Plant Residue +
Portions of crops that aren’t harvested contain micronutrients as well as the macronutrients. Micronutrients in plant residues become available as the residues are decomposed by soil organisms.
Mineral Fertilizers +
Small quantities of micronutrients are essential for plant growth. They include Cl, Fe, Mn, Zn, B, Cu, Ni, and Mo. When deficiencies are identified by soil or plant testing, these elements can be supplied by fertilizers added to the soil or applied to the plant as foliar treatments. Fertilizers should be in water-soluble form for best results.
Crop Harvest -
Crop removal is the amount of micronutrients removed from the field in harvested portions of the crop. Use our nutrient removal calculator to find out how much micronutrients you should be replacing. Replacement values may not reflect the total amount needed to be applied as fertilizer, because some portion of applied micronutrient fertilizers typically gets fixed in unavailable forms.
Runoff/Erosion -
Runoff is water that is not absorbed into the soil. Erosion is the physical wearing away of the soil through rain, irrigation, wind, and ice. Runoff and erosion can result in lost nutrients, including micronutrients, from the soil. Runoff and erosion can be minimized by maintaining soil cover with crop residue and/or cover crops.
Plant Uptake -
In the soil, plant-available micronutrients are dissolved in the soil solution or adsorbed on soil cation exchange sites. Plant roots absorb micronutrients from the soil solution. As with other nutrients, micronutrient elements must be converted to simple soluble salts in soil solution to become plant-available.
Soil Organic Matter
Organic matter is an important source of micronutrients for the plants. The organic matter can come from plant residue, living organisms, fertilizers, and animal manures. Mineralization of organic matter, also described as decomposition, can replenish dissolved micronutrients in the soil solution. The reverse of mineralization is immobilization – converting inorganic compounds to unavailable organic compounds.
Dissolved micronutrients
Plants absorb dissolved micronutrients from the soil solution. Uptake occurs primarily by diffusion through the soil solution. The micronutrients are needed in small quantities, yet they are still essential to normal plant health and growth.
Clay, Fe/Al Oxides, O.M.
Clay is a natural mineral particle of very small size and specific chemical properties. Iron and aluminum oxides are natural soil minerals and may compose much of the clay fraction in highly weathered soils. Clay, oxides, and portions of soil organic matter may have high negative charge and adsorb dissolved metal cations on what is known as cation exchange sites.
Micronutrient Minerals
Minerals in the soil can affect micronutrient availability. Micronutrient metals (zinc, manganese, copper, iron, nickel) react readily with soil minerals to form precipitated forms not available to plants, such as oxides, carbonates, hydroxides, and phosphates. Most of the total micronutrients in the soil occur in insoluble minerals or organic material. These minerals can slowly dissolve in certain environmental conditions to release micronutrient elements into the soil solution.