| MadSci Network: Botany |
All plants require at least 17 essential elements. Roughly 90% of plant dry weight is composed of carbon, oxygen and hydrogen. Plants obtain those three elements from water and carbon dioxide gas. The other 14 essential elements are obtained mainly from the soil and are often termed mineral nutrients. They are divided into macronutrients and micronutrients. Macronutrients are needed in relatively large amounts, 0.1% or more of the dry weight. Micronutrients are needed in much smaller amounts, 100 parts per million or less. The six mineral macronutrients are nitrogen, phosphorus, potassium, calcium, magnesium and sulfur. Carbon, hydrogen and oxygen are also considered macronutrients. The eight micronutrients are iron, boron, manganese, zinc, copper, molybdenum, chlorine and nickel. If the beans are using bacterial nitrogen fixation, then the nitrogen-fixing bacteria require cobalt. Most plants naturally absorb large amounts of silicon. Silicon plays several beneficial roles in plants but is not considered essential. Chlorine and nickel deficiencies have never been found under natural conditions because those two elements are so widespread in soils and plants require relatively little. Therefore, chlorine and nickel are not usually added to fertilizers. The first website in the references section provides a lot more detail on essential elements for plants. Another good search term in plant nutrition. References Essential Elements for Plant Growth Epstein, E. 1994. The anomaly of silicon in plant biology. Proc. Natl. Acad. Sci. USA. 91: 11–17. Plant nutrition
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