|Fageria, N - EMBRAPA BRAZIL|
|Clark, R - USDA-ARS (RETIRED)|
Submitted to: Advances in Agronomy
Publication Type: Review Article
Publication Acceptance Date: July 12, 2001
Publication Date: N/A
Technical Abstract: The essential micronutrients for field crops are B, Cu, Fe, Mn, Mo, and Zn. Other mineral nutrients at low concentrations considered essential to growth of some plants are Ni and Co. Incidence of micronutrient deficien- cies in crops has increased markedly in recent years due to intensive cropping, loss of top soil by erosion, losses of micronutrients through leaching, liming of acid soils, decreased proportions of farmyard manure compared with chemical fertilizers, increased purity of chemical fertili- zers, and use of marginal lands for crop production. Micronutrient deficiency problems are also aggravated by high demand of modern crop cultivars. Plant acquisition of micro- nutrients is affected by numerous soil, plant, microbial, and environmental factors. Factors such as pH, redox potential, biological activity, SOM, cation exchange capacity, and clay contents are important in determining availability of micronutrients in soils. Plant factors such as root and root hair morphology (length, density, surface area), root induced changes (secretion of H+, OH-, HCO3-), root exudation of organic acids (citric, malic, tartaric, oxalic, phenolic), sugars, and non-proteinogenic amino acids (phytosiderophores), secretion of enzymes (phosphatases), plant demand, plant species/ cultivars, and microbial associations (enhanced CO2 production, rhizobia, mycorrhizae, rhizobacteria) have profound influences on plant ability to absorb and utilize micronutrients from soil.The objectives of this article are to report advances in research on micro- nutrient availability and requirements for crops, in correcting deficien- cies and toxicities in soils and plants, and in increasing the ability of plants to acquire needed amounts of micronutrient elements.