phosphorus and potassium
TRANSCRIPT
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Phosphorus
Macronutrient – essential element of ATP, RNA and DNA – essential element of cell membranes – yet still only 0.2% to 0.4% of leaves and
approximately 2% of OM dry weight– 1% to 4% of leaves and
approximately 2% of OM dry weight
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P Sources and SinksParent Material
– primarily apatite minerals, but other PM has…
range from 0.01% (100 µg/g) - 0.2% (2000 µg/g)
– native soil concentrations in 200 to 2000 µg/g (avg 1000)
Fertilizer and Manure– 10 to 15% of fertilizer
is taken up by plants
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P Sources and SinksSoil
– amount of P available for biological activity is small (@ 0.01%)
0.96 – 1.60 x 1012 kg
– bulk in 3 pools
Organic P, Ca-bound inorganic P and Fe/Al-bound inorganic P
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Fluxes
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Once again the question should be what controls these fluxes and reactions…
Organic P, Ca-bound inorganic P and Fe/Al-bound inorganic P
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P in soil solution range from 0.001 to 1 mg/L
Biological uptake is primarily in inorganic forms, though some organic P can be taken up…
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Issues of Soil Fertility
Issues of Environmental Quality
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Issues of Soil Fertility
– low native concentration levels– mostly in unavailable form (insoluble)– soluble forms can be quickly turned insoluble
Reminder: nutrients get to plants roots in the soil solution via concentration gradients
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Issues of Environmental Quality
– due to ↓ P supply in humid and subhumid regionsincreased intensity of slap and burn agricultureadditionally P deficiency inhibits microbial N-fixation
– P is limiting nutrient in freshwater environments addition can lead to eutrophication
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127 Soils from Delaware and the Netherlands (73 excessive)
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PotassiumMacronutrient
– cellular enzymatic activator – remains as K+ ion in organism – important regulator of cell osmotic potential– 1% to 4% of leaf content
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P Sources and SinksPrimary Minerals
– micas and feldspars = 90 to 98%
Secondary Minerals
– 2:1 phylosilicate clays = 1-10%
Soil Solution
– 0.1-0.2% in K+ form only
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Unlike previous nutrients, Potassium…
• is only present in soil solution in ionic form ~ K+
• usually in excess amounts ~ not limiting
• flux controlled by CEC & chemical weathering ~ no organisms
• causes no toxic consequence ~ not a toxic pollutant
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usually in excess amounts ~ not limiting
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flux controlled by CEC & chemical weathering ~ no organisms
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