Micronutrients for Mississippi Crop Production

With the current commodity prices, some suggest that the 2011 crop be ‘insured’ by applying micronutrients. Is this good policy for Mississippi field crops?

These essential elements are required by plants in very small amounts: boron, zinc, molybdenum, iron, manganese, copper, chlorine, and nickel. Most are sufficient for optimal crop production without supplemental fertilization in Mississippi.

Soil acidity is the important variable:

Micronutrient availability is greatly influenced by soil pH. As pH increases from 4 to 7, zinc, iron, manganese, copper, and boron decrease in solubility and availability, while solubility and availability of molybdenum increases. When soil is in the pH range of 6.0 to 6.5, most micro nutrients are moderately available in soil solution for uptake by plants.

On severely acid soils (pH below 5.0), manganese (and aluminum) are quite soluble and are often taken into plants in toxic amounts. Conversely, molybdenum is insoluble, and deficiencies often occur in these low pH soils. At a pH of 5.0 to 5.5, certain plants may exhibit problems of manganese toxicity and molybdenum deficiency.

Soil pH values over 7.0, as occurs sometimes from over-liming, or naturally, as in some Blackland Prairie soils, reduces the availability of boron, zinc, iron, and manganese. Deficiencies may occur in these situations. The deficiencies are more likely to be present in early spring under cool, wet conditions.

Boron (B)

Boron is important in many plant processes, including protein synthesis, translocation of sugars and nutrients, respiration, and metabolism of plant hormones.

Boron is leached from soils and is more likely to be deficient under dry conditions on low exchange capacity, well-limed soils. Deficiency symptoms include chlorosis of young leaves, death of the terminal buds and initiation of secondary lateral buds. In cotton, plants are stunted, fruiting is reduced, leaves stay green, and plants remain vegetative past normal time of maturity and senescence. Dark rings appear on leaf petioles, and some leaves may become deformed.

Many clients saw induced boron deficiency on a cotton plant during the Row Crops Short Course last December for the first time.

Boron recommendations for Mississippi are 0.3 to 0.5Ibs/A for cotton and 0.5 lb/A on peanuts outside the Delta. Excessive rates of boron can be toxic to seeds or seedlings. Damage to stands can occur at fairly low rates, especially when banded near the seed drill.

Zinc (Zn)

Zinc is important in several plant enzyme systems for protein synthesis and energy production, among other plant processes.

Zinc deficiencies may occur on well-limed, sandy-loam soils outside the Delta. Corn often shows zinc deficiency symptoms which include interveinal chlorosis, particularly between the margin and midrib which produces a striping effect. Plants will be stunted due to the major role of zinc in internode elongation. Stunting, resetting, and pale green leaves are typical deficiency symptoms in pecans. If needed, two to three pounds can be provided to corn outside the Delta. It may be needed on high pH soils in the Delta.

Molybdenum (Mo)

Molybdenum is vital in nitrogen assimilation such as transforming nitrate nitrogen to protein nitrogen. It is necessary for nitrogen-fixation in legumes by Rhizobia bacteria, sulfur metabolism, phytohormone biosynthesis, and stress reactions.

Molybdenum is recommended for soybeans on Delta soils with a pH of 5.5 or below, and elsewhere on all soils except for the high pH soils of the Blackland Prairie. A seed treatment with ½ ounce sodium molybdate per bushel of planting seed is recommended. A foliar treatment with 1 ounce sodium molybdate per acre at bloom has also been satisfactory. Other legumes may respond to seed treatments with molybdenum. No general recommendation is currently made.

General deficiency symptoms are stunting and pale green color which resemble symptoms of nitrogen deficiency because of molybdenum’s role in nitrogen use by plants. Leaves may be pale, and scorched, cupped, or rolled. The leaves may also appear thick or brittle.

Iron (Fe)

Iron is required for formation of chlorophyll in plant cells. It is essential in plant biochemical processes such as photosynthesis, respiration, symbiotic nitrogen fixation, hormone biosynthesis, and pathogen defense.

Iron deficiency seldom occurs in Mississippi soils which are high in iron content. Deficiency can be induced under conditions of high pH and high manganese content especially under cold, wet conditions when uptake is reduced.

Deficiency symptoms reflect the role in chlorophyll production and include interveinal chlorosis of young leaves with a sharp distinction between the veins and other areas of the leaf.  The entire leaf will become whitish-yellow as the deficiency develops, and then die. Plant growth is slow.

No general recommendations are made, but materials such as iron sulfate, which is soluble, or iron chelates are generally used as a soil or foliar application when specific deficiencies occur.

Manganese (Mn)

Manganese is necessary for plant metabolism and development as either a catalyst or activator. Manganese deficiency has seldom been a problem in Mississippi, but could occur on high-lime, low-exchange capacity soils or other situations. However toxicity is often an issue in acid soils of the state due its increased availability in these conditions. The toxicities are common in cotton and soybeans grown on soils with pH at 5.3 and lower. No recommendations are made at this time.

Copper (Cu)

Copper is essential for photosynthesis, nitrogen and carbon metabolism, and cell wall synthesis. Copper can become toxic in the plant through catalyzing certain reactions that can lend to damage of proteins and other molecules.  However, mechanisms exist in plants to prevent copper from accumulating in a toxic form.

Copper deficiency symptoms are stunting of plants, chlorosis in younger leaves, die back of terminal buds in trees, wilting, delayed maturity, and death of leaf tips. Deficiencies seldom occur in Mississippi. No recommendations are currently made.

Chlorine (Cl)

Choride is a mobile anion in plants, so most of its functions are related to electrical charge balance. It is abundant in most soils, and has been added to many as a component of muriate of potash fertilizer. No deficiency symptoms or need for application of chlorine has been identified in crops grown in Mississippi.

Nickel (Ni)

Nickel was reported as an essential nutrient in the early 1980’s for some enzymes involved in seed germination.

Deficiency symptoms include poor seed germination, and chlorosis and interveinal chlorosis in young leaves that moves to tissue death. Nickel deficiency has not been identified in Mississippi crops.