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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 2011.

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Presentasi berjudul: "bahan kajian MK. DASAR ILMU TANAH UDARA TANAH DAN AERASI Oleh: Prof Dr.IR.Soemarno,M.S. Jurusan Tanah FP UB Nop 2011."— Transcript presentasi:

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2 bahan kajian MK. DASAR ILMU TANAH UDARA TANAH DAN AERASI Oleh: Prof Dr.IR.Soemarno,M.S. Jurusan Tanah FP UB Nop 2011

3 AERASI TANAH 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 optimum Tanah 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 optimum Tanah yang AERASI nya baik mempunyai sifat: 1. Harus ada ruangan yang cukup tanpa bahan mineral dan air 2. Harus ada kesempatan yg cukup bagi gas-gas untuk keluar-masuk ruangan tsb Dua 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 CO2

4 MASALAH AERASI TANAH Air Tanah yang berlebihan 1. Tanah jenuh air, tanah tergenang dapat berpengaruh buruk pd tanaman pd umumnya 2.Biasanya pd tanah-tanah yg drainasenya buruk dan tekstur halus 3. Pada tempat-tempat cekungan PERTUKARAN 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 gas Penyebab buruknya aerasi tanah: 1. Kandungan air tanah yg berlebihan shg tidak menyisakan ruangan untuk gas/ udara 2. Pertukaran gas tidak cukup cepat unt mempertahankan kadarnya pd tingkat tertentu.

5 LAJU DIFUSI OKSIGEN (LDO) Nilai LDO semkin kecil dengan kedalaman tanah LDO pada kedalaman 95 cm sama dengan setengah nilai LDO pd kedalaman 11.5 cm Pertumbuhan akar tanaman berhenti bila LDO turun menjadi 20 g x cm 2 /menit LDO adalah laju pergantian oksigen dalam tanah yg dipakai oleh akar tanaman yg bernafas atau digantikan oleh air.

6 SUSUNAN UDARA TANAH % volume: TempatO2CO2N2 Udara tanah: New York Inggris Udara Atmosfer Inggris Sumber: Lyon, Buckman & Brady, 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

7 Faktor Susunan Udara Tanah Tanah lapisan atas vs Tanah lapisan bawah Jumlah total ruangan pori tanah lapisan bawah lebih sedikit dibanding tanah lapisan atas % CO2 udara tanahKedalaman sampling, cm 0.5 gandum + rabuk 30 tanah bera + rabuk kandang Lempung liat berdebu Lempung berdebu tanah bera 180 Waktu sampling % O2 udra tnh Susunan udara tanah tgt pada: 1. Jumlah ruangan / pori yg tersedia 2. Kecepatan reaksi biokimia 3. Pertukaran gas Penambahan bahan organik akan mengubah susunan udara tanah

8 AERASI & KEGIATAN BIOLOGIS Aerasi b uruk mempengaruhi Tanaman: 1. Pertumbuhan perakaran sangat terbatas 2.Penyerapan hara terhambat 3.Air menjadi berkurang 4.Pembentukan senyawa anorganik yang bersifat toksik Jasad Mikro 1. Aerasi buruk menurunkan oksidasi bahan organik tanah 2. Penurunan ini lebih disebabkan oleh kekurangan O2 3. Populasi jasad renik sangat terpengaruhi olh aerasi 4. Aerasi buruk mendorong aktifitas jasad anaerob dan fakultatif, menghasilkan senyawa reduksi, fero, mangano, sulfida Akar tanaman apel memerlukan minimal 3% O2 dalam udara tanah, sedangkan % 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 g x /cm2/menit.

9 AERASI & EFEK LAIN Tanaman TeksturLDO pada kedalaman: Kondisi 10 cm 20 cm 30 cm pertumbuhan tanaman Brokoli Lempung533138Sangat baik Selada Lempung berdebu492632Baik Phaseolus sp Lempung272725Klorosis Arbei Lempung berpasir363234Klorosis Kapas Lemping berliat79-Klorosis Jeruk Lempung berpasir Pertumbuhan akar cepat Sumber: Stolzy dan Letey, Dekomposisi anaerobik C6H12O6 3CO2 + 3 CH4 gula metan Kondisi aerasi tanah berpengaruh terhadap bentuk unsur hara penting: UnsurKondisi OksidasiKondisi reduksi (tergenang) KarbonCO2CH4 NitrogenNO3-N2, NH4+ BelerangSO4=H2S, S=

10 AERASI & KEGIATAN Pengelolaan Adaptasi 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 tanah 2.Pengelolaan tanaman ditentukan oleh baik-buruknya aerasi tanah Tindakan untuk memperbaiki aerasi ntanah: 1. Menghilangkan air yang berlebihan (drainase) 2. Memperbaiki agregasi dan pengolahan tanah

11 SUHU TANAH Suhu tanah di lapangan ditentukan oleh: 1.Jumlah panas yang diserap oleh tanah 2.Energi panas yg diperlukan untuk mengubah suhu tanah 3.Energi yg diperlukan untuk evaporasi yg terus menerus di permukaan tanah Suhu 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 oC Sumber: Amplitude of seasonal soil temperature change as a function of depth below ground surface.

12 SERAPAN & KEHILANGAN PANAS Kehilangan panas dari tanah ke atmosfer, melalui KONDUKSI dan RADIASI Radiasi ini berupa infra merah, tidak terlihat mata, gelombang gelap Radiasi gelombang gelap ini berenergi tinggi dan selama pemancarannya banyak panas yg hilang dari tanah Jumlah panas yg diserap tanah ditentukan oleh radiasi efektif yg mencapai permukaan tanah dan iklim Jumlah energi yg masuk tanah dipengaruhi oleh: 1. Warna tanah: gelap menyerap lebih banyak energi 2. Lereng: 3. Tanaman penutup tanah: Hutan vs. tanah gundul Tanah gundul lebih cepat memanas dan mendingin Thermal 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.. Thermal Admittance Source: Lesley Dampier

13 PANAS JENIS TANAH Thermal 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: Jumlah panas yang diperlukan oleh satu gram tanah untuk menaikkan suhunya satu derajat celcius. Panas jenis tanah kering lebih rendah dibandingkan dg tanah basah Tanah kering: PJ = 0.20 Kadar air 20%: PJ = 0.33 Kadar air 30%: PJ = 0.38 Thermal Conductivity Source: Lesley Dampier

14 PANAS PENGUAPAN Warna tanah vs. Suhu Tanah gelap biasanya kaya bahan organik dan kandungan airnya tinggi. Tanah gelap yg drainasenya buruk lambat memanas. Penguapan air tanah memerlukan sejumlah energi panas Untuk menguapkan 1 g air pada 20oC diperlukan panas 585 kalori. Penguapan 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. Soil Heat Capacity (Cv): Amount of heat needed to cause a 1oC change in temperature of a unit volume of soil. Heat Capacity Source: Lesley Dampier 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

15 GERAKAN PANAS DALAM TANAH Proses konduksi panas dalam tanah berlangsung lambat. Tanah lapisan bawah suhunya lebih rendah dp tanah lapisan atas. Perubahan suhu tanah lapisan bawah sangat sedikit sekali Energi 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 udara Thermal 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 capacity Heat Capacity Source: Lesley Dampier

16 SUHU TANAH Suhu tanah. oC Soil depth cm 60 Januari Juli 300Sumber: Fluker, 1956 (Texas) Suha tanah pada suatu saat tergantung pada nisbah energi panas yang diserap dan yang hilang Suhu tanah juga tergantung kedalaman tanah

17 Pengendalian Suhu Tanah Suhu oC Kedalaman tanah 1.5 cm Kedalaman tanah 15 cm 38 tanpa mulsa Dengan mulsa Tanpa mulsa Dengan mulsa pagisore pagi sore Penggunaan mulsa organik mengakibatkan suhu tanah lebih rendah dan lebih merata Pengelolaan air tanah secara tepat juga akan mempengaruhi suhu tanah

18 AERASI 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 redoks Micropores (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:

19 ‘Goose’ Your Lawn for Good Soil Health By Shayne Hale June 2, 2011 Aeration 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:

20 Lawn Aeration for a Greener, Thicker, Healthier Lawn! Umber: More Benefits of Lawn Aeration Aeration 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.

21 Sumber: organicsoilsolutions.com Pemadatan tanah berarti tanah menjadi lebih padat, porositasnya berkurang, sehingga jumlah dan pergerakan udara dalam tanah juga terbatas. Hal ini dapat mengganggu pertumbuhan akar tanaman

22 Mechanism of Gas Exchange in Soils: Mencegah defisiensi O 2 atau toksisitas CO 2 Sumber; Mekanisme pergerakan gas Mass Flow Movement of a mass of air (gases move together Driven 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?) Diffusion Each gas moves down gradients of its own concentration Even with no overall pressure difference O 2 and CO 2 diffusing past each other in opposite directions

23 Function of concentration gradient and resistance Resistance: Increases with reductions in pore size O 2 gradient: Decreases with depth due to O 2 consumption Gradient decreases with depth; less ODR. O 2 Diffusion rate (ODR) : Rate of movement across a cross- sectional area ; ug O 2 /cm 2. minute Sumber;

24 Faktor-faktor yang mempengaruhi Aerasi Sumber; 1.Excess Moisture - diffusion of water very slow through water 2.Soil texture - heavy soils - reduced pore size, greater resistance 3.Poor Structure - macropores increase ODR 4.Position on Slope - excess moisture at bottom 5. Impermeable Layers 6.Soil Depth - subsoils farther away from surface (less ODR) 7. Rate of O 2 consumption (high labile OM content)

25 POTENSIAL REDOKS (Eh) Sumber; 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.

26 Structure 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).www.sinauer.comwww.whfreeman.com SUMBER: Posisi dan lokasi udara dalam pori, di dalam struktur tanah Macropores (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.

27 TEKSTUR TANAH: THE KEY TO MANAGEMENT OF SOIL – PLANT – WATER RELATIONSHIP.SUMBER: Soil 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.

28 Perbandingan antara komposisi udara tanah dan atmosfir Sumber:

29 Kandungan O2 dan CO2 pada berbagai kedalaman tanah (Trinidad) Sumber:

30 UDARA TANAH Air 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: 1.An increase in soil water content often causes a reduction in soil aeration. 2.Likewise, reducing soil water content may mean an increase in soil aeration. 3.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:

31 ARTMOSFER TANAH The 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:

32 KOMPONEN UTAMA TANAH ADALAH: Air, Udara, Air, Udara, Rocks, Minerals, Nutrients, Organic Matter, Well- decomposed organic matter – Humus, Organisms The spaces between the solids are called pores. Good soil contains lots of these and is described as porus.soil This way air can easily circulate through the soil to reach plant roots and allow water to drain easily.soilwater The solid portion is mostly rock particles and bits of dead material and organic matter. Sumber:

33 SIFAT OLAH TANAH Sumber: Soil 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.

34 PORI DAN UDARA TANAH Sumber: ents/air.htm Soil 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 air 2. Movement of gasses within soil 3. Soil porosity Sumber: on/water_air.htm Source: Lesley Dampier

35 KOMPOSISI UDARA TANAH Sumber: The 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 (CO 2 ) 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.

36 PERGERAKAN GAS DALAM TANAH Sumber: Ada 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.

37 PERGERAKAN GAS DALAM TANAH Sumber: The 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/dX where J is the diffusive flux density of the gas (oxygen in this example) (mg/m 2 /s) along the x-axis, C is oxygen concentration in the soil air (units are g/m 3 ), x is distance along x-axis (m), dC/dx is the oxygen concentration gradient (g/m 4 ), and D is the (oxygen) diffusion coefficient (m 2 /s).

38 PERGERAKAN GAS DALAM TANAH Sumber: The 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 (V a /V t ), 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.

39 POROSITAS TANAH Sumber: Soil porosity (f) is the ratio of pore volume (V f ) to total soil volume (V t ) f = V f / V t It is generally between 30-60%. Porosity tells us nothing about the relative amounts of large and small pores, and should be interpreted with caution. Generally, high porosity (e.g. 60%) is an indicator of lack of compaction and good soil conditions.

40 KOMPOSISI UDARA TANAH Sumber: The soil air contains a number of gases of which nitrogen, oxygen, carbon dioxide and water vapour are the most important. Soil air constantly moves from the soil pores into the atmosphere and from the atmosphere into the pore space. Soil air and atmospheric air differ in the compositions. Soil air contains a much greater proportion of carbon dioxide and a lesser amount of oxygen than atmospheric air. At the same time, soil air contains a far great amount of water vapour than atmospheric air. The amount of nitrogen in soil air is almost the same as in the atmosphere.

41 FAKTOR YANG MEMPENGARUHI KOMPOSISI UDARA TANAH Sumber: SIFAT DAN KONDISI TANAH: The quantity of oxygen in soil air is less than that in atmospheric air. The amount of oxygen also depends upon the soil depth. The oxygen content of the air in lower layer is usually less than that of the surface soil. This is possibly due to more readily diffusion of the oxygen from the atmosphere into the surface soil than in the subsoil. Light texture soil or sandy soil contains much higher percentage than heavy soil. The concentration of CO2 is usually greater in subsoil probably due to more sluggish aeration in lower layer than in the surface soil.

42 FAKTOR YANG MEMPENGARUHI KOMPOSISI UDARA TANAH Sumber: JENIS TANAMAN: Plant roots require oxygen, which they take from the soil air and deplete the concentration of oxygen in the soil air. Soils on which crops are grown contain more CO2 than fallow lands. The amount of CO2 is usually much greater near the roots of plants than further away. It may be due to respiration by roots.

43 FAKTOR YANG MEMPENGARUHI KOMPOSISI UDARA TANAH Sumber: AKTIVITAS MIKROBA TANAH: The microorganisms in soil require oxygen for respiration and they take it from the soil air and thus deplete its concentration in the soil air. Decomposition of organic matter produces CO2 because of increased microbial activity. Hence, soils rich in organic matter contain higher percentage of CO2.

44 FAKTOR YANG MEMPENGARUHI KOMPOSISI UDARA TANAH Sumber: VARIASI MUSIMAN: The quantity of oxygen is usually higher in dry season than during the monsoon. Because soils are normally drier during the summer months, opportunity for gaseous exchange is greater during this period. This results in relatively high O2 and low CO2 levels. Temperature also influences the CO2 content in the soil air. High temperature during summer season encourages microorganism activity which results in higher production of CO2.

45 GAS DALAM TANAH The air space in soil contains oxygen to provide for respiration of plant roots and soil organisms. This air space could also contain carbon dioxide as a product of respiration of plant roots and soil organisms.soiloxygenrespirationrootscarbon dioxide KomposiSI UDARA dalam TANAH dan atmosphere:atmosphere NitrogenNitrogen: Soil Air: 79.2% Atmosphere: 79.0% OxygenOxygen: Soil Air: 20.6% Atmosphere: 20.9% Carbon DioxideCarbon Dioxide: Soil Air: 0.25% Atmosphere: 0.03% Gas molecules in soil are in continuous thermal motion according to the kinetic theory of gases, there is also collision between molecules - a random walk.kinetic theory of gasesrandom walk In soil, a concentration gradient causes net movement of molecules from high concentration to low concentration, this gives the movement of gas by diffusion.diffusion Numerically, it is explained by Fick's law of diffusion.Fick's law of diffusion Soil gas includes air, water vapour and the pollutants that might be picked up from the soil underneath a building and carried by air leakage into the building.air leakage Sumber: Russell, E. J.; Appleyard, A.. (1915). "The Atmosphere of the Soil: Its Composition and the Causes of Variation". The Journal of Agricultural Science 7: 1.

46 UDARA TANAH


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