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1 Bahan kajian pada MK Dasar Ilmu Tanah KEMASAMAN TANAH DAN PENGAPURAN Diabstraksikan Oleh: Smno.jursntnhfpub.DES2012.

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Presentasi berjudul: "1 Bahan kajian pada MK Dasar Ilmu Tanah KEMASAMAN TANAH DAN PENGAPURAN Diabstraksikan Oleh: Smno.jursntnhfpub.DES2012."— Transcript presentasi:

1 1 Bahan kajian pada MK Dasar Ilmu Tanah KEMASAMAN TANAH DAN PENGAPURAN Diabstraksikan Oleh: Smno.jursntnhfpub.DES2012

2 WHAT IS SOIL pH? Diunduh dari: ………… 11 sept 2012. pH tanah merupakan indikator kemasaman atau kebasaan suatu tanah. Kondisi kemasaman atau kebasaan yang ekstrim mempengaruhi pertumbuhan tanaman. Some plants can grow over a wide range of pH; others are sensitive to acidity, or alkalinity. It is hard to overestimate the importance of pH in agricultural systems. Soil pH is affected by soil chemistry and soil biology. Further, it is affected by the physical characteristics of the soil via the aeration of soil and soil water.

3 HOW DOES SOIL pH AFFECT PLANT GROWTH? Kondisi ideal kemasaman tanah bagi kebanyakan tanaman adalah agak masam atau agak alkalis. At extreme pH the availability of some nutrients is decreased, e.g. phosphorus and molybdenum at low pH, and zinc at high pH; and the solubility of elements toxic to plants is increased, e.g. aluminium and manganese at low pH. Extremes in alkalinity and acidity present problems for the production of many agriculturally important plant species and their symbiotic Rhizobia. Due to the complexity of soil chemistry, it has often been difficult to confidently identify the cause of poor plant growth or nodulation. Diunduh dari: ………… 11 sept 2012.

4 pH TANAH Diunduh dari:………… 11 Des 2012. pH tanah merupakan ukuran kemasaman atau kebasaan suatu tanah. pH didefinisikan sebagai logaritma negatif (base 10) aktivitas kation hidrogen (H + atau, H 3 O+ aq) dalam sistem larutan. It ranges from 0 to 14, with 7 being neutral. A pH below 7 is acidic and above 7 is basic. Soil pH is considered a master variable in soils as it controls many chemical processes that take place. It specifically affects plant nutrient availability by controlling the chemical forms of the nutrient. The optimum pH range for most plants is between 5.5 and 7.0, [1] however many plants have adapted to thrive at pH values outside this range. [1] (1). Perry, Leonard. “pH for the Garden". 11 December 2012.

5 KLASIFIKASI KISARAN pH TANAH Diunduh dari:………… 11 Des 2012. The United States Department of Agriculture Natural Resources Conservation Service, formerly Soil Conservation Service classifies soil pH ranges as follows: DenominationpH range Ultra acid< 3.5 Extreme acid3.5–4.4 Very strong acid4.5–5.0 Strong acid5.1–5.5 Moderate acid5.6–6.0 Slight acid6.1–6.5 Neutral6.6–7.3 Slightly alkaline7.4–7.8 Moderately alkaline7.9–8.4 Strongly alkaline8.5–9.0 Very strongly alkaline> 9.0

6 SUMBER KEMASAMAN TANAH Diunduh dari:………… 11 Des 2012. Acidity in soils comes from H + and Al 3+ ions in the soil solution and sorbed to soil surfaces. While pH is the measure of H + in solution, Al 3+ is important in acid soils because between pH 4 and 6, Al 3+ reacts with water (H 2 O) forming AlOH 2+, and Al(OH) 2 +, releasing extra H + ions. Every Al 3+ ion can create 3 H + ions. Many other processes contribute to the formation of acid soils including rainfall, fertilizer use, plant root activity and the weathering of primary and secondary soil minerals. Acid soils can also be caused by pollutants such as acid rain and mine spoilings. 1.Rainfall: Acid soils are most often found in areas of high rainfall. Excess rainfall leaches base cation from the soil, increasing the percentage of Al 3+ and H + relative to other cations. Additionally, rainwater has a slightly acidic pH of 5.7 due to a reaction with CO 2 in the atmosphere that forms carbonic acid. 2.Fertilizer use: Ammonium (NH 4 + ) fertilizers react in the soil in a process called nitrification to form nitrate (NO 3 − ), and in the process release H + ions.

7 Diunduh dari:………… 11 Des 2012. 3.AKTIVITAS AKAR TUMBUHAN: Plants take up nutrients in the form of ions (NO 3 −, NH 4 +, Ca 2+, H 2 PO 4 −, etc.), and often, they take up more cations than anions. However plants must maintain a neutral charge in their roots. In order to compensate for the extra positive charge, they will release H + ions from the root. Some plants will also exude organic acids into the soil to acidify the zone around their roots to help solubilize metal nutrients that are insoluble at neutral pH, such as iron (Fe).cationsanions 4.PELAPUKAN MINERAL: Both primary and secondary minerals that compose soil contain Al. As these minerals weather, some components such as Mg, Ca, and K, are taken up by plants, others such as Si are leached from the soil, but due to chemical properties, Fe and Al remain in the soil profile. Highly weathered soils are often characterized by having high concentrations of Fe and Al oxides. 5.HUJAN ASAM: When atmospheric water reacts with sulfur and nitrogen compounds that result from industrial processes, the result can be the formation of sulfuric and nitric acid in rainwater. However the amount of acidity that is deposited in rainwater is much less, on average, than that created through agricultural activities. 6.Mine Spoil: Severely acidic conditions can form in soils near mine spoils due to the oxidation of pyrite. SUMBER KEMASAMAN TANAH

8 pH TANAH & KETERSEDIAAN HARA Diunduh dari:………… 11 Des 2012. Nutrients needed in large amounts by plants are referred to as macronutrients and include nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg) and sulfur (S). Elements that plants need in trace amounts are called trace nutrients or micronutrients. Trace nutrients are not major components of plant tissue but are essential for growth. They include iron (Fe), manganese (Mn), zinc (Zn), copper (Cu), cobalt (Co), molybdenum (Mo), and boron (B). nitrogenphosphoruspotassiumsulfurironzinccoppercobaltmolybdenumboron Both macronutrient and micronutrient availability are affected by soil pH. In slightly to moderately alkaline soils, molybdenum and macronutrient (except for phosphorus) availability is increased, but P, Fe, Mn, Zn Cu, and Co levels are reduced and may adversely affect plant growth. In acidic soils, micronutrient availability (except for Mo and Bo) is increased. Nitrogen is supplied as ammonium (NH 4 ) or nitrate (NO 3 ) in fertilizer amendments, and dissolved N will have the highest concentrations in soil with pH 6–8. Concentrations of available N are less sensitive to pH than concentration of available P. In order for P to be available for plants, soil pH needs to be in the range 6.0 and 7.5. If pH is lower than 6, P starts forming insoluble compounds with iron (Fe) and aluminium (Al) and if pH is higher than 7.5 P starts forming insoluble compounds with calcium (Ca). Nutrient availability in relation to soil pH. Most nutrient deficiencies can be avoided between a pH range of 5.5 to 6.5, provided that soil minerals and organic matter contain the essential nutrients to begin with.

9 TANAMAN & pH TANAH Diunduh dari:………… 11 Des 2012. 1.pH 4.5–5.0 Blueberry, Bilberry, Heather, Cranberry, Orchid, Azalea, for blue Hydrangea (less acidic for pink), Sweet Gum, Pin Oak. 2.pH 5.0–5.5 Parsley, Potato, Heather, Conifers, Pine, Sweet Potato, Maize, Millet, Oars, Tye, Radish, Ferns, Iris, Orchids, Rhododendron, Camellia, Daphne and Boronia. 3.pH 5.5–6.0 Bean, Brussels Sprouts, Carrot, Choko, Endive, Kohl Rabi, Peanuts, Rhubarb, Soybean, Crimson Clover, Aster, Begonia, Canna, Daffodil, Jonquil, Larkspur, Petunia, Primrose, Violet and most bulbs.Brussels SproutsCarrotAster 4.pH 6.0–6.5 Broccoli, Cabbage, Cannabis, Cauliflower, Cucumber, Aubergine, Pea, Sweet Corn, Pumpkin, Squash, Tomato, Turnip, Red Clover, Sweet Clover, White Clover, Candytuft, Gladiolus, Iceland Poppy, Pansy, Rose, Snapdragon, Viola, Wallflower, Zinnea and Strawberry.Rose 5.pH 6.5–7.0 Asparagus, Beet, Celery, Lettuce, Melons, Onion, Parsnip, Spinach, Alfalfa, Carnation, Chrysanthemum, Dahlia, Stock, Sweet Pea and Tulip. 6.pH 7.1–8.0 Lilac, brassica.

10 What is an optimum soil pH? Most nutrients are at their maximum availability in slightly acidic, neutral or slightly alkaline soils. At the same time, most phytotoxic forms of aluminium and manganese are at their minimum concentration in this pH range. Emil Truog did some outstanding work over 60 years ago and his conclusions on how pH affects the availability of nutrients are still widely used today. Diunduh dari: ………… 11 sept 2012.

11 How to measure soil pH? Soil pH may be measured on site using a colorimetric kit and a fresh sample. More reliably, it can be measured in a laboratory, using a prepared sample and a pH probe. As pH is usually measured as one of a suite of soil tests to assess fertility, the laboratory option is quite practical. How does soil pH vary with depth? pH varies within the soil profile. The pH of the whole soil profile or any horizon cannot be predicted by measuring surface soil pH. An undesirable pH in a lower soil horizon can constrain plant growth. Diunduh dari: ………… 11 sept 2012.

12 How the soil pH can be changed? The most common way of increasing soil pH is applying agricultural lime. It is, however, an activity that requires a good application of science to be both effective and economic. Successful use of lime occurs where the farmer: 1.Knows the target pH for the plants being grown 2.Incorporates lime by cultivation 3.Matches the quantity and quality of lime with amount needed for the pH buffering capacity of the soil 4.Can get it on the ground at a sufficiently cheap price (i.e. including transport and spreading costs) Management decisions on the application of lime must consider many factors. Aside from business objectives, important factors include: 1.Jenis Kapur = The type of lime 2.its effective neutralising value (a product of fineness and composition) 3.the moisture content of the lime 4.application method 5.depth of soil to be ameliorated 6.soil texture (e.g. coarse textured soils like sands need less lime than fine textured soils) matter content (e.g. low organic matter content soils require less lime to ameliorate acidity than peaty soils) 8.Waktu = timing 9.Respon tanaman = plant response 10.Biaya = cost Diunduh dari: ………… 11 sept 2012.

13 Does soil pH change with time (and should I worry)? Agricultural practices often decrease the pH of soil (i.e. acidification). An animation shows some of the ways acidification may occur is available. The practices that often cause acidification 1.Sowing annual dominant pastures 2.Cropping with legumes (in horticulture and broad-acre cropping) 3.Application of N fertilisers (including liquid N and by N applied by fertigation) 4.Product removal, especially hay and grain There is therefore an imperative to monitor pH changes and take action to remediate as required. In some instances, soil acidification has affected the subsoil as well as the surface soil. This presents difficulties for farmers as it is not easy to ameliorate acidified subsoils. Lime does not readily move down the profile. Diunduh dari: ………… 11 sept 2012.

14 SEKALA pH TANAH Hydrogen ion concentration in the soil is measured in terms of the pH scale. Soil pH ranges from 3 to 10. Pure water has a pH of 7 which is considered neutral, pH values greater than seven are considered basic or alkaline, below seven acidic. Most good agricultural soils have a pH between 5 and 7. Though acidic soils pose a problem for agriculture due to their lack of nutrients, alkaline soils can pose a problem as well. Alkaline soils may contain appreciable amounts of sodium that exceed the tolerances of plants, contribute to high bulk density and poor soil structure. Alkaline soils are common in semiarid regions. Diunduh dari:

15 pH TANAH & KETERSEDIAAN HARA Diunduh dari: Soil Reaction (pH) From an agricultural standpoint pH is important because it strongly affects plant growth, nutrient availability,element al toxicity and microbial activity. In an agricultural sense, soil pH indirectly affects plant growth.

16 pH DAN PERTUMBUHAN TANAMAN Diunduh dari: Soil pH is a measurement of the acidity or alkalinity of a soil. On the pH scale, 7.0 is neutral. Below 7.0 acid, and above 7.0is basic or alkaline. A pH range of 6.8 to 7.2 is termed near neutral. Areas of the world with limited rainfall typically have alkaline soils while areas with higher rainfall typically have acid soils. pH Ranges and influence on plant growth potential - 7.0 is neutral. Above 7.0 is alkaline Below 7.0 is acid.

17 17 EMPAT KOMPONEN TANAH Padatan An-organik: Mineral & Bukan mineral Padatan Organik : Bahan Organik Tanah (Senyawa organik mati) Organisme hidup Udara tanah …… Aerasi Tanah Air tanah = Larutan tanah Soil Solution, Elektrolit tanah Sifat fisiologik penting dari Larutan tanah adalah “REAKSINYA” (pH) ……. Kemasaman / kebasaan tanah

18 18 pH = - log [H + ] [H + ] dlm larutan tanah ………. Kemasaman aktif [H + ] dijerap koloid tanah ………. Kemasaman potensial Total keduanya ………………….. Kemasaman total Kisaran Nilai pH tanah: 0 - 14 pH = 7.0 : Tanah Netral pH < 7.0 : Tanah Masam pH > 7.0 : Tanah basa/ Alkalin/Alkalis Biasanya: Tanah masam : di daerah iklim basah Tanah alkalis: di daerah kering Misel -H [H + ] Ion H + terjerap, H dd Ion H + terlarut

19 19 Kation aluminium: MISEL Al Al 3+ Al 3+ + H 2 O Al(OH) 2+ + H + Al 3+ + OH - Al(OH) 2+ Al(OH) 2+ + OH - Al(OH) 2 + Al(OH) 2+ + H 2 O Al(OH) 2 + + H + Al(OH) 2 + + H 2 O Al(OH) 3 + H + SUMBER KEMASAMAN TANAH H dd H+ Bahan Organik Tanah:

20 20 pH & Ketersediaan Hara Ca dan Mg: Ketersediaan maksimum: pH = 6 - 8.5 Ketersediaan minim pada tanah dg : pH < 4.0 N, K dan S: Ketersediaan maksimum: pH > 6 Ketersediaan minim pada tanah dg : pH < 4.0 Fosfat : Ketersediaan maksimum: pH = 6 - 7.5 Ketersediaan minim pada tanah dg : pH < 4.0 Fe, Mn,Zn, Cu,Co : Ketersediaan maksimum: pH < 5.5 Ketersediaan minim pada tanah dg : pH > 7.5 Bakteri & Aktinomisetes : Ketersediaan maksimum: pH > 5.5 Ketersediaan minim pada tanah dg : pH < 4.0 Mo: Ketersediaan maksimum pd pH > 6.5

21 21 Problem Kemasaman Tanah Kesuburan tanah Ketersediaan Unsur Hara Suasana fisiologis larutan tanah tidak sesuai bagi proses-proses pertumbuhan akar tanaman Keracunan unsur hara mikro Gangguan akibat tingginya ketersediaan/kelarutan kation aluminium Menurunkan kemasaman tanah = Menaikkan pH tanah = ………….. Pengapuran Gangguan kehidupan jasad renik tanah

22 22 Al dd dan % KEJENUHAN Al 1. Sumber kemasaman tanah : H+, H dd, Al dd, 2. Al dd diendapkan pada pH > 5.5 - 6.0 3. % kejenuhan Al dari KTK efektif menjadi ukuran kemasaman tanah 4. Kejenuhan basa (KB) = jumlah basa dibagi KTK 5. Al dd ditentukan dengan jalan ekstraksi tanah dg 1 N KCl, dan mentitrasi ekstraksnya dengn larutan basa 6.

23 23 HUBUNGAN pH dan KEJENUHAN Al 10 20 30 40 50 60 70 % kejenuhan Al pH tanah 5.4 5.1 4.8 4.5 4.2 3.9 Sumber: Abruna et al. 1975 Ultisols & Oxisols

24 24 HUBUNGAN KEJENUHAN Al dan HASIL BEANS 10 20 30 40 50 60 70 % kejenuhan Al % hasil maks. 100 80 60 40 20 0 Sumber: Abruna et al. 1975 Ultisols & Oxisols r = 0.93**

25 25 1. Konsentrasi Al dlm larutan tanah > 1 ppm menyebabkan penurunan hasil tanaman 2.Tembakau dan kentang sangat peka thd Al +++ dlm tanah, terutama akarnya. Gejalanya akar menjadi tebal, kaku dan becak-becak jaringan mati 3.Pertumbuhan akar jagung mulai terganggu pada kondisi 60% kejenuhan Al. 4.Al cenderung terakumulasi dalam akar dan menghambat penyerapan dan translokasi Ca dan fosfat menuju tajuk, sehingga mendorong defisiensi Ca dan P.

26 26 1. Gangguan pertumbuhan tanaman pd tanah masam dapat juga disebabkan oleh defisiensi Ca dan/atau Mg 2.Gangguan akar tembakau pd Ultisol yg tidak dikapur disebabkan oleh keracunan Al dan defisiensi Ca. 3.Kalau Al diendapkan (dg menggunakan MgCO3) dan tidak ditambahkan Ca, pertumbuhan akar tembakau akan berhenti dalam waktu 60 jam. 4.Tanah masam di daerah tropis defisien Ca tanpa menunjukkan masalah toksisitas Al. 5.Misalnya Tanah masam di Hawaii, pH < 5.0, namun Al dd nya sedikit; pengapuran berfungsi seperti pemupukan Ca 6.Tanah masam di Brazil sangat miskin Mg dan respon positif thd pupuk Mg.

27 27 TOKSISITAS Al & DEFISIENSI Ca thd AKAR TEMBAKAU 1 2 3 waktu (hari) % maks. pemanjangan akar 100 80 60 40 20 0 Sumber: Abruna et al. 1975 Ultisols & Oxisols Dikapur CaCO3, pH 5.8, 4.4 meq Ca++ Dikapur MgCO3, pH 5.6, 0.4 meq Ca++ Tdk Dikapur, pH 4.2, 0.4 meq Ca++

28 28 EFEK Al thd PERTUMBUHAN AKAR TanahpHAl dd % Kejenuhan Berat kering akar tanaman: me/100 g Al Jagung (mg/pot)Sorghum Ultisol 4.8 4 40931400 4.5 6 57874296 3.9 11 87209 19 Oxisol 4.8 3 52687345 4.5 4 70630126 4.0 5 87389128 Sumber: Brenes & Pearson, 1973.

29 Measurement of soil pH: Problems and solutions M. E. Sumner Communications in Soil Science and Plant Analysis Volume 25Volume 25, Issue 7-8, 1994. Special Issue: 1993 International Symposium on Soil Testing and Plant Analysis: Precision Nutrient Management Part IIssue 7-8 Diunduh dari: pH measurements in soil systems present unique challenges in terms of the interpretation of the values obtained. The principles behind the glass/calomel electrode system are discussed as a backdrop to pH measurements in both pure solutions and soils. The influence of the liquid junction potential and salt concentration on the pH values of soil water suspensions are discussed in detail from which it emerges that the current practice of measuring soil pH in stirred soil suspensions is likely to result in the greatest errors being incurred. This is due to the large liquid junction potential of uncertain magnitude developed in such systems. Measurements in salt solutions, such as M KCl and 0.1 M CaCl 2, reduce the magnitude of the liquid junction potential substantially and make the pH values obtained more reproducible and consistent. The position of the calomel electrode salt bridge is crucial in measuring soil pH and should always be positioned in the clear supernatant solution.

30 Relationships between Soybean Yield, Soil pH, and Soil Carbonate Concentration Natalia P. Rogovska, Alfred M. Blackmer and Antonio P. Mallarino SSSAJ. Vol. 71 No. 4, p. 1251-1256. July, 2007 Diunduh dari: Soybean [Glycine max (L.) Merrill] often shows symptoms of iron deficiency chlorosis (IDC) on high pH, calcareous soils of the U.S. Midwest. The objective of this study was to assess the variation in soybean yield that could be explained by soil pH and carbonate concentration in Iowa fields. Color aerial images of soybean canopy taken from 2000 to 2002 from 12 fields having acid to calcareous soils were used to select 10 to 28 sampling areas 10 to 25 m 2 in size to encompass significant variability in early soybean growth and IDC symptoms in each field. Representative areas 0.93 m 2 in size were identified through field observations to collect soil samples and measure grain yield. Soil pH measured to a 15-cm depth across fields ranged from 5.6 to 8.2 and calcium carbonate equivalent (CCE) ranged from 0 to 30%. Soil CCE varied from 2.5 to 30% as pH ranged from 7.7 to 8.2. Grain yield decreased with increasing pH and CCE in 9 and 11 fields, respectively. Soil pH and CCE explained 30 and 41% of the variability in relative yield across sites, respectively. An alkalinity stress index (ASI) that combined both measurements (pH + 0.14CCE) was developed based on the relative effects of each measurement on yield and explained 45% of the yield variability across sites. The index developed was a better predictor of soybean yield in fields with high-pH soils than each measurement alone.

31 Rapid Measurement of Soil pH Buffering Capacity D. E. Kissel, L. S. Sonon and M. L. Cabrera SSSAJ. Vol. 76 No. 2, p. 694-699. Mar, 2012 Diunduh dari: Soil pH buffering capacity, described here as lime buffer capacity (LBC), is a fundamental soil property needed to estimate the change in soil pH after a known quantity of acidity or alkalinity is added to soil. Its rapid determination can be useful for many purposes, for example, estimating the lime needed to raise pH or acid needed to lower pH to a desired level. The objective of the present study was to evaluate the statistical relationship developed in previous studies between LBC from 30-min equilibration with Ca(OH) 2 (LBC 30 ) and LBC from 5-d equilibration with Ca(OH) 2 (LBC eq ) on a larger set of soils from Georgia. Five days was considered adequate time for true pH equilibrium and obtaining a true LBC. Eighty-seven soils from Georgia were treated with Ca(OH) 2 using standard procedures for both equilibrium times, and the statistical relationship between the two LBCs were developed. The relationship developed in the first study was further tested in a second incubation of 67 soils to determine its accuracy in achieving a target pH CaCl2 of 6.0. The data from the second incubation indicated that the target pH was exceeded by an average of 0.11 pH units and that the average pH spread around the acquired pH was ±0.1 pH unit. The results suggest that the prediction of soil pH buffering capacity based on the proposed protocols will be sufficiently accurate for making agricultural lime application recommendations.


33 33 BENTUK BAHAN KAPUR Kapor Oksida: Kapur Sirih Kemurniannya: 85 - 95% Pembuatannya: CaCO3 + panas CaO + CO2 CaMg(CO3)2 + panas CaO +MgO + CO2 Reaksinya dlm tanah: MISEL - H + CaO MISEL - Ca + H2O CaO + H2O Ca(OH)2 Ca(OH)2 + 2 H 2 CO 3 Ca(HCO 3 ) 2 + 2 H2O % Oksida CaO : 77% Ekuivalen oksida Ca: 102 Daya netralisasi: 182.1 (kesetaraan CaCO3) Persentase unsur Ca: 55 % Oksida MgO : 18% Persentase unsur Mg: 10.8

34 34 BENTUK BAHAN KAPUR Kapor Hidroksida: Kapur Tembok Kemurniannya: 95 - 96% Pembuatannya: CaO + MgO + H 2 O Ca(OH)2 + Mg(OH) 2 Reaksinya di udara lembab terbuka: Ca(OH)2 + CO2 CaCO 3 + H2O Mg(OH)2 + CO2 NgCO 3 + H2O Reaksinya dlm tanah: MISEL - H + Ca(OH) 2 MISEL - Ca + 2H2O Ca(OH)2 + 2 H 2 CO 3 Ca(HCO 3 ) 2 + 2 H2O % Oksida CaO : 60% Ekuivalen oksida Ca: 76.7 Daya netralisasi : 136.9 (kesetaraan CaCO 3 ) Persentase unsur Ca: 42.8 % Oksida MgO : 12% Persentase unsur Mg: 7.2

35 35 BENTUK BAHAN KAPUR Kapor Karbonat : Kapur Kalsit = CaCO3 Kapur Dolomitik = CaMg(CO3)2 Dolomit= MgCO3 Kemurniannya : 75 - 99% Pembuatannya: Batuan CaCO3 digiling Kapur giling Reaksinya dlm tanah: MISEL -H + CaCO 3 MISEL -Ca + H2O + CO 2 Oksida CaO = 44.8%; MgO = 6.70% Ekuivalen oksida Ca : 54.10 Daya netralisasi : 96.6 (kesetaraan CaCO 3 ) Persentase unsur Ca = 32; Mg = 4.03 Karbonat: CaCO3 = 80%; MgCO3 = 14% Total = 94%

36 36 PENGARUH KAPUR PADA TANAH Pengaruh Fisik: - Membantu granulasi - agregasi - Memperbaiki struktur tanah - Tata Udara (Aerasi) - Tata Air / Pergerakan air Pengaruh Kimia: (Bila tanah dg pH= 5.0 dikapur hingga ph naik menajdi 6.0) - Kepekatan kation hidrohen menurun - Kepekatan anion hidroksil meningkat/ naik - Daya larut Fe, Mn dan Al akan menurun - Ketersediaan fosfat dan Mo akan diperbaiki - Ca dd dan Mg dd akan naik - Persentase kejenuhan basa (KB) akan naik - Ketersediaan kalium berubah tgt keadaan. Pengaruh Biologik: - Merangsang kegiatan jasad tanah, termasuk mikroba tanah - Membantu pembentukan humus - Aminisasi, amonifikasi, oksidasi belerang dipercepat - Fiksasi nitrogen dari udara secara biologis dirangsang - Nitrifikasi dipercepat

37 37 JENIS TANAMAN yg SESUAI TANAH MASAM dg KEBUTUHAN KAPUR MINIMUM Kebutuhan Kejenuhan pHVarietas tnm yg toleran kapurAl (t/ha)(%) 0.25 - 0.5 68 - 75 4.5 - 4.7 Gogo, ubikayu, mangga, mente Jeruk, Nanas, Desmodium, Cen- trosema, Paspalum 0.5 - 1.0 45 - 58 4.7 - 5.0Cowpea, Plantain 1.0 - 2.0 31 - 45 5.0-5.3 Jagung, Black bean Sumber: Spain et al. 1975

38 38 MEKANISME TOLERANSI / KEPEKAAN TANAMAN thd Al dlm TANAH 1. Morfologi akar. Varietas yg toleran Al mampu menumbuhkan dan tidak mengalami kerusakan ujung-ujung akar pd kondisi tanah masam kaya Al 2.Perubahan pH rhizosfer. Varietas yg toleran Al mampu menaikkan pH zone rhizosfernya, sdg varietas yg peka menurunkan pH tsb. Perubahan pH ini diduga akibat dari penyerapan anion diferensial-selektif, sekresi asam organik, CO 2 dan HCO 3 -. 3.Lambatnya translokasi Al ke tajuk. Varietas yg toleran Al mengakumulasikan Al dlm akar, dan mentranslokasikan ke tajuk secara lebih lambat dp jenis yg peka.

39 39 MEKANISME TOLERANSI / KEPEKAAN TANAMAN thd Al dlm TANAH 4. Al dalam akar tidak menghambat penyerapan dan translokasi Ca, Mg dan K dlm varietas yg toleran Al. 5. Toleransi varietas kedelai thd Al berhubungan dengan penyerapan dan translokasi Ca. 6. Toleransi varietas keNTANG thd Al berhubungan dengan translokasi Mg dan K. 7.Toleransi varietas padi thd Al berhubungan dengan tingginya kandungan Si dlm tanaman. 8.Varietas yg toleran Al tidak mengalami hambatan penyerapan dan translokasi fosfat; tdk dmk varietas yg peka.

40 40 1. Tujuan utama pengapuran adalah menetralisir Al dd, dan biasanya diikuti oleh kenaikan pH hingga 5.5. 2.Kalau diduga ada keracunan Mn, maka pH dinaikkan 6.0 3. Faktor-faktor yg harus diperhatikan: 1. Jml bahan kapur yg diperlukan untuk menetralkan Al dd hingga tingkat yg sesuai bagi tanaman 2. Kualitas bahan kapur 3. Cara penempatan / aplikasi bahan kapur ke tanah.

41 41 RESPON TANAMAN thd PENGAPURAN Umumnya pertumbuhan tanaman menjadi lebih baik. Tnm kacang-kacangan menyukai kapur, termasuk kedelai dan kacang tanah Alasan terjadinya respon tanaman: 1. Pengaruh langsung unsur hara Ca dan Mg 2. Dinetralkannya senyawa-senyawa toksik 3. Penekanan gangguan penyakit tanaman 4. Ketersediaan beberapa unsur hara meningkat 5. Rangsangan kegiatan jasad mikro akan meningkatkan ketersediaan hara 6. Beberapa tanaman tertentu tidak senang pengapuran, misalnya semangka. 7. ……. Dll.

42 42 1. Kamprath (1970): Dosis kapur = 1.5 x ( me Al dd topsoil) = m.e. Ca yg harus diaplikasikan sbg kapur 2. Dosis kapur yg dihitung dg cara ini mampu menetralkan 85 - 90 % Al dd dlm tanah yg mengandung 2 - 7% bahan organik 3.Faktor 1.5 digunakan untuk menetralkan H+ yg dilepaskan oleh bahan organik atau hidroksida Fe dan Al kalau pH tanah meningkat 4.Dalam tanah yg kaya bahan organik, faktor tersebut menjadi 2.0 atau 3.0, karena adanya H dd. 5.Untuk setiap satu m.eq. Al dd dlm tanah diperlukan aplikasi 1.5 meq Ca atau setara dg 1.65 ton CaCO3 per ha. 6.Faktor penting lain adalah kandungan Al dd dlm tanah yang dapat ditolerir oleh tanaman tertentu 7.Jagung sensitif terhadap kejenuhan Al 40-60%. Pengapuran hingga kejenuhan Al = 0% dapat menguntungkan, namun pengapuran untuk menurunkan kejenuhan Al menjadi 20% dapat lebih ekonomis.

43 43 RESPON HASIL TERHADAP PENGAPURAN 10 20 30 40 50 60 70 80 90 100 % kejenuhan Al % Hasil maks. 100 80 60 40 20 00 Sumber: Abruna et al. 1975 Oxisols & Ultisols Sumber: Abruna et al. 1975 Oxisols & Ultisols Rumput gajah Sorghum Jagung

44 44 1. Kapur biasanya dibenamkan sedalam 15 cm beberapa hari sebelum tanam. 2.Tanah Oksisol sangat masam yg topsoilnya telah dikapur hingga pH 5.5, sebagian besar akar jagung tumbuh dalam topsoil. Tingginya kandungan Al dd dalam subsoil mencegah pertumbuhan akar lebih dalam. 3.Penempatan kapur pada lapisan tanah yg lebih dalam mengakibatkan perakaran tanaman tumbuh lebih dalam dan hasil tanaman lebih baik 4.Deep placement kapur dimungkinkan pada tanah-tanah berpasir yang strukturnya baik. 5.

45 45 PENGAPURAN & HASIL JAGUNG 1 2 3 4 5 6 7 Dosis kapur ( ton/ha) Hasil biji, t/ha 654321654321 Sumber: Gonzales, 1973 Tanah Oxisols Zone pengapuran 0-30 cm Zone pengapuran 0-15 cm

46 46 1. Efek residu pengapuran tergantung pada seberapa cepat Ca dan Mg digantukan oleh residu kemasaman dari pupuk nitrogen. 2.Pada tanah Hydrandept Selama lima tahun sejak aplikasi 2 ton kapur/ha ternyata nilai Al dd dalam tanah dipertahankan sekitar 1 meq, semula sebesar 3 m.eq, meskipun sebagian besar Ca++ telah tercuci. Setelah lima tahun efek residu pengapuran lenyap. 3.Pada Oxisol berpasir. Jagung dan kedelai respon positif terhadap kapur enam tahun setelah aplikasi, respon hasil meningkat dg waktu, diduga karena pelarutan partikel kasar kapur.

47 47 KELEBIHAN Pemberian KAPUR Kelebihan: penambahan kapur yg mengakibatkan meningkatan pH tanah melebihi yang diperlukan untuk pertumbuhan optimum tanaman. Tanaman akan menderita, terutama pada tahun pertama aplikasi kapur Biasanya terjadi pada tanah berpasir / berdebu yg miskin bahan organik Pengaruh buruk pengapuran yg berlebihan: 1. Kekurangan Fe, Mn, Cu dan Zn 2. Ketersediaan fosfat mungkin menurun karena pembentukkan senyawa kompleks dan tidak larut 3. Serapan fosfat dan penggunaannya dlm metabolisme tanaman dapat terganggu 4. Serapan B dan penggunaannya dapat etrganggu 5.Perubahan pH yang terlalu melonjak dapat berpengaruh buruk 6. ………dst. 7. ……. Dll.

48 48 Apakah KAPUR perlu diberikan? Penggunaan kapur harus didasarkan pada : Kemasaman Tanah dan Kebutuhan Tanaman 1. Sebelum mengapur tanah, karakteristik kimia tanah perlu diteliti 2. pH tanah dan Kejenuhan Basa harus ditentukan secara akurat : Lapisan atas dan Lapisan bawah 3. Cara lain adalah menentukan Al dd 4. ………. 1. Kebutuhan kapur untuk tanaman secara umum atau untuk tanaman tertentu 2. Pengelompokkan respon tanaman thd kapur : - Tanaman Senang Pengapuran - Tanaman tidak senang Pengapuran - Tanaman netral

49 49 Bentuk KAPUR yg dipakai Lima faktor unt menentukan bentuk kapur : 1. Jaminan mutu kimia bahan kapur 2. Harga bahan 3. Kecepatan reaksi dengan tanah 4. Kehalusan bahan kapur 5. Hal lain-lain (penyimpangan, pembungkusan dsb. Kecepatan Reaksi: 1. Kapur kaustik (kapur tohor dan tembok) lebih cepat bereaksi dg tanah dp kapur giling 2. Kapur dolomitik bereaksi lebih lambat dp kapur kalsitik 3. Bentuk tepung halus lebih cepat bereaksi dg tanah 4. …. Dll. Pertimbangan biaya: 1. Harga bahan kapur 2. Biaya angkut ke lahan usaha 3. Biaya aplikasi bahan kapur ke lahan usaha 4. ….. dll

50 50 Jumlah KAPUR yg diaplikasikan Enam faktor penting unt menentukan jumlah kapur : 1. Karakteristik tanah: Lapisan atas: pH, Al dd, Tekstur & Struktur, BOT Lapisan bawah: pH, Al dd, Tekstur & Struktur 2. Tanaman yg akan ditanam 3. Lamanya pergiliran tanaman 4. Macam bahan kapur dan komposisi kimianya 5. Kehalusan bahan kapur 6. Pengalaman praktis Karakteristik Tanah : 1. Tekstur dan BOT menentukan besarnya kapasitas jerapan 2. Semakin tinggi Kapasitas jerapan dan Al dd, semakin banyak kapur diperlukan 3. Kemasaman dan Al dd tanah lapisan bawah ikut menentukan jumlah kapur Contoh: Jml kapur giling unt tanah mineral setebal 20 cm seluas 1 ha: Untuk menapai pHJumlah kapur, ton/ha 5.21.2 x me Al dd 5.51.5 6.02.1

51 51 Teknologi Aplikasi KAPUR Cara Aplikasi : 1.Kapur disebar di permukaan tanah yg baru dibajak, kemudian dicampur rata dengan tanah olahan 2.Kapur disebar di permukaan tanah, tanah dibajak (diolah) dan dicampur rata Waktu Aplikasi : 1. Biasanya sebelum tanam 2.Kapur diberikan bila diperkirakan tidak turun hujan pd saat aplikasi 3. …… 1. Pertanaman tunggal 2. Pertanaman majemuk: Pola pergiliran tanaman Kapur diberikan pd tanaman yg paling memerlukan pengapuran

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