Soil ph and Salinity. Chapter 11

Transcription

1 Chapter 11 Soil ph and Salinity

2 Objectives After completing this chapter, you should be able to: Describe soil ph and its development Describe how ph affects plant growth Tell how to lime or acidify soil Perform lime calculations Describe saline and sodic soils Describe methods to treat and manage saline and sodic soils

3 Soil reaction Soil ph Acidity or alkalinity of a soil Affects plant growth greatly Measured using the ph scale ph scale ph measures acidity/alkalinity Acidic: 0 to below 7.0 Neutral: 7.0 Alkaline: 7.0 to 14.0

4 Soil ph (cont d.) The math and chemistry of ph Negative logarithmic value of hydrogen ion concentration in moles per liter p stands for negative log H stands for hydrogen ion concentration

5 Development of Soil ph Most acidic soils have a ph of 3.5 Most basic soils are about 10.5 Soil ph Results from the interaction of soil minerals, ions in solution, and cation exchange High ph is caused by the reaction of water and basic compounds of calcium, magnesium, and sodium forming hydroxide ions Low ph is caused by the percolation of mildly acidic water

6 Include: Causes of Acidity Young soil that has not been exposed to lengthy weathering/leaching Acidic parent materials Rainfall Plant respiration Nitrification Nitrogen cycling and farming fertilizers Decay

7 Include: Effects of ph on Plants Nutrient availability Affects solubility Element toxicity Inhibits root growth Soil organisms Inhibits growth of organisms

8 Liming Soil Used to alter acidic soil Improves crop response to fertilizers by improving nutrient uptake, especially phosphorus, reducing aluminum toxicity, and promoting the activities of desirable organisms

9 Materials Liming Soil (cont d.) Calcitic limestone Dolomitic limestone Burned lime Hydrated lime Marl Ground seashells Industrial by-products Wood ash

10 How lime works Liming Soil (cont d.) Lime neutralizes soil in two ways Anion base (carbonate, hydroxide, oxide) neutralizes acidity by accepting hydrogen ions from the soil solution and making them part of water molecules Calcium (or magnesium) replaces hydrogen and aluminum ions on exchange sites by mass action, freeing them into the soil solution, allowing them to be neutralized

11 Buffering Capacity Factors that determine lime amount Present ph Desired ph Buffering capacity Liming material Effect of buffering capacity on liming The greater the buffering capacity, the more lime that will be needed

12 Buffer tests Lime Calculations Determine lime needs based on average calcitic limestone/calcium carbonate Total Neutralizing Power (TNP) or Calcium Carbonate Equivalent (CCE) Compares agricultural lime with pure calcium carbonate

13 Fineness Lime Fineness Affects how rapidly lime neutralizes acidity Finer are more reactive Effective Neutralizing Power (ENP) Calculates application rates

14 Effective Neutralizing Power Final measure of how effective a lime product is at neutralizing acidity Calculated as a percent of the effectiveness of pure calcium carbonate that is ground fine to be 100 percent effective % ENP = % CCE FI % Dry Matter Other lime calculations Application rate Prices

15 Best results Lime Application Obtained from liming when there is close contact between the grains of lime and the soil Lime should be spread evenly over the field and then mixed well into the soil Can be spread dry, as pellets, or in fluid form

16 Acidifying Soil Sometimes soil can be too basic for good plant growth May occur with acid-loving plants preferring a ph range from 4.0 to 5.5 Parts of the country where soil is naturally too alkaline Sulfur Used for long lasting ph reduction A number of other chemicals also acidify the soil

17 Humid regions Soil Salinity Acidity is a common problem Percolation leaches calcium, magnesium, and sodium Arid regions Accumulation of soluble salts

18 Include: Effects of Soil Salts Osmotic effects Root stress/rot Ion-specific effects Nutrient imbalances Inhibited microorganisms Extremely high ph

19 Saline Soils High levels of soluble salts except sodium Measured by passing an electrical current through a solution extracted from a soil sample Electrical conductivity The greater the salt content, the greater the electrical current Saline soil Defined as a soil with an EC of four or more millimhos per centimeter

20 Sodic Soils Lower in the kinds of salts found in saline soils but high in sodium Sodium is often measured by the sodium adsorption ratio Compares concentration of sodium ions with the concentration of calcium and magnesium ions

21 Saline-Sodic Soils Contain high levels of both soluble salts and sodium EC is greater than 4.0 millimhos per centimeter SAR is greater than 13 ph is less than 8.5

22 Reclaiming Salted Soils Steps in reclamation of salted soils Decide whether the project is practical and will pay for itself Ensure good drainage to allow salted water to leave the soil profile After proper drainage has been installed, the next steps depend on the type of problem

23 Considerations Managing Salted Soils Use high-quality irrigation water Keep soil moist Over-irrigate enough to leach salts out of root zones Avoid overfertilization Maintain a good soil-testing program Plant on ridge shoulders in furrow-irrigated fields Use drip irrigation

24 Considerations Salted Water Disposal Improve irrigation Collection of drainage in evaporation ponds

25 Managing Salts in Potted Plants Considerations Frequent monitoring of EC with conductivity meters Irrigation Fertilizers

26 Summary This chapter reviewed several topics Soil ph depends on the balance of hydrogen and hydroxyl ions in the soil solution Too acidic, alkaline, or saline soil produces plant growth problems Liming reduces soil acidity Sulfur reduces soil alkalinity Flooding and leaching may be used to reduce salt in soil