micronutrient

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Micronutrients are nutrients needed throughout life in small quantities. They are dietary minerals needed by the human body in very small quantities (generally less than 100micrograms/day) as opposed to macrominerals which are required in larger quantities. The Microminerals or trace elements include at least iron, cobalt, chromium, copper, iodine, manganese, selenium, zinc and molybdenum. Note that the use of the term "mineral" here is distinct from the usage in the geological sciences.

Vitamins are organic chemicals that a given living organism requires in trace quantities for good health, but which the organism cannot synthesize, and therefore must obtain from its diet.

The promise of micro-enriched fertilization

The returns of applying micronutrient-enriched fertilizers could be huge for human health, social and economic development. Research has shown that enriching fertilizers with micronutrients had not only an impact on plant deficiencies but also on humans and animals, through the food chain. A report by the World Bank and the Asian Development Bank stated that eliminating micronutrient deficiencies could:

• improve GDP by more than 5 %;
• enhance the intellectual capacity of populations by more than 10 %;
• enhance worker productivity by 30 to 70 %;
• reduce maternal deaths by up to 50%.
• Food biofortification using plant breeding (genetic biofortification) and/or micronutrient fertilizers (agronomic biofortification) can contribute to this goal.

Addressing zinc deficiencies through zinc fertilization

Experiments show that soil and foliar application of zinc fertilizer can effectively reduce the phytate:zinc ratio in grain. People who eat bread prepared from zinc enriched wheat show a significant increase in serum zinc, suggesting that the zinc fertilizer strategy is a promising approach to address zinc deficiencies in humans.

Where zinc deficiency is a limiting factor, zinc fertilization can increase crop yields. Balanced crop nutrition supplying all essential nutrients, including zinc, is a cost effective management strategy. Even with zinc-efficient varieties, zinc fertilizers are needed when the available zinc in the topsoil becomes depleted.

Micronutrients for plants

There are about eight nutrients essential to plant growth and health that are only needed in very small quantities. These are manganese, boron, copper, iron, chlorine, cobalt, molybdenum, and zinc. Some consider sulfur a micronutrient, but it is listed here as a macronutrient. Though these are present in only small quantities, they are all necessary.

Boron is believed to be involved in carbohydrate transport in plants; it also assists in metabolic regulation. Boron deficiency will often result in bud dieback.

Chlorine is necessary for osmosis and ionic balance; it also plays a role in photosynthesis.

Cobalt is essential to plant health. Cobalt is thought to be an important catalyst in nitrogen fixation. It may need to be added to some soils before seeding legumes.

Copper is a component of some enzymes and of vitamin A. Symptoms of copper deficiency include browning of leaf tips and chlorosis.

Iron is essential for chlorophyll synthesis, which is why an iron deficiency results in chlorosis.

Manganese activates some important enzymes involved in chlorophyll formation. Manganese deficient plants will develop chlorosis between the veins of its leaves. The availability of manganese is partially dependent on soil pH.

Molybdenum is essential to plant health. Molybdenum is used by plants to reduce nitrates into usable forms. Some plants use it for nitrogen fixation, thus it may need to be added to some soils before seeding legumes.

Zinc participates in chlorophyll formation, and also activates many enzymes. Symptoms of zinc deficiency include chlorosis and stunted growth.

Micronutrient deficiencies in crops

Micronutrient deficiencies are widespread. 50% of world cereal soils are deficient in zinc and 30% of cultivated soils globally are deficient in iron. Steady growth of crop yields during recent decades (in particular through the Green Revolution) compounded the problem by progressively depleting soil micronutrient pools.

In general, farmers only apply micronutrients when crops show deficiency symptoms, while micronutrient deficiencies decrease yields before symptoms appear. Some common farming practices (such as liming acid soils) contribute to widespread occurrence of micronutrient deficiencies in crops by decreasing the availability of the micronutrients present in the soil. Also, extensive use of glyphosate is increasingly suspected to impair micronutrient uptake by crops, especially with regard to manganese, iron and zinc.

See also

• List of micronutrients
• Macronutrient (ecology)
• Dietary mineral
• Manganese deficiency (medicine)

External links

• Network for Sustained Elimination of Iodine Deficiency
• The Micronutrient Initiative
• Micronutrients for Sustainable Food, Feed, Fibre and Bioenergy Production
• Micronutrient Malnutrition
• Zinc fertilizer boosts yields and public health in Central Anatolia, Turkey
• Selenium fertilization in Finland
• HarvestPlus program for biofortification