)
Erosion
Losses
Inputs
Crop ResiduesCrop Roots
Manure Compost
Decomposition(CO2)
Erosion
Soil Organic MatterLosses
InputsCrop Residues
Crop RootsManure Compost
Kalau Input meningkat dan Kehilangannya konstan, maka BOT akan meningkat
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
leve
l
Years of cultivation
SOM in virgin soil
Steady state SOM after years of continuous
corn cultivation
New steady state SOM
level
Management change
imposed
Corn-oats-clover rotation plus
manure application
1875 1955 2005
BOT BERSIFAT DINAMISLaju 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) Waktu (0-30 hari)
Sumber: Supriyadi, 2002
APLIKASI BAHAN ORGANIK THD KANDUNGAN P-TANAH Andisol, setelah inkubasi 30 hari
Aplikasi BO P-labil (ppm) Jerapan P (%) P-tersedia (ppm)
Kontrol 24.38 95.03 3.01Akar + tajuk T.diversifolia 40.07 88.97 6.10Tajuk T.diversifolia 31.35 89.58 5.81Akar T.diversifolia 17.94 90.44 3.80Akar + tajuk T. candida 26.91 90.37 5.10Tajuk T. candida 26.48 90.66 4.88Akar T. candida 18.57 90.91 3.54Pupuk SP-36 32.17 89.79 5.52
Sumber: Supriyadi, 2002
APLIKASI BAHAN ORGANIK THD pH dan KTK TANAH Andisol, setelah inkubasi 30 hari
Aplikasi BO pH(H2O) pH(KCl) KTK
Kontrol 5.4 4.9 33.1Tithonia 25 kg 5.5 4.7 35.1Tithonia 50 kg 5.6 4.7 36.5Tithonia 75 kg 5.7 4.6 37.4Tephrosia 25 kg 5.6 4.7 36.2Tephrosia 50 kg 5.6 4.7 37.1Tephrosia 75 kg 5.6 4.6 37.1Campuran 25 kg 5.6 4.7 35.8Campuran 50 kg 5.6 4.6 36.8Campuran 75 kg 5.7 4.6 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 BOTSumber: www.microbiologyprocedure.com/or...mus.html
0
20
40
60
80
100
0 1 2 3 4 5
Totalorganicmatter
Cellulose
Lignin
Hemicellulose
Origi
nal co
mpon
ent le
ft, gra
ms
Years
Dekomposisi seresah daun Miscanthus sinensis.
…. Diunduh 15/2/2012
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.
Dekomposisi Bahan Organik
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.
Plant-carbon Animal-carbon
Soil organic matter
Microbial cells, decayed residues
Carbon dioxide
A B C
D E
C . Respiration, animalD . Autotropic microorganisms
The carbon cycle
E . Respiration, microbial
A . PhotosynthesisB . Respiration, plant
C:N Ratios as Related to Organic Matter DecompositionIn 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 Effect30:1 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.
C/N dan Dekomposisi Bahan Organik
Decomposition of Organic Matter (Mineralization)1. percent organic matter2. organic matter composition3. cultivation (crop, tillage, burning)4. climate (moisture, temperature)5. soil pH6. 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 immobilizationAs 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 needsAdding 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).
Dekomposisi 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.
C/N ratio Bahan Organik