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Understanding Soil Chemistry

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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Understanding Soil Chemistry

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  1. Understanding Soil Chemistry

  2. 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

  3. 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

  4. 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

  5. Understanding Soil Chemistry Soil Productivity

  6. 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

  7. 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

  8. 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

  9. 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

  10. 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

  11. 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

  12. 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

  13. 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

  14. 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

  15. Understanding Soil Chemistry Soil pH

  16. 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-

  17. 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

  18. 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

  19. Soil PH • Several factors influence Soil pH • Organic matter • Parent material • Rainfall • leaching • Forest vs. grassland • Harvesting crops • Legumes • Soil depth • Fertilizer application • Flooding

  20. 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

  21. 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

  22. 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?

  23. 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

  24. 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

  25. 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

  26. 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

  27. 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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