Plant Nutrition:
Secondary and Micronutrients

Basic Concepts of Soil Fertility

ü16 essential elements for plant growth

üCHO

üMacro / secondary nutrients (dated term)

ü N, P, K, - Ca, Mg, S

üMicronutrients:

ü Cl, Mn, Fe, Mo, Zn, B, and Cu

üForms available to plants

Plant Nutrient Composition

Forms available to Plants

Ø Ions are charged molecules

^Ø Most plant nutrients are ions (+ / -)

Ø Cations - positively charged ions (Ca⁺⁺)

Ø Anions - negatively charged ions (NO₃^-)

Ø Uncharged molecules (H₃BO₃)

How Plants Absorb Nutrients

ØThrough leaves (foliar) or through soil

ØHigh nutrient demand - soil

Ø active uptake of specific nutrients

ØMicronutrients can be foliarly applied

Ø mechanism is primarily diffusion

Ø good quick fix methods in greenhouses etc.

ØMost soil nutrients enter through roots

Secondary Nutrient Form

Secondary Nutrient Mobility

o Calcium: Most immobile nutrient in plants

o deficiency seen in newest tissue

o Magnesium: somewhat mobile in plants

o deficiency in newer plant parts

o Sulfur: mobile in plants

o less redistribution than N - overall chlorosis

Roles in Plant Nutrition

üN, P, and K covered in detail

üCalcium

^ü membrane integrity - blossom end rot

üMagnesium

ü role in photosynthesis - interveinal chlorosis

üSulfur

ü role in amino acids - flavor - general yellowing

Supplemented to Plants

üSecondary nutrient sources:

üCa, Mg - lime applications

üS - some P fertilizer forms

üManure - some S

üAcid rain - some S

Micronutrient Form Function

Micronutrient Form Function

Micronutrients in Plant Nutrition

üPerform enzymatic functions in plants

üZn, Mn, Cu, Fe - photosynthesis

üB - sugar formation translocation

üMo - nitrate reductase (legumes)

üCl - ionic buffer in plants

Micronutrient Mobility

ØIron: Not mobile in plants

ØCopper: not mobile in plants

ØManganese: not mobile in plants

ØBoron, Zinc, and Molybdenum - not mobile

ØWhere do you expect to see deficiency?

Supplemented to Plants

üMicronutrients:

à Chelated forms

• cationic micronutrients

à Frits (molten glass formulations

• cheaper - all but chloride

à Starter fertilizer

à Foliar application in cases of deficiency

Micronutrient Availability

üpH effect:

ü increased availability with low pH

üException to the rule: Mo

üMicronutrient toxicity - reduced by liming

*Even in its earliest stages, zinc deficiency lowers yield, reduces tree vigor and makes fruit small and poor in quality. Leaf symptoms include small, narrow leaves (little leaf) and whitish-yellow areas between the veins (mottle leaf). Leaves also crowd along short stems (rosetting), and smaller twigs die back. Symptoms are often more pronounced on the northern (sunny) side of the tree.

*N -- general, uniform yellowing or fading of oldest leaves first. No pattern to it.

*P -- never (?) seen in citrus, but on other plants, purplish or reddish pigment forms in the oldest leaves first. The deficiency does certainly occur in citrus; they just don't show good symptoms.

*K -- Seldom seen in citrus. Oldest leaves die back, starting at the tip and along the distal margins. Looks rather like salt burn, but is uniquely on the oldest foliage.

*S -- much like N, general yellowing, but always starts with the newest foliage first.

*Ca -- No good leaf symptoms in citrus

*Mg -- Always on the oldest leaves first. Bottom center of the leaf is green, and the end and sides are yellow or orange, making an inverted "v" or "Christmas tree" shape to the green part, as it zigzags with the veins.

*Fe -- Newest leaves first. Yellowing of the leaf, but the veins remain green. No green borders around the veins; only the veins themselves remain green.

*Mn -- like Iron, newest leaves first. Yellowed leaf, green veins, WITH green borders beside the veins, so the green strip is broader than that of Fe. Leaves grow to be normal size.

*Zn -- like Manganese in all ways (yellow leaf, green veins with green borders, always newest leaves), but the leaf is dwarfed.

*Cu -- big, wrinkly, deep blue-green leaves which look like they are made of cheap plastic. Stems bend down strangely, and develop blisters which eventually burst, bleeding gummy sap.

*B -- no leaf symptoms, but the albedo (white part of the fruit peel) develops brown or grey, dying spots.

*Mo -- Leaves develop bright yellow, circular spots about 1/8-1/4" across. Rare.

*Mg---symptoms generally start with mottled chlorotic areas developing in the interveinal tissue. The interveinal laminae tissue tends to expand proportionately more than the other leaf tissues, producing a raised puckered surface,

*Mn---As the stress increases, the leaves take on a gray metallic sheen and develop dark freckled and necrotic areas along the veins. A purplish luster may also develop on the upper surface of the leaves.

*Mo--An early symptom for molybdenum deficiency is a general overall chlorosis, similar to the symptom for nitrogen deficiency but generally without the reddish coloration on the undersides of the leaves.

*N--Under nitrogen deficiency, the older mature leaves gradually change from their normal characteristic green appearance to a much paler green. As the deficiency progresses these older leaves become uniformly yellow (chlorotic). Leaves approach a yellowish white color under extreme deficiency.

*P- A major visual symptom is that the plants are dwarfed or stunted.

*S-The visual symptoms of sulfur deficiency are very similar to the chlorosis found in nitrogen deficiency. However, in sulfur deficiency the yellowing is much more uniform over the entire plant including young leaves. With advanced sulfur deficiency brown lesions and/or necrotic spots often develop along the petiole, and the leaves tend to become more erect and often twisted and brittle.

*Zn--the early stages of zinc deficiency the younger leaves become yellow and pitting develops in the interveinal upper surfaces of the mature leaves.

*B--These boron-deficient leaves show a light general chlorosis.

*Ca--these symptoms show soft dead necrotic tissue at rapidly growing areas, which is generally related to poor translocation of calcium to the tissue rather than a low external supply of calcium

*Cl--These leaves have abnormal shapes, with distinct interveinal chlorosis. The most common symptoms of chlorine deficiency are chlorosis and wilting of the young leaves

*Cu--These copper-deficient leaves are curled, and their petioles bend downward. Copper deficiency may be expressed as a light overall chlorosis along with the permanent loss of turgor in the young leaves. Recently matured leaves show netted, green veining with areas bleaching to a whitish gray. Some leaves develop sunken necrotic spots and have a tendency to bend downward

*Fe--These iron-deficient leaves (show strong chlorosis at the base of the leaves with some green netting. This distinct venial re-greening observed during iron recovery is probably the most recognizable symptom in all of classical plant nutrition.

2. Nutrient uptake: Mycorrhizae

2. Nutrient uptake

2. Nutrient uptake

4. Plant nutrient use

Attractively simple, but…

Microbial growth efficiency differs

* Among microbe taxa

* With temperature and moisture

* With different substrates