Bahan Kajian MK. Dasar Ilmu Tanah KEMASAMAN TANAH pH Tanah smno.jurtnh.fpub.nop2013

pH = - log (H+ ion concentration) neutral As pH increases… As pH decreases… Sumber: Brady and Weil, 2002

Kisaran pH optimum untuk berbagai jenis tanaman

Mo lebih tersedia kalau pH naik ^ http://www.farmtested.com/research_pp.html

Aluminum toxicity is minimal above Toksisitas Aluminum Toxic forms of Al are bioavailable at low pHs Aluminum toxicity is minimal above pH 5.5 http://www2.ctahr.hawaii.edu/tpss/research_extension/rxsoil/alroot.gif

Bentuk-bentuk Kemasaman Tanah pH tanah mengukur kemasaman aktif Kemasaman Cadangan Brady and Weil, 2002

ΔpH Kemasaman Cadangan Tanah dengan KTK tinggi Tanah dengan KTK rendah Kemasaman cadangan mensuplai kemasaman aktif Very little lime is needed to neutralize the active acidity in soils ΔpH ΔpH Reserve acidity Active acidity Reserve acidity Active acidity Tanah dengan KTK tinggi Tanah dengan KTK rendah

- - - - - - - - - - - - + + K+ Ca+2 Mg+2 H+ Al+3 K+ SO4-2 Ca+2 Setiap muatan yang ditandai pada diagram ini mencerminkan 1 centimol muatan per kg tanah K+ - - Ca+2 - - Mg+2 - - H+ Humus H20 H20 H20 exchangeable cations Exchangeable acidity soil solution H20 H20 H20 - Clay - - Al+3 + H2O ↔ Al(OH)3 + 3H+ - + - + - K+ SO4-2 Ca+2 Apakah Kejenuhan Basa ?

Apakah pH berhubungan dengan kejenuhan basa? 100 80 60 40 20 0 Acid Saturation, %

Muatan yang tergantung pH The dominant clay minerals in IL have mostly permanent charge

Muatan listrik pada substansi humik (dan liat yg aktivitasnya rendah) sangat tergantung pH Muatan tergantung pH Ion H+ berdisosiasi kalau pH tanah naik dan re-asosiasi kalau pH turun. Brady and Weil (2002)

Soil acidity increases when H+ producing processes exceed H+ consuming processes.

Banyak proses yang menambah ion H+ ke tanah 1) Carbonic acid forms when carbon dioxide dissolves in water. H+ ions are released when carbonic acid dissociates: H2CO3 → HCO3- + H+ 2) Organic acids form during the decomposition of organic matter. H+ ions are released when these organic acids dissociate. 3) Sulfuric and nitric acids form during the oxidation of reduced forms of N and S (e.g., NH4+ from fertilizer, elemental S). NH4+ + O2 → NO3- + 2H+ S0 + O2 → SO4-2 + 2H+ 4) Sulfuric and nitric acids form when sulfur oxides and nitric oxides (released into the atmosphere by automobile emissions, industry smoke stacks, volcanoes, forest fires) dissolve in precipitation. H2SO4 and HNO3 are strong acids and fully dissociate in water. 5) Roots release H+ to balance internal charge when cation uptake exceeds anion uptake. VERY IMPORTANT PART OF SOIL FORMATION

Banyak proses yang mengkonsumsi ion H+ dalam tanah (1) Weathering of most minerals (e.g., silicates, carbonates…) (2) Decomposition of organic anions (3) Reduction of oxidized forms of N, S and Fe. (4) Roots release OH- or HCO3- to balance internal charge when anion uptake exceeds cation uptake (5) Inner sphere adsorption of anions (especially sulfate) which displaces hydroxyl (OH-) groups

Oksida-oksida C, N dan S menyebabkan hujan asam Brady and Weil, 2002

Sumber-sumber penyangga pH dalam tanah Chadwick and Chorover ( 2001) Carbonates Chadwick and Chorover ( 2001)

K+ H+ pH rizosfir tanaman berubah kalau mengatur keseimbangan muatan listrik internalnya. NO3- ?

Mana tanaman yang dipupuk nitrat? Mana tanaman yang dipupuk ammonium ? http://departments.agri.huji.ac.il/plantscience/topics_irrigation/uzifert/4thmeet.htm

Masukan asam mendorong pencucian kation basa Mengapa pencucian kation basa memicu kemasaman tanah ? Brady and Weil, 2002

Siklus N NH3 1H+ consumed released into the soil 2 H+ yang dihasilkan selama proses nitrifikasi diimbangi dengan 2 H+ yang dikondumsi selama pembentukan NH4+ dan serapan NO3- oleh tanaman

Monoammonium phosphate Standard jumlah kapur yg diperlukan untuk menetralkan kemasmaan yang dihasilkan oleh pupuk N. Asumsi: 1) Semua ammonium-N dikonversi menjadi nitrate-N 2) separuh nitrate tercuci. Sumber Nitrogen Komposisi Kebutuhan Kapur (lb CaCO3 / lb N) Anhydrous ammonia 82-0-0 1.8 Urea 46-0-0 Ammonium nitrate 34-0-0 Ammonium sulfate 21-0-0-24 5.4 Monoammonium phosphate 10-52-0 Diammonium phosphate 18-46-0 3.6

Ratio Kation : N dalam biomasa tanaman Panen biomasa tanaman berarti mengambil sejumlah alkalinitas dari lahan pertanian Tanaman Ratio Kation : N dalam biomasa tanaman Kapur yg diperlukan untuk menggantikan alkalinitas yang diambil dalam panen tanaman (lb CaCO3 /100 lb N yang dipanen) Corn grain 0.14 25 Corn stover 0.73 131 Soybean Oats grain Oats straw 0.94 169 Alfalfa 1.41 254 http://www.ianrpubs.unl.edu/epublic/pages/publicationD.jsp?publicationId=111

Lime rates should be guided by soil testing

Sumber variasi dalam pengukuran pH tanah 1. The soil to solution ratio used when measuring pH. 2. The salt content of the diluting solution used to achieve the desired soil to solution ratio. 3. The carbon dioxide content of the soil and solution. 4. Errors associated with standardization of the instrument used to measure pH.

Mengapa mengukur pH tanah dengan menggunakan larutan garam? Water pH > Salt pH Brady and Weil, 2002

pH tanah tergantung pada metode pengukurnanya. As a result, the method of measurement should be reported whenever soil pH data is discussed.

When a soil is limed, Ca+2 from the lime displaces exchangeable acidity from the soil colloids. The active acidity that is generated reacts with the carbonate ions from the lime, producing water and carbon dioxide. H+ Ca+2 soil colloid + CaCO3 soil colloid + H2O + CO2 H+

“Illinois method” untuk menentukan kebutuhan kapur How do you know which line to use ? http://iah.aces.uiuc.edu/pdf/Agronomy_HB/11chapter.pdf

Memilih bahan kapur yang tepat Light colored (< 2.5% OM) Line A: Dark colored silty clays and silty clay loams (CEC > 24) Line B: Light and medium colored silty clays and silty clay loams, dark colored silts and clay loams (CEC 15-24) Line C: Light and medium colored silt and clay loams, dark and medium colored loams, dark colored sandy loams (CEC 8-15) Line D: Light colored loams, light and medium colored sandy loams and all sands (CEC < 8) Line E: Mucks and peat (organic soils). Light colored (< 2.5% OM) Medium colored (2.5-4.5% OM) Dark colored (4.5% OM)

Tidak semua batu-kapur sama kualitasnya ! Pure calcium carbonate has a calcium carbonate equivalency (CCE) of 100 and is the standard against which all liming materials are compared. A ton of material with a CCE of 90 % can neutralize 10% less acid than a ton of pure calcium carbonate. Liming materials that are finely ground, have more surface area in contact with the soil solution than coarser ground materials and thus will neutralize soil acidity more rapidly. Fineness of grind is rated according to the percentage of material that will pass through 8-, 30-, and 60-mesh screens.

Reaksi kapur dalam tanah memerlukan waktu

pH tanah dan Kebutuhan Kapur dapat beragam dalam suatu bentang lahan pH measurements on the fly

Barak P, Jobe BO, Krueger AR, Peterson LA, Laird DA 1997 Barak P, Jobe BO, Krueger AR, Peterson LA, Laird DA 1997. Effects of long-term soil acidification due to nitrogen fertilizer inputs in Wisconsin. PLANT AND SOIL. 197(1): 61-69 Agroecosystems are domesticated ecosystems intermediate between natural ecosystems and fabricated ecosystems, and occupy nearly one-third of the land areas of the earth. Chemical perturbations as a result of human activity are particularly likely in agroecosystems because of the intensity of that activity, which include nutrient inputs intended to supplement native nutrient pools and to support greater biomass production and removal. At a long-term fertility trial in South-Central Wisconsin, USA, application of ammoniacal N fertilizer resulted in significant increases in exchangeable acidity accompanied by decreases in cation exchange capacity (CEC), base saturation, and exchangeable Ca2+ and Mg2+ . Plant analysis shows that a considerable portion of the alkalinity generated by assimilation of N (and to a lesser extent by S) is sequestered in the above-ground plant parts as organic anions and is not returned to the soil if harvested. Elemental analysis of soil clays indicates a loss of 16% of the CEC. The reversibility of this change is doubtful if the changes are due to weathering of soil minerals.

Permasalahan kesuburan tanah pada kondisi pH tanah yang ekstrim Toksisitas Al pada akar tanaman Fe deficiency Toksisitas Mn pada akar tanaman Mn deficiency Defisiensi Ca dan Mg Zn deficiency Defisiensi Mo pada legumes *Osmotic stress from salts P terikat kuat oleh Fe dan Al P tied up by Ca and Mg Transformasi N lambat Potato scab