Plant Nutrition 101 #6

Metal Micro- nutrients

By Riley Holly

So far the Primary and macronutrients have been addressed. While the micronutrient requirements of most plants are much less, and in most soils are abundant, they are still necessary for successful plant growth. Sometimes there are deficiencies and those elements need to be replenished.

These micronutrients often become depleted when plant materials containing the elements are discarded, rather than worked back into the soil. This is another reason for composting, thus returning the elements to the soil.

The micronutrients can be classified into two groups: The metals (positive ions cations) Cu, Fe, Mn, Ni, & Zn. and the negatively charged or neutral nutrients, (B, Cl, Mo).

The first group (metals) are similar as to how they react in the soil. Even though these metals are present in the soil, most are not readily available to the plant, as they are bound tightly to the soil surface. The plant takes up the metals as positive-two ions (e.g. Cu++).

Copper is immobile in the plant and symptoms show up in the new growth. Excess copper can be highly toxic and it should not be added to the soil unless the need is established.

Copper deficiency symptoms are:

* Stunted growth

* Dieback in terminal shoots

* Wilting & necrosis of leaf tips

* Poor pigmentation (blue-green leaves)

* Loss of turgor

Excess symptoms are:

* Reduced growth, necrosis

Iron is essential in photosynthesis, chlorophyll synthesis, and cell division. It is commonly deficient in Western soils that have a pH greater than 7.0. It is not mobile in plants and the symptoms occur in the young leaves. Deficiency symptoms are:

* Interveinal chlorosis of young leaves (green veins)

* Twig dieback

* Reduced growth

* Stems slender

* Defoliation & twig dieback

* Symptoms similar to manganese deficiency

Manganese is an activator for enzymes in plant growth, and is a catalyst with Iron in chlorophyll synthesis. It is mobile in the soil but only slightly mobile in plants.

Deficiency symptoms are:

* Interveinal, marginal chlorosis of young leaves

* Interveinal necrotic spots

* No sharp distinction with veins

* Curled leaf margins

* Similar to Fe deficiencies

Excess symptoms are:

* May induce Fe deficiency

* Loss of foliage color, bronzing of leaf margins

* Necrotic areas

Nickel is important for nitrogen metabolism and is a recent addition to the list of plant nutrients. Nickel is immobile in plants. Deficiency symptoms (under research conditions) can be:

* Leaf tip chlorosis

* Death of the meristem

Excess symptoms

* Induces Fe & Zn deficiencies

Zinc is an essential component of the plants enzyme systems. It

controls the synthesis of indole-acetic acid (IAA), and has a role in chlorophyll synthesis. It is less available at cool temperatures, and is marginally mobile in plants. Western soils (pH > 7.0) are usually deficient.

Deficiency symptoms are:

* Reduced fruit bud formation

* Interveinal chlorosis on young leaves

* Decrease in stem length & rosetteing (witches’ broom) of terminal leaves

* Twig dieback after first year

* Smaller inter-nodal spacing

Excess symptoms are:

* Rapid necrosis