micronutrients section n soil fertility and plant nutrition

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Micronutrients Section N Soil Fertility and Plant Nutrition

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Page 1: Micronutrients Section N Soil Fertility and Plant Nutrition

MicronutrientsSection N

Soil Fertility and Plant Nutrition

Page 2: Micronutrients Section N Soil Fertility and Plant Nutrition
Page 3: Micronutrients Section N Soil Fertility and Plant Nutrition

Micronutrients in Plants• Transition metal micronutrients:

Fe, Mn, Zn, Cu, Mo, Ni - are important as enzyme cofactors, metal components of enzymes, and in electron transfer reactions. Immobile in plants.

• Non-metal micronutrientsB - important for cell division,

meristematic tissue. Immobile in most plants.

Cl - important for osmotic regulation. Mobile in plants.

Page 4: Micronutrients Section N Soil Fertility and Plant Nutrition

Micronutrient Mobility

• In plants:– With the exception of Cl, all

micronutrients are immobile in plants. However, remember about B?

– Significance?• In soils:

– All except Cl are immobile in most soils.

Page 5: Micronutrients Section N Soil Fertility and Plant Nutrition

Deficiencies

Mn - pecan

Mn - lemon

Page 6: Micronutrients Section N Soil Fertility and Plant Nutrition

Manganese• Manganese activates many enzymes

including metabolism, energy transport and fatty acid synthesis.

Page 7: Micronutrients Section N Soil Fertility and Plant Nutrition

Deficiencies

Zn - corn

Zn - citrus

Zn - pecan

Page 8: Micronutrients Section N Soil Fertility and Plant Nutrition

Zinc• Zinc as manganese activates many

enzymes. It is also essential for synthesis of auxin, a key hormone controlling cell growth.

Page 9: Micronutrients Section N Soil Fertility and Plant Nutrition

Iron• Iron plays a function in

photosynthesis.

Page 10: Micronutrients Section N Soil Fertility and Plant Nutrition

Deficiencies

Fe - beans

Fe - peanuts

Page 12: Micronutrients Section N Soil Fertility and Plant Nutrition

Boron• The function of boron in plants is not

well understood. It is involved in carbohydrate transport, and cell membrane and cell wall development

Page 13: Micronutrients Section N Soil Fertility and Plant Nutrition

Deficiencies

B - alfalfaB-canola

B - cauliflower

Page 14: Micronutrients Section N Soil Fertility and Plant Nutrition

Micronutrients in Soils• Transition metals

– occur mostly in primary and secondary minerals. Fe is the most abundant. Abundance of Fe increases as soils weather. Zn deficiency is the most widespread of micronutrient deficiencies.

• B– Occurs in SOM (50%) and in minerals such

as borates. Is most common in arid soils.• Cl

– Most abundant in arid soils and near coasts

Page 15: Micronutrients Section N Soil Fertility and Plant Nutrition

Incidence of Zn Deficiency

http://www.iza.com

Page 16: Micronutrients Section N Soil Fertility and Plant Nutrition

Chemical Availability

• Available Nutrient forms Cl Cl-

B H3BO3

Mo MoO42-

Fe Fe2+, Fe3+

Mn Mn2+, Mn3+

Zn Zn2+

Cu Cu2+, Cu+

Page 17: Micronutrients Section N Soil Fertility and Plant Nutrition

Availability• Most important factors influencing

availability of micronutrients:Soil texture (clay content)Degree of soil weatheringpH - most important Redox potential (aerobic vs. anaerobic). Fe, Mn, Cu much more available under anaerobic conditions.

Page 18: Micronutrients Section N Soil Fertility and Plant Nutrition

pH

Relative N

utrient Availability

pH and Nutrient Availability

Fe, Mn, Cu, ZnReason: Solubilityof minerals

MoReason: AnionAdsorption

ClReason: Usually leached from acidsoils

BReason: leachedfrom acid soils.Chemically unavailablein alkaline soils

5.0 7.0

Page 19: Micronutrients Section N Soil Fertility and Plant Nutrition
Page 20: Micronutrients Section N Soil Fertility and Plant Nutrition

Effects of Redox on Availability

• Availability of Fe, Mn, Cu are directly affected by redox– Under anaerobic conditions, Fe, Mn, and Cu

become more availability– Can become toxic, particularly Mn

Mn toxicity

Page 21: Micronutrients Section N Soil Fertility and Plant Nutrition

Deficiencies of Micronutrients• Conditions most likely to result in

deficiencies of:– Fe, Mn, Cu, Zn, Ni:

• Weathered, sandy soils.• Alkaline, aerobic soils. Cu deficiency likely in

organic soil

– Mo• Weathered, acid soils and sandy soils

– B• Weathered, acid soils and sandy soils

– Cl• Weathered, acid soils far from seacoasts

Page 22: Micronutrients Section N Soil Fertility and Plant Nutrition
Page 23: Micronutrients Section N Soil Fertility and Plant Nutrition

Differences Among Plants

• Some plants are adapted to conditions of low micronutrient availability and rarely suffer deficiency:– Ability to change the rhizosphere pH and

redox to increase nutrient availability.

– e.g. some roots secrete enzymes called phytosiderophores to increase Fe availability.

Page 24: Micronutrients Section N Soil Fertility and Plant Nutrition

Fertilizing with Micronutrients

• In alkaline soils, Fe, Mn, Cu, and Zn may react readily with soil constituents, rendering them insoluble and unavailable.

– Therefore, use either chelated nutrients for soil application, or foliar applications of salt solutions.

– B - use borate materials. Over-fertilization with B can cause toxicities

– Cl - fertilizers are rarely used

Page 25: Micronutrients Section N Soil Fertility and Plant Nutrition

Chelated (EDDHA)-Fe

Page 26: Micronutrients Section N Soil Fertility and Plant Nutrition

Fe-EDTA

FeN

NO

O CH2

CH2

CO CH2

CO CH2

OCO

CH2

OCO

CH2

Chelated IronFe -EDTA

Page 27: Micronutrients Section N Soil Fertility and Plant Nutrition

• Applying Fe fertilizer to an alkaline soil:Fe3+ + 3 OH- FeOOH + H2O

Applying Fe chelate to an alkaline soil:

Fe-Ch + 3 OH- FeOOH + Ch3- + H2O

Chelate Mode of Action

(available)

(available)

(unavailable)

(unavailable)

Page 28: Micronutrients Section N Soil Fertility and Plant Nutrition

Micronutrients• Threshold between deficiency and

toxicity narrow.• Efficiency of utilization for metal

micronutrients a challenge due to soil reaction.

• Often used where not needed.• Periodically needed and not used.• Fine tuning required in most areas

substantial research required in a few.

Page 29: Micronutrients Section N Soil Fertility and Plant Nutrition

Summary - Micronutrients • Most important factors influencing

micronutrient availability in soils:– pH, redox, weathering, texture

• Most micronutrients are immobile in soils and plants– Diagnosis, treatment

• Metal micronutrients are normally applied as chelates or byfoliar application.