Micronutrients: Small But Mighty

Micronutrients: Small But Mighty

The third category of essential crop nutrients is called micronutrients. Plants don’t need as much of them as they do primary and secondary fertilizers, but they still can’t do without them. Scientists classify boron (B), chlorine (Cl), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), nickel (Ni), and zinc (Zn) as essential micronutrients. Of these, boron, copper, zinc, and manganese are most often in short supply for growing crops.

Boron. Boron is essential for healthy cell growth in plants, and is important in the formation of pollen as well. Without pollen, many plants – including most important food and feed crops— would not be able to bear fruit and reproduce. A shortage of boron may also stunt the growth of plants.

The benefits of boron are not limited to plants, either: Some nutritional research indicates boron may have a role in helping prevent osteoporosis.

Chlorine. Chlorine helps plants manage water stress and may help some plants resist fungal diseases. Farmers apply fertilizers containing chlorine typically to small grains like wheat.

Copper. In plants, copper is important mostly as a catalyst (it promotes chemical reactions without becoming part of the product of those reactions). Its indirect role is an important one, though: without it, plants will not develop normally. Copper is also important in the formation of protein pigments found in red blood cells, making it a key micronutrient for animals and humans as well as plants.

Iron. Like copper, iron serves as a catalyst, especially in the formation of chlorophyll. It also helps regulate certain plant enzymes, and promotes root function in legumes. The leaves of plants deficient in iron often turn pale green or even yellow, a signal that the plant isn’t forming chlorophyll properly. Farmers can apply fertilizer containing the proper form and amount of iron either to the soil or the foliage of the crops.
Manganese. Manganese is yet another micronutrient that helps plants synthesize chlorophyll, as well as helping regulate several important plant enzymes. In fact, it performs some of the same functions in humans. Making sure plants have enough manganese in their diets also helps make sure we have enough in ours. Fertilizer products containing manganese include manganese sulfate and manganese chloride.
Molybdenum. Molybdenum helps plants make efficient use of nitrogen and phosphorus. That makes molybdenum important for plants; when there’s enough molybdenum available, the plants are better nourished by primary nutrients. It’s also important for farmers. When the plants make better use of nitrogen and phosphorus, the farmer gets a better return on investment in fertilizer.
Zinc. Zinc plays key roles in human health and nutrition as well as in plants. It helps plants form proteins, starches, and growth hormones, and helps people grow normally and have healthy skin and bones. As with manganese, helping make sure plants have enough zinc helps make sure we have enough, too

Secondary Nutrients: Calcium, Magnesium, and Sulfur

While N, P, and K are the most important of the essential elements for plant nutrition, they are by no means the only important elements. Farmers, scientists, and agricultural professionals generally consider calcium (Ca), magnesium (Mg), and sulfur (S) second in importance only to nitrogen, phosphorus, and potassium, not because they are less essential, but because smaller amounts of those elements are typically needed for most crops.

Liming adds calcium to the soil and raises the pH, which can help crops use nutrients more efficiently.

The light-colored rows are suffering leaf bronzing and yellowing caused by magnesium deficiency.

Calcium. Calcium helps roots and leaves grow strong and healthy. In addition, it helps strengthen overall plant structure, increasing resistance to wind, hail, insects, and other sources of physical damage. Calcium also is an important component of bone, making it a crucial nutrient for animals and humans.
Calcium tends to be plentiful in most soils, but is not always in a form available to plants. Where calcium is deficient, it can be supplied in the form of lime (ground limestone), or it can be mixed with a liquid carrier and sprayed on fruit and foliage of crops. Foliar application is sometimes used on celery, apples, pears, and cherries.
Important commercial calcium fertilizers include ground limestone and gypsum (calcium sulfate), among others

Magnesium. Among its roles in plant growth, magnesium is the central atom in chlorophyll, the molecule responsible for photosynthesis, the process where plants turn sunlight and nutrients into green growth. Most of the magnesium in plants is found in chlorophyll. Like phosphorus, magnesium moves from the older parts of the plant to the younger as the plant grows. Farmers know a crop may be deficient in magnesium when the older leaves turn bronze, yellow, or reddish, while the leaf veins remain green.
Important commercial magnesium fertilizers include limestone, magnesium oxide, magnesium sulfate, potassium-magnesium sulfate, and magnesium chloride.
Sulfur. Sulfur is essential for the production of amino acids, which are the building blocks of proteins found in all living things. Sulfur also helps give crops like onions, mustard, and radishes their characteristic odor.
While it is abundant in soil that is rich in organic matter, sulfur (like other nutrients) is not always available in a form plants can use. Certain crops, such as alfalfa, a forage crop used for animal feed, also remove more sulfur than others.
Commercially important fertilizers containing sulfur include ammonium sulfate, ammonium thiosulfate, potassium sulfate, potassium-magnesium sulfate, gypsum, and magnesium sulfate.