SS221 Macronutrients Lect

Sulfur Classification

Secondary macronutrient.

Sulfur Plant Available Form

SO4²⁻ (sulfate).

Sulfur Soil Mobility

Mobile (more than phosphate, less than nitrate).

Sulfur Plant Mobility

Immobile in plant (deficiency in new growth).

Sulfur % in Tissue

0.15–0.45% of foliage.

Sulfur Uptake Form

Roots absorb SO4²⁻ only.

Sulfur Amino Acids

Cysteine and methionine.

Sulfur Main Function

Protein synthesis and enzyme activation.

Sulfur Flavor Role

Forms compounds in garlic, mustard, onions.

Sulfur High Demand Crops

Legumes, brassicas, onions.

Sulfur Deficiency Symptom

Yellowing in new leaves.

Sulfur vs Nitrogen Deficiency

S in new growth; N in old growth.

Sulfur Deficiency Soils

Sandy, low CEC, low SOM soils.

Sulfur Oxidation

H2S or elemental S → SO4²⁻.

Sulfur Reduction

SO4²⁻ → S²⁻ in anaerobic soils.

Hydrogen Sulfide Indicator

Rotten egg smell.

Sulfur Main Soil Pool (Humid Regions)

90–98% in organic matter.

Sulfur Mineralization Control

Controlled by C:S ratio.

Critical C:S Ratio

300–400 causes immobilization.

Sulfur Subsoil Mineral

Gypsum (CaSO4·2H2O).

Sulfur Reduced Mineral

Pyrite (FeS2).

Sulfur Atmospheric Source

SO2 deposition and dust.

Sulfur Deposition Trend

Declining since 1990.

Sulfur Fertilizers

Elemental S, gypsum, ammonium sulfate.Calcium Plant Available Form

Calcium Soil Mobility

Slightly mobile.

Calcium Plant Mobility

Immobile.

Calcium % in Plants

0.1–5%.

Calcium Main Function

Cell wall structure and plant stiffness.

Calcium Growth Role

Stimulates root and leaf development.

Calcium Nitrogen Role

Helps reduce NO3⁻

Calcium in N Fixation

Required by N

Calcium Deficiency Location

Young tissue and fruits.

Calcium Deficiency Symptom (Monocots)

Young leaves stick and fail to unfold.

Calcium Deficiency Symptom (Tomato)

Blossom end rot.

Blossom End Rot Cause

Poor Ca transport due to irregular watering.

Calcium Soil Pools

Minerals, organic matter complexes, CEC sites.

Calcium and pH

Low in acid soils; high in base

Calcium at High pH (>7.2)

Forms insoluble P compounds.

Calcium and CEC

High CEC soils hold more Ca²⁺.

Calcium Competition

High other cations reduce uptake.

Calcium Parent Material

Limestone high Ca; sandstone low Ca.

Calcium Transport

Moves via xylem with transpiration.

Calcium and Soil Structure

Promotes flocculation and aggregation.

Magnesium Plant Available Form

Mg²⁺.

Magnesium Soil Mobility

Immobile (held on CEC).

Magnesium Plant Mobility

Mobile (deficiency in old leaves).

Magnesium Main Function

Central atom in chlorophyll.

Magnesium % in Chlorophyll

15–20% of plant Mg.

Magnesium Ribosome Role

Structural component for protein synthesis.

Magnesium ATP Role

Regulates phosphate transfer in ATP.

Magnesium Enzyme Role

Activates enzymes.

Magnesium Deficiency Symptom

Interveinal chlorosis in older leaves.

Magnesium Competition

High K reduces Mg uptake.

Grass Tetany Cause

High K:Mg ratio in forage.

Grass Tetany Conditions

Cool soils with moderate/high K.

Magnesium Soil Sources

Dolomite, biotite, hornblende, serpentinite.

Ideal Ca:Mg Ratio

Ca 60–90%; Mg 5–20% of CEC.

Serpentine Soil Ca:Mg Ratio

0.1–0.5 (very low).

Sulfur Summary

SO4²⁻; mobile in soil; immobile in plant; deficiency in new growth; best available pH 5–7.

Calcium Summary

Ca²⁺; slightly mobile in soil; immobile in plant; cell walls; deficiency in young tissue; best at neutral pH.

Magnesium Summary

Mg²⁺; immobile in soil; mobile in plant; chlorophyll component; deficiency in old leaves; best pH 6–7.5.

Micronutrient Requirement

Needed in very small amounts.

Micronutrient Toxicity Range

Small gap between deficiency and toxicity.

High pH Effect

Decreases most micronutrient availability except Mo.

Sandy Soil Risk

More prone to micronutrient deficiency.

Flooded Soil Effect

Increases Fe²⁺ availability.

Chelates

Improve micronutrient availability in high pH soils.

Boron Available Forms

BO3²⁻, B4O7²⁻, B(OH)3.

Boron Soil Mobility

Mobile.

Boron pH Range

5–7.5.

Boron Function

Flower formation and fruit set.

Boron Toxicity Risk

Poor drainage or low

Copper Available Form

Cu²⁺.

Copper pH Range

5–7.

Copper Binding

Tightly bound to organic matter.

Copper Deficiency Soil

High OM soils (>8%).

Copper Toxicity Source

Manure or Cu pesticides.

Iron Available Forms

Fe²⁺ and Fe³⁺.

Iron Most Available Form

Fe²⁺ (reduced).

Iron pH Range

4–6.5.

Iron Function

Chlorophyll formation and redox reactions.

Flooding Effect

Reduces Fe³⁺ to Fe²⁺ increasing availability.

Manganese Available Form

Mn²⁺.

Manganese pH Range

5–6.5.

Manganese Function

Photosynthesis and nitrogen metabolism.

Manganese Deficiency

Common in high pH soils.

Molybdenum Available Form

MoO4²⁻.

Molybdenum pH Range

7–8.5.

Molybdenum Unique Trend

More available at high pH.

Molybdenum Animal Risk

Can induce copper deficiency in livestock.

Zinc Available Form

Zn²⁺.

Zinc pH Range

5–7.

Zinc Human Importance

30% of global diets deficient.

Nickel Available Form

Ni²⁺.

Nickel pH Range

5–7.

Nickel Deficiency Crop

Pecan (mouse ear).

Chloride Available Form

Cl⁻.

Chloride Mobility

Highly mobile.

Chloride pH Effect

Not affected by pH.

Chloride Function

Photosynthesis and enzyme activation.