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