1 / 63

SOIL Ph and Salinity

ami
Download Presentation

SOIL Ph and Salinity

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

    1. SOIL Ph and Salinity Chapter 11

    2. Soil pH Soil reaction describes the acidity or alkalinity of the soil pH of 0 to 7 is acid pH of 7 to 14 is base or alkaline 7 is neutral pH is the negative log of the H ion concentration

    3. Testing for pH

    4. Soil Reaction H2O ??H+ + OH- Water hydrogen ion hydroxyl ion In pure water cations = anions Pure water is neutral Dissolved materials will ionize and change balance

    5. Soil Reaction CO2+H20?H2CO)3?HCO3- + H+ Carbon dioxide from the air combines with water to form carbonic acid The excess H atoms cause the solution to be acidic Each scale point multiplies acidity or alkalinity by 10 pH of 6 is 10 x more acid than pH of 7

    6. Common Solutions pH common solution 1 hydrochloric acid 2 lemons, vinegar 3 4 tomatoes 5 boric acid 6 milk

    7. Common Solutions pH common solution 7 neutral 8 sea water, bicarb of soda 10 milk of magnesia 11 ammonia 13 lye

    8. Acid pH

    9. Acid pH

    10. Neutral pH

    11. Basic pH

    12. Basic pH

    13. Soil Reactions (c & d) CaCO3+2H2O?Ca+2+H2CO3+2OH- Calcium carbonate + 2 water? calcium+ carbonic acid + 2 hydroxyls Na2CO3+H2O?2Na++H2CO3+2OH- Sodium carbonate + water = sodium + carbonic acid + 2 hydroxyls This is called Hydrolysis

    14. Soil Reaction (e)

    15. Hydrogen Exchange Reaction (f)

    16. Reactions That Determine pH pH range Reaction Saturation 8.5-10.0 Na2CO3 100%base 15%Na 8.0-8.5 CaCo3 100%base calc. 7.0-8.0 Exch.Ca <100%base 6.0-7.0 H Exch. <100%base 4.0-6.0 Al hydr. Low base, high Al

    17. Al Ion Reactions (g) (h) Al+3 + 2H2O?Al(OH)2+1 +2H+ Aluminum hydrolysis lowers pH to about 4. This is the most acidic soil

    18. Percolating Water in Young Soils Leaches Away Bases (I) micelle—Ca+2+ 2H+?micelle H++ Ca+2

    19. Percolating Acid Water Causes H Ions to Replace Ca & Mg These bases then leach away This happens in humid climates

    20. Leaching In humid climates, rain exceeds evapotranspiration Net water movement is downward Soil become acid In semi-arid climates, evapotranspiration exceeds rainfall Net water movement is upward Soil becomes alkaline

    21. Respiration of Roots Can Acidify Soil CO2 from roots combines with water to form carbonic acid (j) CO2+H2O?H2CO3?HCO3-+H+ Nitrifying bacteria form ammonia which combines with water + H ions (K) NH4++2O2?NO3-+H2O+2H+

    22. pH for Field Crops Cowpea 5.0-7.0 Cotton 5.5-6.4 Peanut 5.3-6.8 Oats, rye 5.6-7.5 Soybean 5.5-7.0 Corn. Sorghum, wheat 6.0-7.5 Barley 6.5-7.5

    23. pH for Vegetables Potato 5.0-5.5 Cabbage 5.5-7.0 Carrots 6.0-6.9 Cauliflower 6.0-6.9 Tomato, lettuce 6.0-7.0 Muskmelon 5.8-7.0 Asparagus 6.0-6.9

    24. pH for Forage Crops Alsike clover 5.0-7.0 Vetch 5.5-6.6 Red clover,Sudan 5.5-7.0 Timothy 5.8-7.0 White clover 6.0-7.5 Sweet clover 6.5-7.5 Alfalfa 7.0-8.0

    25. pH for Fruits and Ornamentals Blueberry 4.0-5.0 Azalea 4.5-5.0 Strawberry 5.5-6.5 Pin oak 5.0-6.5 Jap yew 6.0-7.0 Sugar maple 6.0-7.5 Black walnut 6.0-8.0

    26. Soil Conditions Related to pH Play an Important Part The effect of pH on nutrient availability The buildup of toxic levels of aluminum Effects on soil microbes

    27. Effects of pH on Nutrient Availability The best general range for most plants is 6.0-7.0 See handout, discuss

    28. Ph and Element Toxicity Below 5.5 high (toxic) levels of aluminum occur Fe and Mn become more available Note acid loving plants show deficiencies at higher pH range Soil organisms grow best at neutral pH

    29. Liming Soil Match the crop to the soil pH or: Change the pH Liming will raise pH Sulfur will lower pH Nitrogen fertilizers lower pH

    30. Applying Line to Soils

    31. Liming Materials: Agricultural Lime Calcitic limestone=CaCO3 Dolomitic limestone= CaCo3 &MgCo3 Burned lime=CaCo3?CaO+Co2 gas Hydrated lime=CaO+H2O?Ca(OH)2 Marl=soft chalky fresh water deposits Ground seashells Slag from iron smelting….wood ashes

    32. How Liming Works Ca replaces H and Al on exchange sites See figure 10-10 4Ca(OH)2?4Ca+2 +8(OH-) The free Al combine with water to make aluminum hydroxide The free H combines with hydroxyls to form water (H2O

    33. How Liming Works 4CaCO3?4Ca+2 +4(CO3-2) Same as before but with a carbonate CO3- combine with H to make unstable carbonic acid which breaks down to form CO2 gas and water

    34. You Need to Know The existing pH Desired pH Cation exchange capacity of the soil What liming material will be used

    35. pH buffering in the soil

    36. #Lime/1000 sq feet needed Text. class 4.5 to 5.5 5.5 to 6.0 Sand, loamy sand 25 30 Loam 45 55 Silt loam 80 105 Clay loam 100 120 Muck 200 225

    37. Buffer Indexes: Tons of Lime/Acre Buffer pH mineral organic 7.0 0 0 6.8 1.0 0 6.6 2.0 0 6.4 3.0 1.0 6.2 4.0 2.5 6.0 5.5 4.0 5.8 6.5 5.0 5.6 8.0 6.0

    38. How Much to Apply Soil tests give amount of CaCo3 needed in # or tons per acre Add all atomic weights =100 Divide the weight of the substitute by 100 and this will give the X amount of the substitute needed. This is called the CCE Calcium carbonate equivalent It could be more or less than the original

    39. Forms of Lime Form 100% Neutralizing Value Calcium carbonate 100 Magnesium carbonate 119 Hydrated lime 172 Burned lime 178

    40. Forms of lLme Calcitic limestone 85 85 Dolomitic limestone 85 88 Hydrated lime 85 115 Burned lime 151 Marl 50-70 Basic slag 60-90 Wood ashes 45-80 Ground seashells 85 85

    41. Lime Particle Size 100- 80- 60- 40- 20- 0-

    42. Acidifying the Soil Sulfur is the preferred material Thiobacillus bacteria convert sulfur to sulfuric acid 2S + 3O2 + 2H2O?2H2SO4 + energy The sulfuric acid releases H ions and the soil becomes more acid.

    43. Amount to Use/ 8” soil To lower pH pts/100sq ft lbs/acre This amount sand loam sand loam 0.5 2/3 2 360 1100 1.0 1 1/3 4 725 2200 1.5 2 5 ½ 1100 3000 2.0 2 ½ 8 1350 4400 2.5 3 10 1650 5400

    44. Acidifying the Soil Other materials are available Iron sulfate Fe2(SO4)3 Aluminum sulfate Al2(SO4)3 Calcareous soils would require more because of large reserve alkalinity

    45. Soil Salinity Acid soils occur in humid areas because Ca,Mg, and Na leach out Saline soils are common in arid regions HCL + NaOH?H20 + NaCl Acid base water salt A soluble salt is one that is more soluble than gypsum CaSO4

    46. Salts of Greatest Concern Calcium sulfate CaSO4 Sulfates SO4-2 Bicarbonates HCO3- Chlorides Cl- of Ca Mg Na Usually in the southwest Greenhouses

    47. Salinity is Measured with Electric Current Soil cond. Exch Na abs soil Class mmhos Na ratio pH Saline >4.0 <15 <13 <8.5n Sodic <4.0 >15 >13 >8.5p Saline/ >4 >15 >13 <8.5n sodic

    48. Sodic Soils Low in saline salts High in sodium Sodium 15> pH 8.5 – 10.0 SAR= sodium adsorption ratio

    49. SAR SAR= [Na+]

    50. SAR Water held at wilting point 50%

    51. Crop Response to Soil Salinity Class salinity crop response Nonsaline 0-2 not important Slt saline 2-4 sensitive crops< Mod saline 4-8 many crops< Strng saline 8-16 only tolerant> V strng 16> most tolerant>

    52. Crop Response to Salinity: Field Crops Tolerant Medium Sensitive Barley corn beans Sugar beet soybean flax Cotton sorghum broadbean

    53. Crop Response to Salinity: Forage Crops Tolerant Medium Sensitive Bermuda grass alfalfa clovers Wheatgrass orchard grass Tall fescue perennial rye

    54. Crop Response to Salinity: Vegetable Crops Tolerant Medium Sensitive Beets spinach lettuce Asparagus tomato bell pepper Broccoli onion Cabbage carrot Potato beans Sweet corn celery

    55. Crop Response to Salinity: Fruit Crops Tolerant Medium Sensitive Date palm Grape all others Fig Olive

    56. Sodic Soil Na reacts with water to form lye Na destroys soil structure (can be used to seal ponds) Most destructive on fine soils

    57. Saline Sodic Soils High levels of salts and sodium Conductivity>4.0 millimhos/cm SAR>13 pH<8.5 May become sodic with leaching

    58. Recovering Salted Soil Is it worth the cost? If good drainage, may leach Subsoil hardpans Lower high water tables Use organic mulches

    59. Recovering Sodic Soils Treat with gypsum Ca replaces Na on exchange sites Sulfur can be used Changes to sulfuric acid H ions replace sodium

    60. Ca Exchanges for Na Sodium sulfate leaches out

    61. Using Sulfur If soil contains some lime CaCO3 Finely ground sulfur converts to sulfuric acid H ions replace Na at exchange sites CaCO3+H2SO4?CaSO4+H2O+CO2 gas

    62. Managing Salted Soils Prepare field for irrigation Use high quality water Keep soil moist Over-irrigate to leach Avoid over fertilization Use O.M., test often Plant on ridges, trickle irrigate

    63. Furrow Irrigated Fields Planting should by done on shoulders of furrows, top has highest salt content

    64. Trickle Irrigation Trickle irrigation reduces salt stress Dissolved salts move away by capillary action

More Related