Chapter 7

Nutrients

OBJECTIVES

After completing this chapter, you should be able to:

• Name the essential plant nutrients and describe their role in plant growth
• Explain how plant nutrients behave in soil
• List plant nutrients and fertilizer materials that are compatible with the environment
• Describe soil testing for determining plant nutrient needs and fertilizer sources
• Discuss how plant nutrients behave in the soil Describe what soil pH is and how it is managed
• Name the sixteen elements essential for plant growth
• Categorize the sixteen essential elements into those supplied by the air and water, primary nutrients, secondary nutrients, and micronutrients
• Draw the nitrogen cycle
• Describe the effect organic matter has on soil fertility
• Discuss how soil pH influences the availability of nutrients
• Describe the deficiency signs of five nutrients
• Explain how many pounds of nitrogen, phosphate, and potash are in a hag of fertilizer
• Use conversion factors when working with fertilizers
• List five types and sources of fertilizers

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KEY TERMS

Name the essential plant nutrients and describe their role in plant growth.

Non-mineral Nutrients - Carbon, Hydrogen, and Oxygen - also Nitrogen

1. Carbon comes from CO₂ out of the atmosphere and is the major structural element of organic compounds.
2. Hydrogen comes from water and bonds to the carbon molecular skeleton.
3. Oxygen comes from CO₂ and water and bonds to the carbon molecular skeleton.

Carbohydrates (sugars, starches, cellulose, etc) for the basic building blocks of cells and are made up of these three elements. These molecules are converted to more complex molecules (amino acids, proteins, lipids, enzymes, etc)  by the addition of other nutrient elements.

Macronutrients

    Primary nutrients (fertilizer elements) - Nitrogen, Phosphorus, and Potassium

1. Nitrogen is a primary constituent of amino acids and proteins. Since enzymes and membranes are protein-based structures, a nitrogen deficiency will curtail plant growth.
2. Phosphorus is a constituent of ATP and ATP, the energy-containing molecules that are present in respiration and photosynthesis.
3. Potassium is a salt. It is very mobile in the plant and seems to be involved in transport operations.

    Secondary nutrients - Calcium, Magnesium, Sulfur

1. Calcium is a constituent of cell walls. Since cell division requires the building of new cell wall material, a deficiency of calcium will show  up in the meristem.
2. Magnesium is a component of chlorophyll. It is also present in vitamins.
3. Sulfur is a component in certain amino acids and vitamins.

Micronutrients - Boron, Chlorine, Copper, Iron, Manganese, Molybdenum, and Zinc

1. Boron - flowering, fruiting, and cell division
2. Chlorine -
3. Copper - Enzymes that  are involved in the synthesis of chlorophyll
4. Iron - A catalyst in chlorophyll formation
5. Manganese - synthesis of chlorophyll
6. Molybdenum - protein synthesis
7. Zinc - needed for auxin and starch formation

Explain how plant nutrients behave in soil.

• Nutrients are taken up by the plant as ions, that is, charged atoms or molecules.
• In the soil, the nutrients interact with each other, with the mineral and organic soil particles, and with microorganisms.
• Some are prone to form relatively insoluble compounds while others remain in solution.
• Others are held by soil particles.
• Some are modified by microorganisms.
• Most of the above characteristics are modified or regulated by soil pH and eH.

List plant nutrients and fertilizer materials that are compatible with the environment

All plant nutrients are compatible with the environment. Some fertilizers, when applied at the wrong time, or in quantities that are too great, or forms that are too mobile, have the potential to contaminate surface waters or groundwater. 

Organic nutrients, especially those that result from composting, are the most environmentally friendly in most circumstances, assuming that there are no large quantities of heavy metals or other toxic substances that might come from industrial waste.

Describe soil testing for determining plant nutrient needs and fertilizer sources

Soil testing reveals the soil's reaction (pH), organic matter content, and the nutrient status. With this knowledge, the quantities of nutrients that will be available to a crop can be estimated. 

By knowing the requirements of the crop to be grown, fertilizer management decisions can be made. The goal is to provide the crop with as much nutrient as it will require, without providing too much.

Discuss how plant nutrients behave in the soil

Nitrogen forms are mobile, the nitrate anion being more mobile than the ammonium ion, which can undergo cation exchange. There are many microbial interactions with nitrogen containing substances.

Phosphorus is relatively immobile. It forms relatively insoluble compounds with calcium and magnesium and high pH's and iron and aluminum at low pH's. Only a very small percentage of the total phosphorus in the soil is soluble and available for plant uptake. (as HPO₃⁼ and H₂PO₃^-, the hypophosphate anions)

Potassium is a component of many soil minerals. As a result, many soils release potassium to the plant as they weather. However, potassium is utilized in fairly large amounts by plants, so its addition as fertilizer is often required. It is taken up by the plant as the ion K⁺. This ion can undergo cation exchange, and some of it can be leached by percolating soil water. There are some clay minerals that fix potassium ion almost irreversibly.

The degree of mobility and availability of elements in the soil is a complex interaction of soil moisture content, pH, oxidation potential, electrical conductivity, organic matter content, and the chemical activities of all other soil constituents, and the biological activities of microorganisms.

Name the sixteen elements essential for plant growth

C, O, H <=====> N, P, K <===> Ca, Mg, S <=====> B, Cl, Cu, Fe, Mn, Mo, Zn 

The micronutrients: (Boring Classes Caused Fred Many More Zits)

Categorize the sixteen essential elements into those supplied by the air and water, primary nutrients, secondary nutrients, and micronutrients

• Air - C, O, (N)
• Water - H, O
• Primary nutrients - N, P, K
• Secondary nutrients - Ca, Mg, S
• Micronutrients - Bo, Cl, Cu, Fe, Mn, Mo, Zn

Draw the nitrogen cycle

• Here is a link to the nitrogen cycle diagram.

• Note the following forms of nitrogen: 
  N₂, NO₃^-, NO₂^-, NH₃^-, NH₄⁺, Organic N, and NO_x
• Note the following transforming processes: 
  Nitrification, Denitrification, Volatilization, Leaching, Fixation, Exchange, Uptake.

Describe the effect organic matter has on soil fertility

Organic matter contains most of the minerals that plants require. As the material decompose (mineralized), these mineral nutrients are released for uptake by plants. This decomposition is done by soil microorganisms, which also utilize some of the nutrients to produce cells. (Organic matter also increases cation exchange capacity, water-holding capacity, increases infiltration, and imparts better tilth to the soil.)

For the most part, incorporation of organic residues increase soil fertility. If unprocessed organic materials with a high C:N ratio are incorporated into the soil, there will be a temporary nitrogen deficiency induced because the microorganisms are tying up nitrogen (from the soil) in order to build more cells to process the material.

Discuss how soil pH influences the availability of nutrients

The pH of the soil determines to a great extent the chemical forms in which many plant nutrients exist. Some of these forms are more or less soluble, depending on the nutrient. In cases of extreme pH ranges in either direction, some of the micronutrients are unavailable, while others are available in toxic quantities.

Describe the deficiency signs of five nutrients

See this web-site for some excellent photos of nutrient deficiencies. 
Symptoms include patterns of chlorosis, various styles of color changes, leaf curling, necrosis, and stunting
Also note the information below from University of Illinois at Urbana-Champaign

Explain how many pounds of nitrogen, phosphate, and potash are in a hag of fertilizer

Use conversion factors when working with fertilizers

List five types and sources of fertilizers

1. Straight material - contains only one nutrient source
2. Mixed or complete fertilizer - contains more than one nutrient source
3. Solid fertilizer - in the chemical compound form
4. Liquid fertilizer - in the soluble form
5. Animal manures and other organics

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 The following information was lifted from http://www.extension.uiuc.edu/~vista/html_pubs/hydro/symptoms.html

Symptoms of Nutrient Deficiencies

Plants will usually display definite deficiencies if required nutrients are not present in adequate concentrations. The following symptoms may occur if the level of one mineral nutrient is not high enough to be within the range needed for best plant growth. A plant may exhibit a particular symptom for reasons other than a nutrient deficiency. However, if one of the deficiency symptoms occurs, a lack of the proper nutrient may be suspected, and the amount of that nutrient should be increased.

Deficient nutrient	Symptoms
Nitrogen	Leaves are small and light green; lower leaves lighter than upper ones; not much leaf drop; weak stalks.
Phosphorus	Dark-green foliage; lower leaves sometimes yellow between veins; purplish color on leaves or petioles.
Potassium	Lower leaves may be mottled; dead areas near tips and margins of leaves; yellowing at leaf margins continuing toward center.
Calcium	Tip of the shoot dies; tips of young leaves die; tips of leaves are hooked-shaped.
Magnesium	Lower leaves are yellow between veins (veins remain green); leaf margins may curl up or down or leaves may pucker; leaves die in later stages.
Sulfur	Tip of the shoot stays alive; light green upper leaves; leaf veins lighter than surrounding areas.
Iron	Tip of the shoot stays alive; new upper leaves turn yellow between veins (large veins remian green); edges and tips of leaves may die.
Manganese	Tip of the shoot stays alive; new upper leaves have dead spots over surface; leaf may apear netted because of small veins remaining green.
Boron	Tip of the shoot dies; stems and petioles are brittle.

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