Unit: Plant Nutrition

Nutritional Needs of Plants

Macronutrients:

• Carbon (C)
• Hydrogen (H)
• Oxygen (O)
• Nitrogen (N)
• Phosphorous (P)
• Potassium (K)
• Sulfur (S)
• Calcium (Ca)
• Magnesium (Mg)

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Micronutrients:

• Chlorine (Cl)
• Iron (Fe)
• Manganese (Mn)
• Boron(B)
• Zinc (Z)
• Copper (Cu)
• Molybdenum (Mo)

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Plants and mineral nutrients:

Plants require certain elements in order to grow and stay healthy.

16 Elements essential to plant growth:

What makes an element essential?

There are 3 established criteria for an “essential element”:

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2. Action of the element must be specific- no other element can substitute for it.

3. The element must be directly involved in the nutrition of the plant.

1. The plant cannot complete it’s life cycle without the element.

Macro vs. Micro

• Macronutrients: nutrients required in large amounts and absorbed from the soil or hydroponic solution.

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• Micronutrients: nutrients required in small amounts and absorbed from a soil or a hydroponic solution.

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• Does NOT imply importance. All of the essential nutrients are required for growth and function.

Mobile vs. Immobile

These nutrients are further divided into the mobile and immobile nutrients.

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Mobile: A plant will always supply more nutrients to its younger leaves than its older ones, so when nutrients are mobile, the lack of nutrients is first visible on older leaves.

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Immobile: When a nutrient is less mobile, the younger leaves suffer because the nutrient does not move up to them but stays lower in the older leaves.

Macronutrients

• Carbon (atmosphere)
• Hydrogen (Water)
• Oxygen (atmosphere)

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These 3 nutrients make up 95% of a plants fresh tissue.

Typically not limiting factors except for:

Drought

Disease

Extreme cold

Poor drainage

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N - Nitrogen

• Function: Nitrogen stimulates growth, increase of fruit production and gives plants a healthy green color.

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• Toxicity: dark green plant with restricted root system and fruit set.

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• Deficiency: Mobile. Growth restricted. Leaves become light green and yellow then die.

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K - Potassium:

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• Function:

Catalyst/activator for enzymes

Encourages vigor/health

• Deficiency: Highly mobile – older growth

Poor growth, chlorosis, necrosis; reduced gas exchange

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• Toxicity: Hi K may cause Ca, Mg, Mn, Zn, Fe deficiencies

P - Phosphorus:

• Function: for the energy molecules: ATP, ADP, AMP

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• Deficiency: Very mobile (old growth)

Lower leaf surfaces turn purple

Leaves curl downward

Poor leaf, root, flower development

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• Toxicity: Not usually a problem

Ca -Calcium:

• Function:

As an activator of enzymes

Plant strength & vigor

As a “neutralizing” agent

• Deficiency: Immobile (new growth)

Misshapen, poor or no growth

Blossom end rot of fruit

• Toxicity: Not usually a problem

(Mg) Magnesium:

Function:

“heart” of the chlorophyll molecule

Enzyme activator (ATP, DNA, RNA)

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• Deficiency: Highly mobile

Older leaf interveinal chlorosis

Upturned leaves

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• Toxicity:

Not known

Sulfur:

• Function:

Form “disulfide bonds” that aide in the folding of proteins and effect their function

• Deficiency: Moderately mobile

Less chlorophyll 🡪 chlorosis and

purplish veins in mid/young leaves

Thin, brittle stems

• Toxicity:

Red. Growth, interveinal chlorosis, leaf burn

Let’s review the macros… (all result in poor growth)

Mobile Functions Def. Symptoms

N Y protein, RNA, DNA, Chl chlorosis, necrosis

P Y ATP, etc. purple underleaf

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K Y Catalyst/activator for enzyme red. Transpiration

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Ca N cell walls, enzyme act. poor “new” growth

blossom end rot in fruit

Mg Y Chlorophyll, enzyme act. Interveinal chl.

brittle upturn leaf

S Mod 2 amino acids “mid/new” growth: chlorosis, purple veins, thin brittle stems

Micronutrients:

Iron: (Fe)

• Function:

Involved in chlorophyll & protein synthesis and respiration

• Deficiency: Immobile

New growth interveinal chlorosis

• Toxicity:

If over-apply foliar 🡪 necrotic spots

Manganese: (Mn)

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• Function:

Enzyme activator (chl, RNA, DNA)

carbohydrate metab., O2 prod.

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• Deficiency: Relatively immobile

Newer growth interveinal chlorosis

Necrotic spots/leaf drop

Upward leaf curl

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• Toxicity:

Reduced growth

Hi Mn 🡪 Low Fe and interveinal chlorosis

Boron: (B)

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• Function:

Related to metabolism of Ca, K

Regulates carbohydrate

Involved in RNA synthesis

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• Deficiency: Mobile in leaf; not in plant

Stems: abnormal/slow growth, brittle

Shoot/root die back

Young leaves: thick, curled

Low flowering, fruiting; fruit rots

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• Toxicity:

Def. sym. + leaf tip chlorosis/necrosis

Zinc: (Zn)

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• Function:

Enzyme activator

Synthesis of proteins, hormones,

RNA, DNA

• Deficiency: Not very mobile

Abnormal and stunted growth

Leaves: interveinal chlorosis, necrosis

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• Toxicity:

Similar to def. symp.

Copper: (Cu)

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• Function: (70% of Cu in leaf in chloroplasts)

Chlorophyll synthesis

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• Deficiency: Immobile

Leaf stunting, twisting; dark green

Reduced turgor (firmness)

Reduced flowering/fruiting

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• Toxicity: Do not use Cu tube/fixtures

Overall stunting; thick, dark roots

Molybdenum: (Mo)

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• Function

Involved in carbohydrate metabolism.

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• Deficiency: Mobile

Leaf interveinal chlorosis, mottling, scorching, inward cupping

Severe: puffy leaf areas & stunting

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• Toxicity:

Not usually seen…

Leaves can turn yellow

Chlorine: (Cl)

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• Function:

Enzyme activator

Promotes healthy growth of plants

Hi NaCl 🡪 stress 🡪 flavor, nutrition

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• Deficiency: Mobile

Leaf chlorosis then necrosis

Low transpiration, wilting

Plant stunting, die back

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• Toxicity: Leaf tip burn.

Let’s review the micros:

** Some are mobile, some are not

** ALL are involved in plant metabolism

Enzyme activators

Parts of enzymes

In electron transfer

As oxygen carriers

Invovled in synthesis/metabolism of proteins, hormones, RNA/DNA, carbohydrates, chlorophyll, ion balance, etc.

** KEY: mainly move around assisting in reactions, etc. Therefore, not needed in large amounts for “structure”.

Other nutrients:

Found in some but not all plants; possibly required by those plants

Sodium (Na) C4 plants

Silicon (Si) C4 & CAM

Cobolt (Co) N-fixing bacteria

Vanadium (V) Essential in green algae; toxic in hp in hi conc

Iodine (I) Stimulates growth in low conc; toxic in hi conc

Bromine (Br) Can substitute for Cl

Fluorine (F) Toxic; some plants accumulate; hi in teas!

Aluminum (Al) Req’d for tea bush; toxic for most plants

Nickel (Ni) Maybe req’d for N-fixers; toxic for other plants

Selinium (Se) In milk vetches; toxic to most plants