Soil Chemical Properties PDF

Soil chemical properties * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 1 Learning objectives: Determine and understand the different chemical properties of soil. Describe the process of cation exchange. Discuss the importance of soil pH, ion exchange, buffering capaci...

Soil chemical properties * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 1 Learning objectives: Determine and understand the different chemical properties of soil. Describe the process of cation exchange. Discuss the importance of soil pH, ion exchange, buffering capacity, salinity, and soil colloids on nutrient availability. Discuss the different management strategies for acid and salt affected soils. 2 Soil chemical properties ❏ The ability of soil to provide the essential elements needed for plant growth. * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 3 Soil chemical properties 1. Soil colloids a. Organic colloids b. Inorganic colloids 2. Exchange capacity a. Cation exchange capacity b. Anion exchange capacity 3. Base saturation 4. Soil pH 5. Macro and micronutrients 6. Soil salinity and sodicity * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 4 Exchange capacity ❑ is the soils' ability to retain and supply nutrients to a crop a. Cation exchange capacity b. Anion exchange capacity * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 5 Cation exchange capacity ❑ the ability or capacity of a soil colloid to sorb or hold cations. Anion exchange capacity ❑ refers to the ability or capacity of a soil colloid to sorb or hold anions such as HCO3- , Cl- , NO3- * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 6 * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 7 Soils with high CEC have low leaching potential Soil with Soil with low CEC high CEC * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 8 * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 9 Exchangeable cations (on soil Soluble cations (in solution) can be surfaces) cannot be removed by removed by leaching. leaching. * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 10 Cation exchange capacity ❑ often expressed in cmolc /kg or milliequivalent /100g (older unit) ❑ 1 milliequivalent is equal to 6 x 1020 negative charges Therefore, a soil with CEC of 1 meq/100 g means that there are 6 x 1020 negative charges on 100 g soil * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 11  Atomic weight Equivalent weight of cation (g/equivalent)= ------------------------------ (+) valence Equivalent wt of cation Weight of 1 m.e. cation (g/meq) = ------------------------------- 1000 Weight of cation present CEC (meq/100g)= ------------------------------- Weight of 1 m.e. cation * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 12 Problem 1: if a soil had a CEC of 1 meq/100 g. How much (grams) Na this soil can hold? a. Compute equivalent wt. of Na= 23/1 = 23 g/equivalent a. Compute the meq wt. of Na= 23/1000 = 0.023 g/meq a. Compute the wt. of cation = 1 meq/100 g soil x 0.023 g/meq= 0.023 g Na/ 100 g soil * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 13 * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 14 * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 15 Problem 2: If a soil had a CEC of 20 meq/100 g. How many milligrams of Ca2+ will this equal? a. Compute equivalent wt. of Ca= 40/2 = 20 g/equivalent a. Compute the meq wt. of Ca= 20/1000 = 0.02 g/meq c. Compute the wt. of cation = 20 meq/100 g soil x 0.02 g/meq= 0.4 g Ca/ 100 g soil or 400 mg Ca/100 g soil * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 16 Problem 3: A 100-g soil sample was found to contain 0.21 g Ca2+. Calculate the CEC of the soil. a. Compute equivalent wt. of Ca= 40/2 = 20 g/equivalent a. Compute the meq wt. of Ca= 20/1000 = 0.02 g/meq c. CEC= 0.21 g Ca2+/0.02 g/meq=10.5 meq/100 g soil * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 17  Atomic weight Equivalent weight of cation (g/equivalent)= ------------------------------ (+) valence Equivalent wt of cation Weight of 1 m.e. cation (g/meq) = ------------------------------- 1000 Weight of cation present CEC (meq/100g)= ------------------------------- Weight of 1 m.e. cation * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 18 Problem 4: A soil test shows it contains 0.972 meq/100 g of potassium, 1.11 meq/100g of magnesium, 8.0 meq/100g calcium and 0.10 meq/100g sodium. Calculate the CEC of the soil CEC =Base cations + acid cations CEC= (Ca2+ + Mg2+ + K+ + Na+) + (H+ + Al3+ + NH4+) CEC =0.972 + 1.11 + 8.0 + 0.10 = 10.2 meq/100 g * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 19 Problem 5: A soil test shows it contains 0.972 meq/100 g of potassium, 1.11 meq/100g of magnesium, 8.0 meq/100g calcium, 0.10 meq/100g sodium and 4.8 meq/100 g H+. Calculate the CEC of the soil CEC =0.972 + 1.11 + 8.0 + 0.10 + 4.8= 15 meq/100 g * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 20 Problem 6: A soil test shows it contains 0.972 meq/100 g of potassium, 1.11 meq/100g of magnesium, 8.0 meq/100g calcium, 0.10 meq/100g sodium, 4.8 meq/100 g H+ and 3.5 meq/100 g Cl-. Calculate the CEC of the soil CEC =0.972 + 1.11 + 8.0 + 0.10 + 4.8= 15 meq/100 g * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 21 Which do you think has higher soil CEC? a. Sandy soil b. Clayey soil * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 22 * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 23 * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 24 CEC & Soil type Rating CEC (me/100g) Comment Low 5-12 Low organic matter. Sandy soil Medium 12-25 Pumice soil, Lower fertility High 25-40 High fertility soil, High clay content. Very High 40+ Peat soils * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 25  CEC VS Grain Composition From Horowitz, 1991 * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 26 CEC and pH in Soil Orders * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 27 Relationship between CEC to pH * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 28 Factors affecting the strength of cation adsorption on the surface of clay 1. Ion concentration in the soil solution (law of mass) 2. Valences ❑ the strength of cation adsorption increases as the charge of the cation increases Al3+ >Ca2+ >Mg2+ > K+ > Na+ * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 29 Factors affecting the strength of cation adsorption on the surface of clay 3. Radii ❑ smaller radii/radius of cation is highly attracted to clay surfaces 4. Hydration properties ❑ adsorption of cation increases as cation becomes less hydrated Rb+ > K+ > Na+ > Li+ * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 30 31  Calcium is more abundant in the clay surfaces than sodium * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 32  Order of the strength of adsorption of cations! Strong --------------------------------------Weak Al+3 > H+ > Ca+2 > Mg+2 > [K+ = NH4+ ] > Na+ This is called the lyotropic series The smaller the hydrated radius and the greater the valence, the higher the strength of adsorption * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 33  Rules of ion exchange 1. Rapid 2. Process is Reversible 4. Charge by charge basis 3. Ratio Law: ❑ ratio of exchangeable cations will be same as ratio of solution cations * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 34 Examples of cation exchange K+ Ca2+ Ca2+ K+ K+ K+ K+ K+ K+ K+ K+ Al3+ K+ Al3+ The interchange between a cation in solution and one on a colloid must be CHARGE balanced. The reactions are reversible * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 35 Add K fertilizer… K+ Ca+2 K+ Ca+2 Ca+2 + K+ + K+ K+ Ca+2 K+ K+ K+ 1 Ca : 2 K 1 Ca : 2 K Same ratio * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 36 The amount of cations a soil can hold is dependent on: 1. Type of clay that is present 2. The amount of clay 3. The amount of organic matter present 4. pH of soil * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 37  CEC of clay minerals Type Mineral Layer CEC Comment Specific charge surface (mg2 /g) 1:1 kaolinite 0 2-15 Low layer charge; low 7-30 CEC 2:1 Mica (illite) 0.7-1.0 10-40 High layer charge; low 40-100 CEC due to fixed K+ Vermiculite 0.6-0.9 100-200 CEC proportional to layer 600-800 charge Montmorillonite 0.2-0.6 70-120 CEC proportional to layer 600-800 charge 2:1:1 Cholorite Variable 10-40 CEC less due to 25-150 interlayer filling * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 38 * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 39 What does a high CEC mean? 1. Soil can sorb/retain large amount of cations 2. Soil has more cations reserve 3. Effective in fixing contaminants * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 40 * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 41  Base saturation ❑ The proportion of the CEC occupied by basic (+) nutrients such as Ca, Mg, K, Na Two adsorbed ions: a. Acidic or acid-forming cations -H+ , Al3+ , Fe2+ b. Basic or alkaline-forming cations - Ca2+ , Mg2+ , K+ , Na+ * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 42  Base saturation formula exchangeable bases (meq/100g) % Base saturation= ------------------------------------------------ x 100 CEC (meq/100 g) * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 43 Problem 1: For a soil with 0.5 meq of K, 2.1 meq of Ca, 0.4 meq of Mg and a CEC of 4.0 meq/100g. Calculate the base saturation Base saturation= (meq bases/ CEC) x 100 Base saturation= (0.5 meq K+ 2.1 meq Ca + 0.4 meq Mg)/4.0 meq CEC x 100 = (3.0/4.0 ) x 100 Base saturation = 75 % Note: A relatively high base saturation of CEC (70-80% should be maintained for most cropping systems * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 44 Problem 2: A soil was found to have 9.4 meq/100 g of H+ , 14 meq/100 g Ca2+ , 3 meq/100 g Mg2+ , 0.5 meq/100 g K+ , 0.1 meq/100 g Na+. Compute the CEC and Base saturation of the soil CEC= 9.4 + 14 + 3 + 0.5 + 0.1 CEC= 27 meq/100 g Base saturation= (17.6/27) x 100 Base saturation= 65 % * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 45 Problem 3: A soil with CEC of 10 meq/100g has 6 meq/100g of bases (Ca, Mg, K, Na) occupying exchange sites. What is the percent base saturation of the soil? Base saturation= (6 meq/10 meq) x 100 Base saturation= 60 % * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 46 What does a high % base saturation mean? 1. Bases dominate the exchange site (soil surfaces) 2. Soil is not acidic 3. Soil has high buffering capacity * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 47 Soil pH ❑ measure the hydrogen concentration in soil solution ❑ measure soil acidity or alkalinity ❑ Negative logarithm or -log [H+ ] concentration in soil solution * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 48 * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 49  [H+] pH (moles/L) 0.001 3 0.0001 4 0.00001 5 0.000001 6 0.0000001 7 ❑ A soil with a pH 3 ha 10 times more H+ compared to soil with a pH of 4 ❑ A soil with pH 3 has 100 times more H+ compared to soil with a pH of 4 * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 50  pH Remarks 4.00-4.49 Extremely acidic 4.50-4.99 Very strongly acidic 5.00-5.49 Strongly acidic 5.50-5.99 Moderately acidic 6.00-6.49 Slightly acidic 6.50-6.99 Very slightly acidic 7.00-7.99 Slightly alkaline 8.00-8.49 Moderately alkaline 8.50-9.49 Strongly alkaline 9.50-10.00 Very strongly alkaline Based on: London, J. R. 1991. Booker Tropical 1 Soil Manual * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 51 * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 52 Importance of knowing soil pH 1. Major determinant of nutrient availability ❑ example: P is usually not in plant available forms at pH of 8.0 ❑ pH below 5.0 plant suffers H, Al and Mn toxicity and K, Ca, Mg deficiency * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 53 * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 54 * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 55 * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 56  pH affects soil nutrient availability 1. Alkaline (pH > 7.0) 2. Acidic (pH < 7.0) 3. Neutral (pH = 7.0 * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 57 * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 58 * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 59 * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 60 * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 61  Importance of knowing soil pH 2. May have direct influence on the growth of crops ❑ At low pH, Al+ concentration maybe very high and could cause injury to plants. ❑ In strongly acidic soils, plant may suffer from aluminum, Fe, Mn toxicities ❑ At high pH plant suffers from Mn and Fe deficiency and toxicity of B and Na * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 62 Importance of knowing soil pH 3. Influences microbial activity ❑ activity of bacteria is adversely affected at low pH ❑ low microbial activity (nitrification, N fixation) * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 63 Types of acidity 1. Active acidity- H+ and Al3+ in the soil solution 2. Exchangeable acidity-portion of H+ and Al3+ ions that are adsorbed by soil colloids(e.g., clay and organic matter) that can be replaced by salt solution such as KCl or NaCl. 3. Residual acidity - refers to bound H+ and Al3+ ions that cannot be replaced by salt solution. 4. Potential acidity-sulfur oxidation in acid sulfate soil * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 64 Causes of soil acidity 1. Acid parent materials ❑ soils that developed from weathered granite are likely to be more acidic than those developed from shale or limestone 2. Leaching of basic cations due to high rainfall ❑ the higher the average annual rainfall the more leaching. Basic cations are removed more easily than H+ and Al3+ * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 65 Acidifying a Soil * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 66 Causes of soil acidity 3. Organic matter decomposition CO2 + H2O = H2CO3 (carbonic acid) H2 CO3 = HCO3- + H+ * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 67 Causes of soil acidity 4. Fertilizer containing NH4 NH4+ + 2O2 = H2O + H+ + H + + NO3- Conversion of NH4+ (ammonium) to NO3- (nitrate) * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 68 Causes of soil acidity 5. Al hydrolysis Al3+ + H2O Al(OH)2+ + H+ Al (OH)2+ + H2O Al(OH)+ 2 + H+ Al(OH)+ 2 + H+ Al(OH)3 + H+ * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 69 6. Crop removal Root interior Soil solution Example 1 NH4+ Uptake of cations balanced by H+ release of H+ ions from root Ca2+ acidifying effect Example 2 2H+ Ca2+ Uptake of cations balanced by Example 3 uptake of anions SO42- no effect on pH NO3- Uptake of anions balanced by Example 4 release of bicarbonate HCO3- alkalinizing effect * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 70  NO3- Uptake of anions balanced by Example 4 release of bicarbonate HCO3- alkalinizing effect - The increased concentration of HCO3- ions tends to reverse the dissociation of carbonic acid thereby consuming H+ ions and raising the pH of the soil solution H2 CO3 HCO3- + H+ Carbonic acid * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 71 Causes of soil acidity 8. Acids precipitation- rain, snow, fog, dust a. carbonic acid b. sulfuric acid c. nitric acid H2 SO4 SO42- + 2 H+ Sulfuric acid HNO3 NO3- + H+ Nitric acid * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 72  Acid Rain * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 73 How to manage soil acidity 1. Apply lime CaCO3 + H2O Ca2+ + HCO3- + OH- OH- + H+ H2O ❑ lime reduces the concentration of H+ ions and increases the concentration of OH- ions and adds non acid forming cations * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 74 Calcium carbonate * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 75 The common liming materials Material Composition CCE (%) Calcium carbonate CaCO3 (pure) 100 Calcitic limestone CaCO3 80-100 Dolomitic limestone CaCO3. Mg CO3 95-108 Quick lime CaO (calcium oxide) 150-175 Hydrated or slaked lime Ca (OH)2 120-135 Marl CaCO3 70-90 Ground oyster shells CaCO3 90-100 Wood ashes Ca, Mg, and K oxides 40-50 * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 76 Approximate amount of finely ground limestone needed to raise the pH of a 7-inch layer of soil Lime requirements (tons per hectare) Soil texture From pH 4.5 to 5.5 From pH 5.5 to 6.5 Sand & loamy sand 0.5 0.6 Sandy loam 0.8 1.3 loam 1.2 1.7 Silt loam 1.5 2.0 Clay loam 1.9 2.3 Muck 3.8 4.3 * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 77 Factors influencing the quality of liming materials 1. Purity ❑ any impurities in the lime will reduce its ability to neutralize acidity (sand, rock, clay) 2. Fineness ❑ large particles react more slowly and less completely than fine particles * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 78  Some important crop species that can tolerate to soil acidity in the tropics: 1. Annual crop species ❑ rice, peanut, cowpea, potato, cassava, pigeon pea, millet, kudzu, crotolaria 2. Pasture species ❑ brachiaria, andropogon, panicum, digitaria, napier grass, centrosema, stylosanthes 3. Plantation crops ❑ banana, oil palm, rubber, coconut, cashewnut, coffee, guarana, tea, leucaena, eucalyptus, papaya, pine apple * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 79 How to manage acid soil 3. Gypsum 4. Application of organic matter 5. Wood ashes * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 80 Salt-Affected soils 1. Saline soil or white alkali soil ❑ contains a high amount of soluble salts, primarily calcium (Ca2+) , magnesium (Mg2+) and potassium (K+) 2. Sodic soil or black alkali soil ❑ soils dominated by sodium (Na2+) 3. saline-sodic soil ❑ soils have both high salts and Na+ content * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 81 What are salts? ❑ Salts is a water-soluble compound that, in soil, may include calcium (Ca2+) , magnesium (Mg2+), sodium (Na+) and potassium (K+), chloride (Cl- ), bicarbonate (HCO3- ) or sulfate (SO42- ) * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 82 * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 83 * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 84 Effects of high salt in plants * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 85 Effects of high salt in plants * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 86 * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 87 * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 88 * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 89 Classification of salt affected soils based on some characteristics classification EC Soil pH Exchangeable Na Soil physical mmhos/cm condition Saline >4.0 4.0 15 Normal (flocculated) * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 90 Salinity levels ❑ 0-2 mmhos/cm = tolerable/less saline ❑ 2-4 mmhos/cm = moderate saline ❑ 4-8 mmhos/cm =highly saline ❑ 8-16 mmhos/cm =excessive ❑ >16 mmhos/cm =very excessive * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 91 How do salts accumulate in soil 1. Weathering of primary minerals or be deposited by wind or water that carries salts from other locations 2. Evaporation exceeds precipitation 3. Irrigation containing high levels of soluble salts 4. Application of fertilizer, amendment and manure * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 92 Effects of high salt concentration 1. Excess salts in the root zone reduce the amount of water available to plants and can cause the plant to expend more energy to exclude salts and take up pure water 2. High salinity causes water in the plants to be pulled out of the plant cell causing root cells to shrink and collapse 3. High salt concentration itself can be toxic to plants at elevated concentration * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 93  Effects of high salt concentration 4. Low to moderate salinity may actually improve some soil physical condition. Ca and Mg causes soil colloids to flocculate (clump together), thus, increasing aggregation and macroporosity 5. High Na causes soil colloids to disperse or spread out, if sufficient amount of flocculating cations (Ca and Mg) are not present to counteract Na. Dispersed colloids clog pores reducing the soils ability to transport water and air * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 94 Step by step recommendation to reclaim saline soils: 1. Take a salt-alkali soil test to determine specific problem 2. Identify source/cause of problem 3. Eliminate source of contamination, if possible, establish drainage 4. Apply irrigation (flooding) approximately 1 foot high 5. Allow water to percolate and apply another irrigation * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 95 Step by step recommendation to reclaim sodic, saline-sodic soils: 1. Take a salt-alkali soil test to determine specific problem 2. Add chemical amendment (gypsum) (CaSO4. 2H2O), to sodic or saline-sodic soils 3. Incorporate residue to improve water intake * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 96 Gypsum * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 97 Management of sodic soils Exchangeable sodium percentage Gypsum application (ESP) Greater than 5 but less than 10 2-5 tons per hectare Greater than 10 5 tons per hectare * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 98 Step by step recommendation to reclaim sodic, saline-sodic soils: 6. Apply good quality irrigation if available -Apply irrigation to leach the Na+ that is pushed off exchange sites by Ca2+ 7. Allow time for leaching and consider planting tolerant crops * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 99 Moderately Salt tolerant crops 1. Tomatoes 10. onion 2. Coconut 11. pea 3. Rice 12. sorghum 4. Cabbage 13. squash 5. Sweet pepper 14. carrot 6. Lettuce 7. Corn 8. Potato 9. cucumber * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 100 Reaction of gypsum to sodic soils Ca2 SO42 + - Ca+ Ca+ + + - - - - - - - - - Ca+ Na Na Na Ca++ + + + + Na - - - - - + - - - - Na Na+ Na Na + + Na + Na + Na+ Na + Na Na+ + + Na + Na + * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 101 Sulfuric acid* can be used instead of gypsum on calcareous (CaCO3 containing) soil only. Sulfuric acid dissolves calcium carbonate in the soil and makes gypsum! *Sulfuric acid is extremely dangerous and should only be handled by trained personnel. * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 102  END! * PREPARED BY: REUBEN JAMES C. ROLLON, M.SC. 103 104 105 106