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

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Presentasi berjudul: "MK. DASAR ILMU TANAH BAHAN ORGANIK TANAH Oleh: Soemarno JURUSAN TANAH FPUB NOP. 2013 MK. DASAR ILMU TANAH BAHAN ORGANIK TANAH Oleh: Soemarno JURUSAN TANAH."— Transcript presentasi:

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

2 SIKLUS KARBON Tanaman Hewan CO2 Pupuk Kandang Reaksi dalam Tanah CO2 Aktivitas Mikroba Kehilangan drainage CO2, senyawa karbonat dari K, Ca, Mg, dll.

3 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.

4 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

5 BAHAN ORGANIK TANAH KANDUNGAN, JENIS-JENIS, KARAKTERISTIKNYA

6 BAHAN ORGANIK TANAH BENTUK-BENTUK KARBON DALAM TANAH

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

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

9 BAHAN ORGANIK TANAH BO)T mencakup semua komponen organik dari tanah: 1.Residu segar 2.BO yang sedang mengalami dekomposisi 3.BO yang stabil 4.Organisme hidup

10 RESIDU SEGAR 1.Hingga 15% dari BO berupa residu segar (biasanya <10) 2.Terdiri atas guguran dedaunan 3.Dapat dikenali beragam tipe seresah tumbuhan

11 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.

12 PERUBAHAN BAHAN ORGANIK YG DITAMBAHKAN KE TANAH I. Senyawa dalam jaringan tumbuhan segar Sukar DilapukMudah dilapuk LigninSelulose MinyakZat pati LemakGula Resin,dllProtein,dll II. Hasil intermedier dekomposisi Senyawa tahan lapuk Senyawa tidak tahan lapuk ResinAsam amino LilinAmida Minyak dan lemakAlkohol Lignin,dllAldehide, dll III. Hasil pelapukan dan tahan lapuk Hasil akhir yg sederhana Humus: kompleks koloidalCO2 dan air dari ligno-proteinNitrat Sulfat Fosfat, Senyawa Ca,dll.

13 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.

14 Parameter BIOMASA Tithonia diversifolia Tephrosia candida Kadar air, % N-total, % P-total, % C-total, % C/N C/P Lignin, % Polifenol, % K, % Ca, % Mg, % Asam-asam organik, g/kg: Sitrat3286 Oksalat1130 Suksinat480 Asetat1716 Malat77515 Butirat490 Propionat310 Phtalat2019 Benzoat6956 Salisilat012 Galat00 Sumber: Supriyadi, 2002.

15 APLIKASI BAHAN ORGANIK THD KANDUNGAN ASAM ORGANIK DLM TANAH, setelah 30 hari Aplikasi BOKonsentrasi asam dlm tanah Andisol (ppm): Sitrat Oksalat Suksinat Asetat Malat Butirat Total T. candida T. diversifolia Campuran Sumber: Supriyadi, 2002

16 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

17 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

18 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

19 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

20 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

21 SIFAT & CIRI BOT Voids can trap –Water –Minerals –Other organic molecules Hydrophobicity/hydrophilicity Reactivity H-bonding, chelation of metals

22 Fig 3.8

23 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?

24 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

25 CO 2 Detritus (Plant Debris) FungiEarthworms Bacteria Soil Humus Organic Matter Biomass Humin (insoluble) Humic Acid (insoluble in acid) Fulvic Acid (soluble) degradation (nonliving, nontissue decay products) (identifiable dead tissue) (living organisms)

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

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

28 Gugus fungsional reaktif: karboksil, hidroksil, fenolik HUMUS 1. Kapasitas pertukaran kation (anion) sangat besar 2.Kapasitas penyimpanan air sangat besar 3. Membantu agregasi tanah

29 BAHAN ORGANIK TANAH CARA MENGUKURNYA

30 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

31 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: …… 26/10/2012

32 ANALISIS BAHAN ORHANIK TANAH Diunduh dari sumber: …… 26/10/2012 Soil Analysis - Organic Matter Walkley- Black Method 1.Jackson, M. L Soil Chemical Analysis Walkley, A 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: Walkley, A. and I. A. Black An Examination of Degtjareff Method for Determining Soil Organic Matter and a Proposed Modification of the Chromic Acid Titration Method. Soil Sci. 37: Schollenberger, C. J A Rapid Approximate Method for Determining Soil Organic Matter. Soil Sci. 24:65-68.

33 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

34 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, Sand

35 Steps in the cycling of soil C and the formation of soil organic matter and humus. Diunduh dari sumber: …… 27/10/2012

36 General flow of the sequential SOM fractionation procedure. Diunduh dari sumber: /pii/S …… 27/10/2012

37 BAHAN ORGANIK TANAH FUNGSINYA

38 Komponen-komponen dari Sistem Manajemen Tanah-Berkelanjutan Sumber:

39 Hubungan antara Pembangunan Berkelanjutan dengan Manajemen Tanah Berkelanjutan (Redrawn from Dumanski 1997) Sumber:

40

41 Fungsi & Peranan Bahan Organik Tanah (Soil Organic Matter) Fungsi BOT

42 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

43 BOT menjaga Sifat Olah Tanah Membantu infiltrasi air hujan dan udara ke dalam tanah Membantu menahan air Mengurangi erosi tanah

44 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.

45 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

46 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 Poor Good

47 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.

48 Kontribusi Biota Tanah pada Dekomposisi BOT Sumber:

49 Perubahan Kandungan Bahan Organik Tanah (jangka panjang) pada berbagai kondisi pengelolaan tanah Sumber:

50 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:

51 BAHAN ORGANIK TANAH: FAKTOR YANG MEMPEMNGARUHI BOT

52 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?

53 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

54 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

55 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

56 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

57 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

58 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

59 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? Untuk mempertahankan hasil tanaman, diperlukan penambahan Hara N dari pupuk, rabuk kandang dan Tanaman legume manures or legumes are required

60 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 = lbs lbs * 2%N in the grain = 2400 lbs N/acre over 100 years 8000 lbs N in the soil (1892) lbs N in the soil (1992) lbs N removed in the grain lbs N (10 lb N/ac/yr added via rainfall in 100 years) =4600 lbs N unaccounted KEHILANGAN BOT

61 N removal in the Check (no fertilization) plot of the Magruder Plots 20 bu/acre * 60 lb/bu * 100 years = lbs lbs * 2%N in the grain = 2400 lbs N/acre over 100 years 8000 lbs N in the soil (1892) lbs N in the soil (1992) lbs N removed in the grain lbs N (10 lb N/ac/yr added via rainfall in 100 years) = 4600 lbs N unaccounted Plant N Loss Denitrification KEHILANGAN BOT

62 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

63

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

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

66 BAHAN ORGANIK TANAH: DEKOMPOSISINYA

67 Daur-Ulang Unsur Hara. Diunduh dari sumber: 26/10/2012 FungiBakteri

68 Most of the N is in the soil organic matter. Diagram of N Cycle Sumber:

69 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: …… 26/10/2012

70 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: …… 26/10/2012

71 PROSES DEKOMPOSISI BAHAN ORGANIK Diunduh dari sumber: 26/10/2012 Mekanisme pembentukan substansi humik dlaam tanah.

72 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) 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 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

73 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 + NH 4 + NO 3 -

74 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 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 dlmTingkatan humus jaringan aslitanah Senyawa jasad Humus tanah BO segar waktu HUMUS

75 ENERGI BAHAN ORGANIK TANAH Bahan organik berfungsi sebagai Sumber karbon dan sumber energi bagi jasad renik tanah Bahan organik tumbuhan mengandung energi 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 juta kcal energi potensial setiap hektar lapisan olah, ini setara dengan ton batu bara Bahan organik berfungsi sebagai Sumber karbon dan sumber energi bagi jasad renik tanah Bahan organik tumbuhan mengandung energi 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 juta kcal energi potensial setiap hektar lapisan olah, ini setara dengan 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. 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.

76 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

77 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

78 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

79 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

80 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

81 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 nematode Rotifer DEKOMPOSISI BAHAN ORGANIK

82 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 (CO 2 ) Bacteria, Fungi Soil organic matter Bacteria, Fungi Soil organic matter Nematodes, protists, humus CO 2 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

83 Average C/N ratio of bacteria and fungi is 8:1 Litter C/N ratio around 24:1 CO 2 C/N ratio 8:1 2/3 of carbon released as CO 2 Microbial C/N ratio is maintained at 8:1 with no uptake or release of N Dekomposisi Bahan Organik: C/N ratio

84 2/3 of carbon released as CO 2 Average C/N ratio of bacteria and fungi is 8:1 Litter C/N ratio around 90:1 CO 2 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

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

86 Bahan organik dalam tanah tidak homogen Scientists describe 3 pools of soil organic matter Passive SOM 500 – 5000 yrs C/N ratio 7 – 10 Active SOM 1 – 2 yrs C/N ratio 15 – 30 Slow SOM 15 – 100 yrs C/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

87 Dekomposisi (CO 2 ) Erosi Bahan organik tanah BOT Kehil;angan Inputs Sisa tanaman Akart-akar Rabuk Kompos 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

88 Kalau kehilangan meningkat dan intputnya konstan, maka BOT akan menurun Soil Organic Matter Decomposition (CO 2 ) Erosion Losses Inputs Crop Residues Crop Roots Manure Compost

89 Decomposition (CO 2 ) Erosion Soil Organic Matter Losses Inputs Crop Residues Crop Roots Manure Compost Kalau Input meningkat dan Kehilangannya konstan, maka BOT akan meningkat

90 BOT tidak akan secara kontinyu meningkat atau menurun When inputs or losses are changed, SOM quantity changes to a different level and a new steady state condition is reached. SOM level 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

91 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”

92 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.. 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++, ……. 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++, …….

93 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

94 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

95 APLIKASI BAHAN ORGANIK THD KANDUNGAN P-TANAH Andisol, setelah inkubasi 30 hari Aplikasi BOP-labil (ppm) Jerapan P (%) P-tersedia (ppm) Kontrol Akar + tajuk T.diversifolia Tajuk T.diversifolia Akar T.diversifolia Akar + tajuk T. candida Tajuk T. candida Akar T. candida Pupuk SP Sumber: Supriyadi, 2002

96 APLIKASI BAHAN ORGANIK THD pH dan KTK TANAH Andisol, setelah inkubasi 30 hari Aplikasi BO pH(H2O)pH(KCl)KTK Kontrol Tithonia 25 kg Tithonia 50 kg Tithonia 75 kg Tephrosia 25 kg Tephrosia 50 kg Tephrosia 75 kg Campuran 25 kg Campuran 50 kg Campuran 75 kg Sumber: Supriyadi, 2002

97 Adequate levels of SOM can be maintained with: –proper fertilization, –crop rotations, and tillage practices –Returning crop residues to the soil.

98 Degradasi Residu Tanaman dan Pembentukan BOT Sumber:

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

100 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

101 The carbon cycle revolves around CO 2, its fixation and regeneration. Chlorophyll-containing plants utilize CO 2 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, CO 2 concentrations in the atmosphere would decrease and photosynthesis rates would decrease.

102 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 RatioEffect 30:1immobilization <20:1mineralization 20-30:1immobilization = 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

103 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 CO 2 (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). Dekomposisi Bahan Organik

104 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 CO 2 evolution and NO 3 is initially immobilized. 6.Within one yearly cycle in a temperate climate, net increase in NO 3 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 CO 2 is being evolved via the microbial decomposition of organic matter. C/N ratio Bahan Organik


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