SWES 200- Ch 12-2

The second most limiting nutrient to plant growth in terrestrial
ecosystems is _______.
Phosphorus is usually the most limiting nutrient in _______ ________ _______.
fresh water
Phosphorus has just one basic chemical form in soil, what is it?
Phosphate, PO43-
Plants use about ___ as much Phosphorus as Nitrogen
Plants use the phosphate ions H2PO4? and HPO42? Distribution between the two forms is controlled by pH, which form is found in high pH and which is found in lower pH?
High pH: HPO42-
Low pH: H2PO4-
Many acidic tropical soils (oxisols) are depleted of Phosphorus
because of P fixation by:
Al and Fe oxides
Soon after addition to soils, much P fertilizer becomes unavailable because of several mechanisms:
– In acid soils, P ions are adsorbed to Fe and Al oxides, or
precipitate with Fe and Al to form insoluble minerals.
– In neutral to alkaline soils, P ions are adsorbed to CaCO3, or
precipitate with Ca to form insoluble Ca phosphates.
Only P in _____ ______ to a plant root is absorbed.
close proximity (~ 2 mm)
Usually no more than 30% of applied P is taken up by plants, why?
because of the reactions with soil
What can be done to maximize P availability?
• Maintain pH at 6 to 7
• Add organic material to soils – this ‘plugs’ up P fixation sites
and reduces soil P?fixing capacity
• Apply P fertilizers in concentrated bands near plant roots
(minimize contact with soil)
Factors Affecting P Availability
• Soil Temperature
– Lower P availability in colder soils (slower P ion movement)
• Soil Moisture
– Higher P availability in flooded soils (more P minerals dissolve
apatite is mined. It is treated with acids to:
form various fertilizers:
– triple superphosphate
– single superphosphate
– ammonium phosphates
Animal manures have __________________ relative to other nutrients
high P concentrations
Phosphorus contamination can cause eutrophication. What is the process of eutrophication?
1. Accelerated growth of algae and water plants
2. Dead plant material decomposes
3. Dissolved O2 is consumed
4. Aquatic life dies from lack
of oxygen
How do you control P Pollution?
• Limit P application
– Limit fertilizer applications to meet plant needs
– Limit manure application rates to soils
• Reduce rates of soil erosion
K?depleted soils include:
• Highly weathered soils
• Acidic soils
Calcium in Plants is what?
– Cell wall component
– aids in Cell growth, cell division, membrane activity, enzyme
–is absorbed
by the plant (mass flow) Calcium flows to roots as transpirational water
Calcium deficiency is:
– Usually related to water supply
to the plant
– evident in blossom end rot
How is calcium lost from soil?
– Ca can leach in sandy, acid soils
– Highly weathered soils can be Ca?depleted
About ___ of plant Mg is in chlorophyll molecules
What are the micronutrients?
Fe, Mn, Cu, Zn, Ni, Mo, B, Cl
For most micronutrients, only a very small percentage of the total soil content of that nutrient is ________.
pH is often the single most important factor controlling ____________________________________.
transition metal micronutrient availability
Deficiencies can occur in basic soils because:
Solubility decreases as pH increases
__, __, ___ toxicities can occur in acid soils
Mn, Cu, or Zn
______ metals tend to be more soluble than _______ forms
___ and ___ are more available in wet soils
Fe and Mn
____ may become toxic in waterlogged soils
Chelates are:
soluble organic compounds that bind to metal ions
• increase the solubility of metals
• increase availability of metals to plants
Naturally produced chelates are:
– Produced by plant roots
– Present in humic substances
– Increase transition metal availability
EDTA, DTPA, EDDHA are examples of what?
Manufactured chelates
EDTA, DTPA, EDDHA are examples of what?
Manufactured chelates
Where is Boron toxicity commonly found?
Where irrigation water has high levels of Boron.
How does Boron deficiency happen?
Boron is easily leached from sandy or highlyweathered