Nutrients limiting plant growth model demonstration
Plants grow in response to the most limiting growth factor. These factors include light, temperature, water, air, and nutrients. The soil provides structure to support the roots, holds and releases water to plants, holds and releases nutrients to plant roots, and recycles nutrients through decomposition of plant and animal residues to form soil organic matter. This is a simple model to demonstrate limiting nutrients. The concept was expressed by Justus von Liebig, a German chemist, using barrel staves to demonstrate that plants grow proportionally to the most limiting nutrient.
Prepare a gallon jug by cutting holes in it with a sharp knife, then obtaining rubber stoppers or corks of different sizes to plug the holes. Use a permanent, bold marker to write the nutrients by the corresponding stopper. Plant essential nutrients are those all plants must have to complete their life cycle.
For the demonstration, remove the stoppers. Hide the holes and words from the students. Have a water source or another gallon jug of water available, and a pan or tub to catch the leaking water. Ask, "How much water will this jug hold?" When students have answered, pour water from the source into the jug. When water begins to run out the bottom hole, students will usually react. Then turn the jug around and note that the amount of water the jug holds represents plant growht and yield. Discuss the limiting nutrient concept. Start plugging holes from the bottom to show that the jug holds more water, representing more plant growth. Remove one stopper (nitrogen or phosphorus). Show that if all nutrients except that one are present, the growth will not go beyond that hole.
| TEKS: Grade 1: 112.3.b9A (Might alter slightly to light, air, nutrients, temperature, soil ...) Grade 2: 112.4.b9A (Might alter slightly to light, air, nutrients, temperature, soil ...) Grade 3: 112.5.b3C, 8 A-D (desertification, deforestation, ant dens, termite mounds, etc.), 11B Grade 4: 112.6.b3C Grade 5: 112.7.b3C Grade 6: 112.22.b3C, 14B Grade 7: 112.23.b12B Grade 8: 112.24.b12C Env Sys: 112.44c5F |
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| Generalized Nutrient Cycle |  |
Plant Essential Nutrients by Source - Essential nutrients are required by all plants to complete their life cycle
| Macronutrients - air and water | Carbon (C), Hydrogen (H), Oxygen (O) |
| Macronutrients - soil | Nitrogen (N), Phosphorus (P), Potassium
(K), Calcium
(Ca), Magnesium (Mg), Sulfur (S) |
| Micronutrients - soil | Iron (Fe), Manganese (Mn), Zinc (Zn), Copper (Cu), Nickel (Ni),Boron (B), Molybdenum (Mo), Chlorine (Cl) |
| Plant beneficial nutrients Beneficial nutrients enhance the growth of some plants. |
Cobalt (Co), Silicon (Si), Vanadium (V), Sodium (Na) |
Mnemonic Devices
| Macronutrients | C HOPKNS CaFe Mg | |
| Micronutrients | B Mn CuZn MoNiCl | Hillbilly (or Adam's Family) Valentine |
Commonly Limiting Nutrients, Most to Least
- Water
- Nitrogen
- Phosphorus
- Iron
- Sulfur
- Some Micronutrients
Question: I teach a soils class and have been teaching the 18 essential plant nutrients and some students show me textbooks that state there are 16 or 17 essential nutrients. Which is correct and where can I go to find supporting evidence? Any great sites with the latest research in soil science?
Response: This is a good question, and one with a lot of history. The main impetus comes from the definition of the word, essential. If essential means that nutrient is required by all plants to complete their life cycle, then the magic number is generally regarded as 16. The distinction is between essential and beneficial. Several more elements become nutrients if they may have a beneficial impact on the growth of some (not all) plants. Where animals are concerned, the definition of essential has not been written so strictly. If any animal needs an element, it is added to the list. This one (of many) of the differences between animal nutritionists and plant physiologists. It was only about 200 years ago that scientists began realizing that plant roots did not eat soil as we eat food. Previous to that time, researchers looked for the (sole) element of growth for plants. The first one recognized was water. Later, it was recognized that air was also needed. The understanding of plant nutrition developed simultaneously with the science of chemistry. The number of essential nutrients also has developed with detection technology: percent, parts per thousand, parts per million, parts per billion, etc. Labs are able to measure quantities that were once undetectable. To complicate matters, plants uptake elements they do not require for growth and development.
There is universal agreement that 16 nutrients are essential for all plants to complete their life cycle. The ICCA competencies include Ni, resulting in 17, because Ni controls the levels of fixed-N products in legumes, and because seeds of cereal plants deficient in Ni are not viable and fail to germinate. If the question is asked, "Are they essential to all plants to complete a life cycle?" The answer from most would be, “No”. Cobalt is essential to electron transport in nitrogen fixation in bacteria associated with legumes. Legumes and some other plants require Co apart from nitrogen fixation. If the question is asked, "Can a legume complete its life cycle without Co?" The answer is, “Yes”. Does Co enhance the growth of legumes? Yes. When 17 or 18 are used, the less stringent definition of essential has been applied.
There are still others, Na, V, Si, that have been found in plants, and that improve the growth of some plants, typically by substituting for (performing the role of) some essential element.
References:
Brady and Weil, 2002, The Nature and Properties of Soils, 13th edition, use the list of 18.
Havlin et al., 1999, Soil Fertility and Fertilizers, 6th ed., use the list of 16 because the others are not required by all plants.
Some online resources that may be useful are given by Brady and Weil. All use the list of 16.
http://www.greenair.com/interpri.htm
http://www.hydrofarm.com/content/articles/factors_plant.html
http://www.soil.ncsu.edu/publications/Soilfacts/AG-439-16/#Micronutrients