Lecture 22: Mineral Nutrition - 11/29 Flashcards
What additive do high agricultural yields depend on?
High agricultural yields depend on fertilization with mineral nutrients
How are yields affected by addition of fertilizer?
For most crops, yields increase linearly until a plateau with the amount of fertilizer they absorb
What has happened to world consumption of the primary mineral elements (NPK) over time?
It has climbed, from 30 million metric tons in 1960 to over 200 million metric tons currently
About how much energy does the production, distribution, and application of nitrogen fertilizers take up in agriculture?
Over half
What are the 6 macronutrients?
Nitrogen
Phosphorus
Potassium
Calcium
Magnesium
Sulfur
Micronutrients (also known as trace/minor elements)
Necessary for plants in very small quantities
What is the NH4+ (ammonium) to NO3- (nitrate) balance determined by?
pH
Cation Exchange Capacity (CEC)
The ability of soil to retain, attract, and exchange cations
Are cations or anions susceptible to water leaching?
Cations are not susceptible to water leaching, whereas anions are
Nitrogen
A vital component of amino acids and nucleic acids.
The most frequently deficient element in crop production
Too much nitrogen can cause excessive vegetative growth and delay flowering/fruiting
Atmospheric nitrogen
Not available to plants until it is fixed
Different forms of nitrogen
Nitrogen gas (N2), ammonia (NH3), ammonium (NH4+), nitrate (NO3-), nitrite (NO2-), organic nitrogen (various compounds such as amino acids)
Organic nitrogen must undergo mineralization before it is accessible to plants
Mineralization
The process by which chemicals present in organic matter are decomposed or oxidized into easily available forms to plants
Which forms of nitrogen are available to plants?
Ammonium (NH4+) and nitrate (NO3-)
Nitrification
A microbial process by which compounds are oxidized to nitrite and nitrate. Most effective in neutral soils
What are some problems associated with nitrification?
1) NO3- is easily leached
2) anaerobic bacteria in waterlogged soils can cause denitrification
3) nitrification bacteria are less abundant in acidic soils
Industrial fixation
Synthesis of ammonia from atmospheric N2
What are the relative proportions of the processes that result in the natural fixation of nitrogen?
~10% comes from lightning and photochemical reactions
~90% comes from biological fixation
How does symbiotic N fixation occur?
Bacteria associate with plant roots by forming nodules, providing them with nitrogen in exchange for carbohydrates
What is one genus of symbiotic bacteria that helps fix nitrogen?
Rhizobium
Nitrogenase
An enzyme that carries out the reduction of nitrogen to ammonia, which is immediately converted to ammonium
To do this, a large amount of energy is required
What does nitrogenase need to function?
An anaerobic environment
Phosphorus (P)
Needed in compounds involved in energy storage, membranes, and DNA/RNA
Only a small amount of P is available to a plant at a given time
Potassium (K)
Helps regulate osmotic pressure and activates many enzymes involved in photosynthesis and respiration
Soils contain more K than N/P, but it is in relatively unavailable forms
Calcium (Ca)
Role in cell walls and in signal transduction cascades
Magnesium (Mg)
Part of the chlorophyll molecule and activates some enzymes in photosynthesis and respiration
Sulfur (S)
Part of some amino acids and pungent compounds
Can be used as a fungicide
Iron (Fe)
Involved in respiration and photosynthesis (in electron transport systems)
The availability of this micronutrient depends on soil pH
