Plant Nutrition and SoilsChapter 29

Plant Nutrition

• Plant Nutrition- uptake from the environment of all raw materials required for essential biochemical processes.

• More than 60 elements have been identified in plants.

• 1880s- ten chemical elements were designated as essential for plant growth.– Carbon, hydrogen, oxygen, potassium, calcium,

magnesium, nitrogen, phosphorus, sulfur, iron.• 1900s- manganese, zinc, copper, chlorine, boron,

molybdenum, and finally nickel.

17 Essential Elements

Essential Elements

Three criteria are used to judge essentiality1) If it is needed for the plant to complete its life

cycle.

2) If it is part of any molecule or constituent of the plant that is itself essential. a) Magnesium in chlorophyll molecule.

b) Nitrogen in proteins.

3) If deficiency symptoms appear in the absence of the element.

2 Types of Essential Elements

• Macronutrients- required in large amounts.– 1000 mg/kg or > of dry matter.

• Micronutrients (trace elements)- required in very small amounts. – 100 mg/kg of dry matter.

Certain plants contain unusually high and low amounts of specific elements.

Silicon

Macronutrient Functions

• Sulfur- amino acids and coenzyme A.• Phosphorus- ATP, nucleic acids, phospholipids.• Magnesium- chlorophyll molecule.• Calcium- cell walls, cofactors, cellular

membrane.• Potassium- osmosis and ionic balance, stomatal

activity.• Nitrogen- amino acids, proteins, nucleotides,

nucleic acids, chlorophylls.• Oxygen, Carbon, and Hydrogen- almost all

chemical molecules, 96% of the plant.

Micronutrient Functions

• Molybdenum- nitrogen fixation and nitrate reduction.• Nickel- enzyme functioning in nitrogen metabolism.• Copper- involved in some REDOX reactions. • Zinc- activator or component of many enzymes.• Manganese- enzyme activator, membrane integrity,

oxygen release in PSN.• Boron- Ca2+ utilization, nucleic acid synthesis, membrane

integrity.• Iron- chlorophyll synthesis.• Chlorine- osmosis and ionic balance.

Global Nitrogen and Phosphorus Use

Nitrogen Losses

~ 1500 lbs/day

or $500/day!

Asynchrony Between N Supply and Demand

Source: G. Philip Robertson IN Ecology in Agriculture, L.E. Jackson, ed.

NUISANCE ALGAE BLOOMS

Eutrophication – Lake Tahoe story

Data courtesy of C.R. goldman and J.E. Reuter, Tahoe Reesrach Group, U. of California-Davis,

http://www.news.ucdavis.edu/tahoetv/

Soil

• Soil- primary nutrient (inorganic ions), water, suitable gaseous environment, and support medium for plants.– Provides a chemical and physical environment

for plant growth.– Minerals- naturally occuring inorganic

compounds that are usually composed of two or more elements. i.e.- Quartz (SiO2), Calcite (CaCO3).

Soil Layers (Horizons)

• Soils consists of at least 3 horizons (layers)

A Horizon= topsoil.

B Horizon= subsoil.

C Horizon= soil base.

Bedrock= below the horizon.

Soils Are Composed of Solid Matter and Pore Space

• Solid Matter- fragments of rock and minerals in the soil.

Coarse Sand 200-2000 µmFine Sand 20-200 µmSilt 2-20 µmClay < 2 µm

• Pore Space- the space around the soil particles.– Air– Water

Plant Pathology- bacteria

Plant Pathology- viruses

Plant Pathology- fungi