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bahan kajian MK. DASAR ILMU TANAH UDARA TANAH DAN AERASI Oleh : Prof Dr.IR.Soemarno,M.S . Jurusan Tanah FP UB Nop 20

bahankajianMK. DASAR ILMU TANAHUDARA TANAH DAN AERASIOleh:Prof Dr.IR.Soemarno,M.S.Jurusan Tanah FP UB Nop 2011Tanah yang AERASI nya baik adalah tanah yg mengandung gas…
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bahankajianMK. DASAR ILMU TANAHUDARA TANAH DAN AERASIOleh:Prof Dr.IR.Soemarno,M.S.Jurusan Tanah FP UB Nop 2011Tanah yang AERASI nya baik adalah tanah yg mengandung gas tersedia dalam jumlah dan perbandingan yang tepat bagi jasad aerobik yang hidup dan mampu menunjang berlangsungnya proses metabolik yg esensial bagi jasad tsb pd kecepatan yg optimumTanah yang AERASI nya baik mempunyai sifat:1. Harus ada ruangan yang cukup tanpa bahan mineral dan air2. Harus ada kesempatan yg cukup bagi gas-gas untuk keluar-masuk ruangan tsbAERASI TANAHDua reaksi biologis yg terkait dgn dinamika O2 dan CO2 dalam tanah:1. Pernafasan akar tumbuhan tinggi 2. Dekomposisi bahan organik tanah secara aerobik oleh jasad renik. (C) + O2 CO2Penyebab buruknya aerasi tanah:1. Kandungan air tanah yg berlebihan shg tidak menyisakan ruangan untuk gas/ udara2. Pertukaran gas tidak cukup cepat unt mempertahankan kadarnya pd tingkat tertentu.Air Tanah yang berlebihan1. Tanah jenuh air, tanah tergenang dapat berpengaruh buruk pd tanaman pd umumnya2. Biasanya pd tanah-tanah yg drainasenya buruk dan tekstur halus3. Pada tempat-tempat cekunganMASALAH AERASI TANAHPERTUKARAN GAS antara tanah dan atmosfer tgt pd:1. Laju reaksi biokimia yg mempengaruhi gas dlm tanah 2. Laju ke luar - masuknya gas-gas dari dan ke dalam tanah.Pertukaran gas ini terjadi melalui mekanisme: 1. Pergerakan masal (mass flow) 2. Difusi gasLDO adalah laju pergantian oksigen dalam tanah yg dipakai oleh akar tanaman yg bernafas atau digantikan oleh air. Nilai LDO semkin kecil dengan kedalaman tanah LDO pada kedalaman 95 cm sama dengan setengah nilai LDO pd kedalaman 11.5 cmLAJU DIFUSI OKSIGEN (LDO)Pertumbuhan akar tanaman berhenti bila LDO turun menjadi 20 g x 10-8 cm2/menit Udara tanah umumnya lebih kaya CO2 dan uap air , gas metan dan H2S dibandingkan dengan udara atmosfer.Sejumlah gas-gas tertentu dapat larut dalam air tanah dan diikat oleh permukaan koloid tanah, misalnya oksigen % volume:Tempat O2 CO2 N2Udara tanah: New York 15.10 4.50 81.40 Inggris 20.65 0.25 79.20Udara Atmosfer Inggris 20.97 79.00Sumber: Lyon, Buckman & Brady, 1952.SUSUNAN UDARA TANAH Susunan udara tanah tgt pada: 1. Jumlah ruangan / pori yg tersedia 2. Kecepatan reaksi biokimia 3. Pertukaran gasPenambahan bahan organik akan mengubah susunan udara tanahTanah lapisan atas vs Tanah lapisan bawahJumlah total ruangan pori tanah lapisan bawah lebih sedikit dibanding tanah lapisan atas % CO2 udara tanah Kedalaman sampling, cm0.5 gandum + rabuk 30 tanah bera + rabuk kandang Lempung liat berdebu Lempung berdebu tanah bera 180 Waktu sampling 10 20 % O2 udra tnhFaktor Susunan Udara Tanah Jasad Mikro1. Aerasi buruk menurunkan oksidasi bahan organik tanah2. Penurunan ini lebih disebabkan oleh kekurangan O23. Populasi jasad renik sangat terpengaruhi olh aerasi4. Aerasi buruk mendorong aktifitas jasad anaerob dan fakultatif, menghasilkan senyawa reduksi, fero, mangano, sulfidaAerasi b uruk mempengaruhi Tanaman:1. Pertumbuhan perakaran sangat terbatas2. Penyerapan hara terhambat3. Air menjadi berkurang4. Pembentukan senyawa anorganik yang bersifat toksikAERASI &KEGIATAN BIOLOGISAkar tanaman apel memerlukan minimal 3% O2 dalam udara tanah , sedangkan 5 - 10% cukup untuk pertumbuhan akar. Minimal diperlukan udara tanah yg mengandung 12% O2 untuk pertumbuhan akar-akar baru.Pertumbuhan tajuk tanaman normal selama LDO lebih dari 30-40 g x 10-8 /cm2/menit.Dekomposisi anaerobik C6H12O6 3CO2 + 3 CH4 gula metanTanaman Tekstur LDO pada kedalaman: Kondisi 10 cm 20 cm 30 cm pertumbuhan tanamanBrokoli Lempung 53 31 38 Sangat baikSelada Lempung berdebu 49 26 32 BaikPhaseolus sp Lempung 27 27 25 Klorosis Arbei Lempung berpasir 36 32 34 KlorosisKapas Lemping berliat 7 9 - KlorosisJeruk Lempung berpasir 64 45 39 Pertumbuhan akar cepatSumber: Stolzy dan Letey, 1964.AERASI &EFEK LAIN Kondisi aerasi tanah berpengaruh terhadap bentuk unsur hara penting:Unsur Kondisi Oksidasi Kondisi reduksi (tergenang)Karbon CO2 CH4Nitrogen NO3- N2, NH4+Belerang SO4= H2S, S=Tindakan untuk memperbaiki aerasi ntanah:1. Menghilangkan air yang berlebihan (drainase)2. Memperbaiki agregasi dan pengolahan tanahAdaptasi Tanaman-Tanah :1. Pohon buah-buahan dan tanaman berakar dalam memerlukan solum tanah yang dalam (tebal), aerasinya baik, dan sangat peka terhadap kekurangan oksigen dalam tanah2. Pengelolaan tanaman ditentukan oleh baik-buruknya aerasi tanahAERASI &KEGIATAN PengelolaanSuhu tanah sangat vital bagi aktivitas biologis dalam tanah, termasuk pertumbuhan akar tanaman.Proses nitrifikasi baru dapat berlangsung kalau suhu tanah telah mencapai 5oC, batas optimumnya 27 - 33oCSuhu tanah di lapangan ditentukan oleh:1. Jumlah panas yang diserap oleh tanah2. Energi panas yg diperlukan untuk mengubah suhu tanah3. Energi yg diperlukan untuk evaporasi yg terus menerus di permukaan tanahSUHU TANAHAmplitude of seasonal soil temperature change as a function of depth below ground surface.Sumber: http://www.geo4va.vt.edu/A1/A1.htm Jumlah panas yg diserap tanah ditentukan oleh radiasi efektif yg mencapai permukaan tanah dan iklimJumlah energi yg masuk tanah dipengaruhi oleh: 1. Warna tanah: gelap menyerap lebih banyak energi 2. Lereng: 3. Tanaman penutup tanah: Hutan vs. tanah gundulTanah gundul lebih cepat memanas dan mendinginKehilangan panas dari tanah ke atmosfer, melalui KONDUKSI dan RADIASIRadiasi ini berupa infra merah, tidak terlihat mata, gelombang gelapRadiasi gelombang gelap ini berenergi tinggi dan selama pemancarannya banyak panas yg hilang dari tanahThermal Admittance (λ/Cv) 1/2 : Represents ability of soil to accept and release heat.  Soils with low thermal admittance have extreme surface temperature fluctuations. Because water has a HIGH heat capacity and is a GOOD conductor, wet soils will have a HIGH thermal admittance..SERAPAN & KEHILANGAN PANASThermal AdmittanceSource: Lesley DampierPanas jenis tanah: Jumlah panas yang diperlukan oleh satu gram tanah untuk menaikkan suhunya satu derajat celcius.Panas jenis tanah kering lebih rendah dibandingkan dg tanah basahTanah kering : PJ = 0.20Kadar air 20% : PJ = 0.33Kadar air 30% : PJ = 0.38Thermal Conductivity (λ): Measure of the ease with which a soil transmits heat.It describes heat flow in response to a temperature gradient..PANAS JENIS TANAH Thermal ConductivitySource: Lesley DampierPenguapan air tanah memerlukan sejumlah energi panasUntuk menguapkan 1 g air pada 20oC diperlukan panas 585 kalori. Penguapan 0.452 g air memerlukan 265 kalori. Bila semua panas ini diambil dari tanah dan air, maka tanah sedalam 30 cm menjadi dingin dan suhunya sama dengan -2oC.Warna tanah vs. SuhuTanah gelap biasanya kaya bahan organik dan kandungan airnya tinggi.Tanah gelap yg drainasenya buruk lambat memanas.Soil Heat Capacity (Cv): Amount of heat needed to cause a 1oC change in temperature of a unit volume of soil.PANAS PENGUAPAN Soils with high Cv are buffered against temperature change .It is much easier to raise soil temperature by 1oC in a dry soil than wet soil Heat CapacitySource: Lesley DampierEnergi panas masuk ke dalam tanah melalui proses konduksi, sehingga kadar air tanah sangat menentukan laju konduksi ini.Energi panas lebih mudah menjalar dari tanah ke air dibandingkan dari tanah ke udaraProses konduksi panas dalam tanah berlangsung lambat. Tanah lapisan bawah suhunya lebih rendah dp tanah lapisan atas. Perubahan suhu tanah lapisan bawah sangat sedikit sekaliThermal Diffusivity (λ/C): An indication of subsurface temperature response to surface temperature change.. Soils with high thermal diffusivity undergo large and rapid subsurface temperature responses to surface temperature change.. Does not change much with water content in organic soil, but in mineral soils, the peak thermal diffusivity occurs near field capacityGERAKAN PANAS DALAM TANAH Heat CapacitySource: Lesley DampierSuha tanah pada suatu saat tergantung pada nisbah energi panas yang diserap dan yang hilangSuhu tanah juga tergantung kedalaman tanah Suhu tanah. oC 15 20 25 30 35Soildepthcm 60 Januari Juli 300 Sumber: Fluker, 1956 (Texas)SUHU TANAHPenggunaan mulsa organik mengakibatkan suhu tanah lebih rendah dan lebih merataPengelolaan air tanah secara tepat juga akan mempengaruhi suhu tanahSuhuoC Kedalaman tanah 1.5 cm Kedalaman tanah 15 cm 38tanpa mulsa Dengan mulsaTanpa mulsaDengan mulsa pagi sore pagi sorePengendalian Suhu TanahAERASI TANAH : Kemampuan tanah untuk melakukan pertukaran gas dengan atmosfer. Proses aerasi tanah ini melibatkan laju ventilasi,Komposisi udara tanah, proporsi pori tanah yang terisi dengan udara, dan potensial reaksi redoksMicropores (d<0.08mm) occur within aggregates.  They are usually filled with water and are too small to allow much movement of air.  Water movement in micropores is extremely slow and much of the water held by them is unavailable to plants. Sumber: http://www.landfood.ubc.ca/soil200/interaction/water_air.htm  ‘Goose’ Your Lawn for Good Soil Health  By Shayne Hale June 2, 2011Aeration is essential and fairly simple to do. Most rental centers have a lawn aerator that they will rent out by the day or perhaps by the hour. This machine is simply a large drum with spikes or tubes around the drum. Usually gas powered, this machine removes “plugs” of soil, thereby allowing the soil to breathe, and decreases soil compaction, which increases microbial action in the soil. Also, lawn aerating promotes deeper root growth and, in time, a healthier lawn with fewer weeds. A healthy, robust lawn should choke out intruders.Sumber: http://anewscafe.com/2011/06/02/goose-your-lawn-for-good-soil-health/Lawn Aeration for a Greener, Thicker, Healthier Lawn!More Benefits of Lawn AerationAeration loosens compacted soil and breaks up thatch. It allows water and other nutrients to seep into the soil, encouraging new root growth and establishing a stronger, deeper root base for a lusher, healthier turf. Another benefit of aeration is the reduction of water runoff and puddling. Lawn Aeration permits the root system to go deeper where the ground temperature is cooler and moister, allowing the grass to stay greener longer in the heat of the summer. Remember, 90% of grass is in the roots!A healthy root system is a must for an attractive lawn. Oxygen in the soil is vital for healthy roots. Root growth is inhibited by clay and compacted soils because of a restricted oxygen supply. Aerating improves rooting and problem soils by allowing air into the soil. Umber: http://yardplug.com/FAQ/FAQ1.htmSumber: organicsoilsolutions.comPemadatan tanah berarti tanah menjadi lebih padat, porositasnya berkurang, sehingga jumlah dan pergerakan udara dalam tanah juga terbatas. Hal ini dapat mengganggu pertumbuhan akar tanamanMechanism of Gas Exchange in Soils:Mencegah defisiensi O2 atau toksisitas CO2Mekanisme pergerakan gasMass FlowMovement of a mass of air (gases move togetherDriven by gradients in total pressure differences  Caused by changes in temperature (ideal gas law)Caused by movement of water downward  Diurnal flow of air in upper few inches (soil breath?)DiffusionEach gas moves down gradients of its own concentration   Even with no overall pressure difference  O2 and CO2 diffusing past each other in opposite directionsSumber; http://faculty.plattsburgh.edu/robert.fuller/370%20Files/Weeks13Soil%20Air%20&%20Temp/aastart14.htmFunction of concentration gradient and resistanceResistance: Increases with reductions in pore sizeO2 gradient: Decreases with depth due to O2 consumptionGradient decreases with depth;   less ODR.O2 Diffusion rate (ODR) :  Rate of movement across a cross-sectional area ;   ug O2/cm2.minuteSumber; http://faculty.plattsburgh.edu/robert.fuller/370%20Files/Weeks13Soil%20Air%20&%20Temp/aastart14.htmFaktor-faktor yang mempengaruhi AerasiExcess Moisture    -   diffusion of water very slow through water Soil texture    -  heavy soils    -   reduced pore size, greater resistance   Poor Structure   -  macropores increase ODR   Position on Slope    -   excess moisture at bottom Impermeable Layers   Soil Depth  -    subsoils farther away from surface  (less ODR) Rate of O2 consumption (high labile OM content)Sumber; http://faculty.plattsburgh.edu/robert.fuller/370%20Files/Weeks13Soil%20Air%20&%20Temp/aastart14.htmPOTENSIAL REDOKS (Eh)Measured with a platinum (redox) electrode attached to a pH meter. Ranges from -400 millivolts (reducing) to +600 mV (oxidizing conditions) Measure of the relative concentration of reduced vs. oxidized forms Reduced forms have available electrons, carried by H, or less positive charge;   Oxidized forms have more O, or higher positive charge   Sensitive roots are adversely affected below +300 mV   Other plants are tolerant (adaptations, such as aerenchyma)   As O2 availability declines:  step down through bacteriological reactions using alternate oxidants.Sumber; http://faculty.plattsburgh.edu/robert.fuller/370%20Files/Weeks13Soil%20Air%20&%20Temp/aastart14.htmStructure of soil, indicating presence of bacteria, inorganic, and organic matter, water, and air. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com).Posisi dan lokasi udara dalam pori, di dalam struktur tanahMacropores (d>0.08mm) occur between aggregates (interped pores) or individual grains in coarse textured soil (packing pores) and may be formed by soil organisms (biopores).  They allow ready movement of air and the drainage of water and provide space for roots and organisms to inhabit the soil. SUMBER: http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookPLANTHORM.htmlTEKSTUR TANAH: THE KEY TO MANAGEMENT OF SOIL – PLANT – WATER RELATIONSHIPSoil is the voluminous upper part of the earth crust that consists of unconsolidated inorganic particles and organic fragments with pore spaces between and within them. Pore spaces contain soil air, and soil solution. In other words, soil volume consists of solid, liquid and gaseous phases..SUMBER: http://www.ecoconsulting.com/balance.htmPerbandingan antara komposisi udara tanah dan atmosfirSumber: http://www.ctahr.hawaii.edu/mauisoil/a_comp04.aspxKandungan O2 dan CO2 pada berbagai kedalaman tanah (Trinidad)Sumber: http://www.ctahr.hawaii.edu/mauisoil/a_comp04.aspxUDARA TANAHAir can fill soil pores as water drains or is removed from a soil pore by evaporation or root absorption. The network of pores within the soil aerates, or ventilates, the soil. This aeration network becomes blocked when water enters soil pores. Not only are both soil air and soil water very dynamic parts of soil, but both are often inversely related:An increase in soil water content often causes a reduction in soil aeration.Likewise, reducing soil water content may mean an increase in soil aeration.Since plant roots require water and oxygen (from the air in pore spaces), maintaining the balance between root and aeration and soil water availability is a critical aspect of managing crop plants.Sumber: http://www.ctahr.hawaii.edu/mauisoil/a_comp04.aspxARTMOSFER TANAHThe soil atmosphere is not uniform throughout the soil because there can be localized pockets of air. The relative humidity of soil air is close to 100%, unlike most atmospheric humidity.Air in the soil often contains several hundred times more carbon dioxide.Sumber: http://www.ctahr.hawaii.edu/mauisoil/a_comp04.aspxKOMPONEN UTAMA TANAH ADALAH: Air, Udara, Rocks, Minerals, Nutrients, Organic Matter, Well-decomposed organic matter – Humus, OrganismsThe spaces between the solids are called pores. Good soil contains lots of these and is described as porus. This way air can easily circulate through the soil to reach plant roots and allow water to drain easily. The solid portion is mostly rock particles and bits of dead material and organic matter.Sumber: http://www.blogdivvy.com/growing-vegetables/what-is-soil.htmSIFAT OLAH TANAHSoil tilth is a measurement of the balance between basic soil elements: mineral, air, water and organic matter. The proper balance of these elements increases soil production by allowing efficient interaction of all the soil systems. Air and water balance in the soil is the key to good root growth.Sumber: http://rbmc.com.au/aerway.htmPORI DAN UDARA TANAHSoil pores, the voids between minerals, organic matter, and living organisms, are filled with air or water. There is a dynamic equilibrium between water and air content within a soil. When water enters the soil, it displaces air from some of the pores. 1. Composition of soil air2. Movement of gasses within soil 3. Soil porositySource: Lesley DampierSumber: http://www.landfood.ubc.ca/soil200/components/air.htmSumber: http://www.landfood.ubc.ca/soil200/interaction/water_air.htmKOMPOSISI UDARA TANAHThe composition of soil air is different from that of the atmosphere because it cannot readily mix with air above the soil. The metabolic activity of plant roots, microbes and soil fauna all affect the composition of soil air. For example, the concentration of carbon dioxide (CO2) in soil (between 0.3 and 3%) is often several hundred times higher than the 0.03% found in the atmosphere. In extreme cases oxygen can be as low as 5-10%, compared to 20% in the atmosphere. Soil air has a higher moisture content than the atmosphere, with relative humidity approaching 100% under optimum conditions. (humidity is not as variable in soil as it is in the atmosphere).  The amount and composition of air in soil are dynamic and to a large degree are determined by water content and activity of soil organisms. Sumber: http://www.landfood.ubc.ca/soil200/components/air.htmPERGERAKAN GAS DALAM TANAHAda dua mekanisme yang memfasilitasi pertukaran gas antara TANAH dan ATMOSFIR: 1)   MASS FLOW (convection) of air - the moving force is a gradient of total gas pressure, and it results in the entire mass of air streaming from a zone of higher pressure to one of lower pressure. Mass flow of air is much less important than diffusion, except perhaps in layers at or very near the soil surface. 2)   DIFFUSION - moving force is gradient of partial pressure of any constituent member of air to migrate from a zone of higher to lower pressure, even while air as a whole may remain stationary. In other words, through diffusion each gas moves in a direction determined by its own partial pressure. Sumber: http://www.landfood.ubc.ca/soil200/components/air.htmPERGERAKAN GAS DALAM TANAHThe oxygen flux density due to diffusion is proportional to the oxygen concentration gradient along the axis, and the proportionality factor is called the (oxygen) diffusion coefficient (D).  This statement is an example of Fick’s Law of Diffusion, which can be expressed as follows: J = - D dC/dXwhere J is the diffusive flux density of the gas (oxygen in this example) (mg/m2/s) along the x-axis, C is oxygen concentration in the soil air (units are g/m3), x is distance along x-axis (m), dC/dx is the oxygen concentration gradient (g/m4), and D is the (oxygen) diffusion coefficient (m2/s).  Sumber: http://www.landfood.ubc.ca/soil200/components/air.htmPERGERAKAN GAS DALAM TANAHThe oxygen diffusion coefficient (D) for diffusion in air is about 10,000 times as large as the coefficient for diffusion in water. Thus the oxygen diffusion coefficient (D) of a soil is very strongly influenced by three factors: 1)   air-filled porosity (Va/Vt), which decreases with increasing soil water content 2)   the continuity of air-filled pores, which decreases with increasing soil water content 3)   the tortuosity of air-filled pores, which increases with increasing soil water content. Growth of most plants and survival of their roots normally requires maintenance of adequate soil oxygen.  This in turn requires maintainance of soil water well below saturation, to enable rapid gas diffusion in the soil.  Sumber: http://www.landfood.ubc.ca/soil200/components/air.htmPOROSITAS TANAHSoil porosity (f) is the ratio of pore volume (Vf) to total soil volume (Vt) f = Vf / VtIt is general
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