understanding soil chemistry
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Understanding Soil Chemistry. Importance of Soil Fertility. Soil Fertility Ability of a soil to provide nutrients for plant growth Involves storage and availability of nutrients Vital to a productive soil Fertile soil is not necessarily a productive soil Why?

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importance of soil fertility
Importance of Soil Fertility
  • Soil Fertility
    • Ability of a soil to provide nutrients for plant growth
    • Involves storage and availability of nutrients
    • Vital to a productive soil
      • Fertile soil is not necessarily a productive soil
        • Why?
      • Poor Drainage, Insects, Drought, and other factors can limit production
importance of soil fertility1
Importance of Soil Fertility
  • Existing plant-soil relationships affect soil productivity
    • External factors control plant growth
      • Air
      • Temperature
      • Light
      • Mechanical support
      • Nutrients
      • Water
  • Plants rely on soil to provide all these except light
importance of soil fertility2
Importance of Soil Fertility
  • Water and air fill pore spaces in soil
    • Factors that affect water relationships also affect soil air
  • Nutrient availability is influenced by soil and water balance and temperature
  • Root growth is influenced by soil temperature as well as soil, water, and air
role of organic matter
Role of organic Matter
  • What is organic matter?
    • Plant, animal, and microbial residues
      • Varying stages of decay
  • Adequate levels of O.M. benefit soil by:
    • Improving physical condition and tilth
    • Increases water infiltration
    • Decreases erosion loss
    • Supplies plant nutrients
role of organic matter1
Role of organic Matter
  • Organic matter contains about 5% N
    • N is not immediately available
    • Decomposition must occur first
  • Fertilizer (inorganic) N is needed for non-legume plants
  • Organic matter also provides soil with a variety of other mineral elements that plants need to be healthy
    • Some include: phosphorus, magnesium, calcium, sulfur, and others
role of soil depth
Role of Soil Depth
  • Soil Depth
    • Depth of soil material favorable for plant root penetration
  • Plants need soil to be:
    • Deep
    • Well-drained
    • Correct texture
    • Correct structure
  • Deeper soils provide for more nutrient storage
role of soil depth1
Role of Soil Depth
  • Roots can extend 3-6 feet or more when soil depth permits
    • Rooting depth is affected by
      • Physical barriers
      • Chemical barriers
      • High water tables
  • Hardpans, Shale beds, Gravely Layers and accumulations of salts are very hard to correct
role of surface slope
Role of surface Slope
  • Surface slope is part of what?
    • Topography
  • Determines the amount of runoff and erosion
  • Also determines:
    • Irrigation method
    • Drainage
    • Conservation practices
  • The steeper the land the more management is needed
    • More labor and equipment costs
role of surface slope1
Role of surface Slope
  • At certain slopes, soil is no longer suitable for row crops.
    • What are some row crops?
  • Potential productivity is largely determined by ease of erosion along with percent of slope
role of soil organisms
Role of Soil Organisms
  • Many different organisms live in the soil
    • Usually in the first foot of top soil
    • Depend on organic matter for food
  • Factors that affect the amount soil organisms:
    • Moisture
    • Temperature
    • Aeration
    • Nutrient supply
    • Soil pH
    • Crop that is being grown
role of soil organisms1
Role of Soil Organisms
  • Some of the microscopic organisms cause many favorable soil reactions
    • decay of plant and animal residues
    • speed nutrient cycling.
  • Other reactions can be injurious
    • development of organisms that cause plant and animal diseases
role of nutrient balance
Role of Nutrient Balance
  • Nutrient balance is a vital concept in soil fertility and crop production
  • Nitrogen is the first limiting nutrient in non-legumes
  • Without adequate amounts of the other nutrients, N cannot do its best
  • As Nitrogen fertilization raises yields, the crop demands more of the other nutrients
soil ph
Soil pH
  • The measure of acidity or alkalinity of the soil
  • pH is determined by the concentration of hydrogen ions(H+) and hydroxyl ions(OH-) in the soil solution
  • Pure water has an equal number of H+ and OH-
soil ph1
Soil ph
  • Another term for alkaline is basic
  • Acid = high in H+
  • Basic = high in OH-
  • A soil with a pH of 6.0 has 10 times as much active H+ than neutral
soil ph2
Soil ph
  • Plants will not thrive in soil that is too acid or too alkaline
    • The soil pH directly affects the availability of mineral nutrients
  • Example
    • Low pH: phosphates may be bound chemically in the soil so plants are unable to access them
      • Also means that nitrate production in the soil is reduced
soil ph3
Soil PH
  • Several factors influence Soil pH
    • Organic matter
    • Parent material
    • Rainfall
      • leaching
    • Forest vs. grassland
    • Harvesting crops
    • Legumes
    • Soil depth
    • Fertilizer application
    • Flooding
soil ph4
Soil ph
  • How to measure soil pH
    • Indicator dyes
    • pH meter
  • Which do you think is more accurate?
  • The meter
  • If our soil’s pH was too acidic what would we add to amend it?
    • Lime
lime requirement
Lime requirement
  • Soil pH is not the determining factor on how much lime to add
    • What else do we need to consider?
      • Texture of soil
      • Amount of organic matter
  • The amount of clay and organic matter in a soil will determine the ability of a soil to resist pH change
    • More clay/organic matter = more pH buffering
  • The process is very complex
    • Example: Al and water
lime requirement1
Lime requirement
  • Lime requirement
    • Amount of Ag limestone needed to establish the desired pH range for the cropping system being used
  • Lime reduces soil acidity
    • Look at Al and water example
    • Uses Ca ion
  • Soil will become more and more acidic if a liming program is not followed
  • We do not apply lime to soils here in Northern Utah very often… Why?
lime requirement2
Lime Requirement
  • In the case of high pH
    • Lowering pH is not usually economical
  • These are generally high in salts
    • Find plants that tolerate high salt levels
cation exchange capacity
Cation Exchange Capacity
  • As soils form
    • Some particles are broken down into extremely small particles
  • Chemical weathering breaks them down until they cannot be seen with the naked eye
    • The smallest are called colloids
  • Colloids are responsible for chemical reactivity in soil
  • Each colloid has a negative(-) charge
cation exchange capacity1
Cation Exchange Capacity
  • The neg. charge will attract positively(+) charged particles
    • What does that mean if they run into another negative?
  • Cations: Positive Charge
  • Anions: Negative Charge
  • Colloids act like a magnet and holds cations
    • Other cations can take their place
    • They are exchangeable
cation exchange capacity2
Cation Exchange Capacity
  • Can a soil hold more cations than it has colloids?
    • no
  • We need to know our soil’s CEC
  • Higher CEC = more cations can be held
  • Depends on clay and organic matter
    • Lots of clay = higher CEC
    • More organic matter = higher CEC
cation exchange capacity3
Cation Exchange Capacity
  • Leaching is reduced by higher CEC
  • Knowing our CEC will help determine how much fertilizer to apply and how often
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