Physical Science Applications in Agriculture

1
Physical Science Applications in Agriculture

• Unit
• Physical Science Systems

2
Problem Area

• Agricultural Production Systems

3
Testing Common Substances for pH

• Lesson

4
Ever see limestone being applied on a growers
field?

• What is so important about this powdery
  substance?
• What does it do for the soil?
• Does the composition or type of limestone
  (liquid, dry, palletized) make a difference in
  its effectiveness?

.acadianashell.co.com/OFFLOADING3.JPG
5
Which plant looks healthier?

• Examine the pictures or actual plants that have
  received different levels of fertilizer.
• Which plant looks healthier?
• Which plant would produce better and more
  product?
• How much fertilizer do they apply to get optimum
  growth of our vegetable plants?
• Is there a way to determine this? How?

6
Learning Objectives

1. Define pH and discuss its role in plant
   nutrition.
2. Explain how soils become acidic.
3. Explain how soil pH is measured.
4. Explain why lime is applied to acid soils.
5. Discuss the effectiveness of lime on acidic soils.

7
Terms

• Acid
• Calcium carbonate equivalent
• Cation
• Cation exchange capacity
• Lime requirement
• Percent base saturation
• pH scale
• Soil pH

8
What is pH?

• Soil pH is the measure of acidity or alkalinity
  of the soil.

9
What is the pH scale?

• The pH scale is a fourteen point scale used to
  measure pH.
• A neutral pH is 7.0.
• A solution with a pH between zero and 6.9 is
  considered acid.
• A solution with a pH between 7.1 and 14.0 is
  considered alkaline or base.
• The scale is expressed in logarithmic terms.
• Each unit change in pH corresponds to a tenfold
  change in acidity or alkalinity.
• A pH of 6.0 is 10 times more acidic than a pH or
  7.0.

10
How does pH affect plant nutrition?

• The pH value of soil is important to
  agriculturalists because certain nutrients become
  unavailable to plants if the pH value is too high
  or too low.
• The amount of nutrients that are available is
  dependent upon soil pH.

11
How does pH affect plant nutrition?
12
How do soils become acidic?

• pH is determined by the concentration of hydrogen
  (H) ions and hydroxyl ions (OH-) in the soil
  solution.

13
How do soils become acidic?

• A sample of pure water has an equal number of H
  and OH- and is neutral.
• An acid is a substance that releases hydrogen
  ions.
• When saturated with H, a soil behaves as a weak
  acid.
• The more H held on the exchange complex, the
  greater the soils acidity.

14
Several factors influence soil pH.

• Soil organic matter is continuously being
  decomposed by micro organisms into organic acids,
  carbon dioxide, and water, forming carbonic acid.
  
• Carbonic acid reacts with Ca and Mg carbonates in
  the soil to form more soluble bicarbonates, which
  are leached away, leaving the soil more acid.

15
Several factors influence soil pH.

• As water from rainfall passes through the soil,
  basic nutrients such as calcium and magnesium are
  leached.
• They are replaced by acidic element including
  aluminum, hydrogen, and manganese.

www.goeverett.com/misticbev/assets/images
16
Several factors influence soil pH.

• Soils formed under forest vegetation tend to be
  more acidic than those developed under
  grasslands.

www.itc.nl/personal/.../t1765e0s.htm
17
Several factors influence soil pH.

• Soils often become more acidic when crops are
  harvested because bases are
• removed.
• Legumes generally contain higher levels of bases
  than grasses.
• Legumes also release H ions into their
  rhizosphere when actively fixing atmospheric N.

18
Several factors influence soil pH.

• Nitrogen from fertilizer, organic matter, manure,
  and legume N fixation produces acidity.
• Nitrogen fertilization speeds up the rate at
  which acidity develops.
• At lower N rates, acidification rate is slow, but
  is accelerated as N fertilizer rates increase.

19
ACID AND ALKALINE SOILS
20
How is soil pH measured?

• The two most commonly accepted methods of
  measuring soil pH are indicator dyes and the pH
  meter.

ltpwww.gsfc.nasa.gov...globe/pvg/19-5ph.jpg
21
How is soil pH measured?

• Indicators are frequently used in the field to
  make a rapid pH determination and must be used by
  a trained hand to avoid major error.

• The more accurate and widely used method is the
  pH meter used in soil testing laboratories.

www.bbc.net.uk/garde...asics/soil_test7.jpg
22
Why is lime applied to acidic soils?

• Since various plants require different pH levels
  for optimum growth, growers must attempt to
  adjust soil pH to suit the crop or plant being
  grown.
• This involves the use of limestone to raise pH or
  the use of alum to lower pH.
• Lime requirement is the amount of agricultural
  limestone needed to establish the desired pH
  range.

23
Why is lime applied to acidic soils?

• Soil pH is an excellent single indicator of soil
  acidity, it does not determine lime requirement.
• Lime requirement of a soil is not only related to
  the pH but also to its buffer capacity or cation
  exchange capacity.
• Cation exchange capacity is the total number of
  exchangeable cations, an ion with a positive
  charge, a soil can adsorb.
• The relative amount of the cation exchange
  capacity filled with basic cations is called
  percent base saturation.
• Soil pH is a measure of the percent base
  saturation.

24
Why is lime applied to acidic soils?

• Lime replaces hydrogen and aluminum on the cation
  exchange sites with calcium and changes hydrogen
  ions to water.

www.imdexminerals.com.au/ag.asp
25
Factors to figure how much lime is required

• the present pH
• the desired pH
• the cation exchange capacity of the soil
• the liming material to be used

www.hort.wisc.edu/.../soiltest/soiltest.htm
26
The effectiveness of lime on soil.

• The effectiveness of lime depends on
• Purity
• Fineness
• Rate it dissolves
• Measured as the calcium carbonate equivalent

27
What determines the effectiveness of lime on acid
soils?

• The neutralizing power of lime depends upon its
  purity, measured as the calcium carbonate
  equivalent.
• Neutralizing values of all liming materials are
  determined by comparing them to the neutralizing
  value of pure claim carbonate.
• Setting the neutralizing value of calcium
  carbonate at 100, a value for other materials can
  be assigned.

28
What determines the effectiveness of lime on acid
soils?

• When a given quantity of lime is mixed with the
  soil, its reaction rate and degree of reactivity
  are affected by particle size.
• Coarse live particles react more slowly and less
  fully.
• Fine lime particles react more rapidly and much
  more completely.
• Cost of lime increases with the fineness of
  grind.
• The goal is a material that requires a minimum of
  grinding, yet contains enough fine material to
  cause a rapid pH change.

29
Other important factors determining the
effectiveness of lime

• Placement for maximum contact with the soil in
  the tilled layer is essential.
• Even when properly mixed with the soil, lime will
  have little effect on pH if the soil is dry.
• Moisture is essential for lime-soil reaction to
  occur.
• The full benefit of lime is not seen until the
  second or third year after application.
• Lime does not react with acidic soil very far
  from the lime particle.

30
Review/Summary

• What is pH and how does it affect plant
  nutrition?
• How do soils become acidic?
• How is soil pH measured?
• Why is lime applied to acidic soils?
• What determines the effectiveness of lime on acid
  soils?