BAHAN ORGANIK TANAH MK. DASAR ILMU TANAH Oleh: Soemarno JURUSAN TANAH FPUB NOP. 2013

Kehilangan drainage CO2, senyawa karbonat dari K, Ca, Mg, dll. 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 Before giving this program, add your name and county to the “Prepared by” list in the space below “Department of Crop and Soil Sciences” There are some slide builds included in this program. These are indicated with a bold face “Click” in the text. Managing the soils on your farm so that they can continue to produce high quality crops year after year requires balancing many different operations and inputs to maintain soil quality. Today we are going to talk about one important aspect of soil quality, namely soil organic matter content, and consider how management affects soil organic matter.

BENTUK-BENTUK KARBON DALAM TANAH BAHAN ORGANIK TANAH

SUSUNAN JARINGAN TUMBUHAN Air 75% Padatan 25% Karbon 11% Oksigen 10% Hidrogen 22% Abu 2%

SUSUNAN BAHAN TUMBUHAN YG DITAMBAHKAN KE TANAH AIR 75% Padatan 25%. Gula & Pati (1-5% ) Hemiselulose 10-30% Selulose 20-50% SUSUNAN UNSUR Hidrat Arang 60% Protein 10% Lignin 20-30% Karbon 44% Hidrogen 8% Abu Oksigen 40% Lemak, lilin, tanin 1-8%.

BO)T mencakup semua komponen organik dari tanah: BAHAN ORGANIK TANAH BO)T mencakup semua komponen organik dari tanah: Residu segar BO yang sedang mengalami dekomposisi BO yang stabil Organisme hidup

RESIDU SEGAR Hingga 15% dari BO berupa residu segar (biasanya <10) Terdiri atas guguran dedaunan Dapat dikenali beragam tipe seresah tumbuhan

BO yang sedang mengalami Dekomposisi Biomasa tanaman ditransformasikan dari satu senyawa organik menjadi senyawa organik lainnya oleh organisme tanah Organisme menghasilkan bahan-sisa, hasil samping dan sel-sel tubuhnya 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 Selulose Minyak Zat pati Lemak Gula Resin,dll Protein,dll II. Hasil intermedier dekomposisi Senyawa tahan lapuk Senyawa tidak tahan lapuk Resin Asam amino Lilin Amida Minyak dan lemak Alkohol Lignin,dll Aldehide, dll III. Hasil pelapukan dan tahan lapuk Hasil akhir yg sederhana Humus: kompleks koloidal CO2 dan air dari ligno-protein 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 Tithonia diversifolia Tephrosia candida Kadar air, % 70.2 62.1 N-total, % 2.1 1.7 P-total, % 0.3 0.1 C-total, % 38.5 33.9 C/N 19 21.1 C/P 128 305 Lignin, % 9.8 12.1 Polifenol, % 3.3 5.1 K, % 2.1 1.7 Ca, % 1.3 1.2 Mg, % 0.6 0.2 Asam-asam organik, g/kg: Sitrat 32 86 Oksalat 11 30 Suksinat 48 0 Asetat 17 16 Malat 775 15 Butirat 49 0 Propionat 31 0 Phtalat 20 19 Benzoat 69 56 Salisilat 0 12 Galat 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

Citizen Science – Kansas State 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 it can decline rapidly if the soil environment changes and renewable 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 Hydrophobicity/hydrophilicity 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?

Sumber: ag.arizona.edu/pubs/garden/mg/so...ils.html 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...ils.html

Detritus (Plant Debris) Organic Matter Biomass (living organisms) CO2 Detritus (Plant Debris) (identifiable dead tissue) degradation Fungi Earthworms Bacteria Soil Humus (nonliving, nontissue decay products) Humin (insoluble) Humic Acid (insoluble in acid) Fulvic Acid (soluble)

CADANGAN BOT BOT Aktif BOT Stabil KTK Mikro-agregasi BOT Total Menekan Penyakit Agregasi tanah Suplai hara BOT Aktif Dekomposisi BOT Stabil KTK Mikro-agregasi BOT Total

DEGRADASI BOT: SIKLUS HARA Biomasa Biomass Detritur (seresah Tumbuhan) Detritus (Plant Debris) Nutrient Incorporation Penyerapan Hara Pelepasan Hara Nutrient Release Humus Tanah Soil Humus

Gugus fungsional reaktif: karboksil, hidroksil, fenolik HUMUS Gugus fungsional reaktif: karboksil, hidroksil, fenolik Kapasitas pertukaran kation (anion) sangat besar Kapasitas penyimpanan air sangat besar 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 Soil Analysis - Organic Matter Walkley-Black Method 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. 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/

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 & 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 Poor Good 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 Poor Good http://www.nrsl.umd.edu/research/NRSLResearchAreaInfo.cfm?ID=14

KESEHATAN TANAH Cornell researcher George Abawi describes soil health strategies at an Onion Council field day in Wayne County, N.Y.Photo by Carol R. MacNeil. 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 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

Sumber: www.agnet.org/library/eb/473/ Perubahan Kandungan Bahan Organik Tanah (jangka panjang) pada berbagai kondisi pengelolaan tanah Sumber: www.agnet.org/library/eb/473/

Sumber: www.climatescience.gov/Library/s...hap7.htm 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

FAKTOR YANG MEMPEMNGARUHI BAHAN ORGANIK TANAH: FAKTOR YANG MEMPEMNGARUHI BOT

Faktor yang mempengaruhi BOT Morrow Plots – Why the difference in SOM? 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. 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 ADDED 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 Leaf 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 No-till management practices (10 yrs no-tillage with corn, OC in surface 30 cm increased by 0.25% (Blevins et al. 1983). 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, 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). For thousands of years, organic matter levels were allowed to increase in these native prairie soils since no cultivation was ever employed. 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).

Should the decline in years 1-5 be greater? Untuk mempertahankan hasil tanaman, diperlukan penambahan Hara N dari pupuk, rabuk kandang dan Tanaman legume manures or legumes are required 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 Plant N Loss Denitrification 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 ___________________________ __________ 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 +

Kultivasi & Penambahan Jerami, Immobilisasi N & mineralisasi N, Pelepasan CO2

Perubahan Kadar N Jerami yang sedang mengalami dekomposisi (From Alexander, 1977).

Perubahan kandungan N-tanah merupakan fungsi waktu, penambahan rabuk dan jerami

BAHAN ORGANIK TANAH: DEKOMPOSISINYA Before giving this program, add your name and county to the “Prepared by” list in the space below “Department of Crop and Soil Sciences” There are some slide builds included in this program. These are indicated with a bold face “Click” in the text. Managing the soils on your farm so that they can continue to produce high quality crops year after year requires balancing many different operations and inputs to maintain soil quality. Today we are going to talk about one important aspect of soil quality, namely soil organic matter content, and consider how management affects soil organic matter.

Daur-Ulang Unsur Hara. Bakteri Fungi Diunduh dari sumber: 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 (cepat dilapuk) 2. Protein kasar 3. Hemiselulose 4. Selulose 5. Lignin,lemak, lilin, dll. (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 HUMUS Protein 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 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 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 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

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 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. Fungus on poplar leaf Tree trunk rotted by fungi Fairy ring Soil fungus

Fungi dan Struktur Tanah Hifa Fungi (benang) membantu memegang granula tanah Eksudat 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

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 Amoeba Bacteria-feeding nematode Rotifer 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) 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 Plant litter 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 2/3 of carbon released as CO2 Average C/N ratio of bacteria and fungi is 8:1 Microbial C/N ratio is maintained at 8:1 with no uptake or release of N

Dekomposisi Bahan Organik: C/N ratio CO2 Litter C/N ratio around 90:1 2/3 of carbon released as CO2 C/N ratio 30:1 Average C/N ratio of bacteria and fungi is 8:1 Microbial C/N ratio is maintained at 8:1 by taking up N from soil Immobilisasi Soil N

2/3 carbon dibebaskan sebagai CO2 Dekomposisi BO dan C/N-ratio CO2 C/N ratio seresah tanaman sekitar 9:1 2/3 carbon dibebaskan sebagai CO2 C/N ratio 3:1 Rataan C/N ratio bakteri dan fungi 8:1 Microbial C/N ratio is maintained at 8:1 by releasing N to the soil Mineralisasi N-tanah

Bahan organik dalam tanah tidak homogen Scientists describe 3 pools of soil organic matter Organic Material CO2 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 Intermediate age organic material Slow decomposition 10 – 20% of SOM Passive SOM 500 – 5000 yrs C/N ratio 7 – 10 Very stable organic material Extremely slow decomposition 60 – 80% of SOM

Erosi Sisa tanaman Akart-akar Rabuk Inputs Kompos Dekomposisi (CO2) 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 Decomposition (CO2) Crop Residues Crop Roots Manure Compost Inputs Soil Organic Matter Losses Erosion

Kalau Input meningkat dan Kehilangannya konstan, maka BOT akan meningkat Crop Residues Crop Roots Manure Compost Inputs Soil Organic Matter Decomposition (CO2) 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 in virgin soil Corn-oats-clover rotation plus manure application Management change imposed SOM level Steady state SOM after years of continuous corn cultivation New steady state SOM level 1875 1955 2005 Years of cultivation

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 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. 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 3.01 Akar + tajuk T.diversifolia 40.07 88.97 6.10 Tajuk T.diversifolia 31.35 89.58 5.81 Akar T.diversifolia 17.94 90.44 3.80 Akar + tajuk T. candida 26.91 90.37 5.10 Tajuk T. candida 26.48 90.66 4.88 Akar T. candida 18.57 90.91 3.54 Pupuk 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 33.1 Tithonia 25 kg 5.5 4.7 35.1 Tithonia 50 kg 5.6 4.7 36.5 Tithonia 75 kg 5.7 4.6 37.4 Tephrosia 25 kg 5.6 4.7 36.2 Tephrosia 50 kg 5.6 4.7 37.1 Tephrosia 75 kg 5.6 4.6 37.1 Campuran 25 kg 5.6 4.7 35.8 Campuran 50 kg 5.6 4.6 36.8 Campuran 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 BOT Sumber: www.microbiologyprocedure.com/or...mus.html

Dekomposisi seresah daun Miscanthus sinensis. …. Diunduh 15/2/2012

Dekomposisi Bahan Organik As decomposition proceeds, water soluble fractions (sugars, starch, organic acids, pectins and tannins and array of nitrogen compounds) readily utilized by microflora. Ether and alcohol-soluble fractions (fats, waxes, resins, oils), hemicelluloses and cellulose decrease with time as they are utilized as carbon and energy sources. Lignin, persists and can accumulate in the decaying biomass because of its resistance to microbial decomposition. 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. 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.

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 C:N ratios say nothing about the availability of carbon or nitrogen to microorganisms Why? What makes up the carbon (C) component In tropical soils, significantly higher proportions of lignin will be present in the organic matter 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. Therefore, mineralization rates in organic matter that contain high proportions of lignin will be much smaller C:N ratios discussed were generally developed from data obtained in temperate climates. 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 1000+yrs prior to the time cultivation was initiated, C and N had built up in native prairie soils. C:N ratio was wide, reflecting conditions for immobilization of N. Combined influence of tillage and the application of additional organic materials (easily decomposable wheat straw and/or corn stalks) Cultivation alone unleashed a radical decomposition of the 4% organic matter in Oklahoma soils. Easily decomposable organic materials added back to a cultivated soil, increases CO2 evolution and NO3 is initially immobilized. 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. Percent N in added organic material increases while the C:N ratio decreases 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.