Download Law of the barrel Limiting Nutrients N is responsible

Nutrients and Water Quality
Eutrophication - too many nutrients
• Adding nutrients to a
water system can upset
the balance
• Similar to adding BOD
• River or lake systems
are in a delicate balance
• Adding excess
nutrients causes the
wrong things to grow
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Law of the barrel
Sera 17
Limiting Nutrients
• Nitrogen and phosphorus are generally the two
most limiting nutrients in water systems
• Both macronutrients for plant growth
– This includes plants on the farm as well as plants in the
stream
• Adding excess causes excess growth including
algae
• What effects would this have on system?
N is responsible
• For lush green color
• Too much N can cause
excess growth
– Plants do not have sufficient
structural integrity to support
growth
– Lodging
• N deficiency = yellow leaves
– ‘Chlorosis’
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Nitrogen basics
• In atmosphere N2 gas (77% of
atmosphere)
• Where does soil N come from?
Fertilizers
• Organic
• Inorganic
– Manures
– Anhydrous ammonia
– Composts
– Ammonium nitrate
– Biosolids
– Urea
How does it go from
atmosphere to soil?
• Lightning N2
NO3
• Bacterial associations
One Example
N forms
• In soils 3 forms
– Organic N ( in plant and animal tissue)
N cycle
Organic N
N2 gas
– Mineral N
• NO3• NH4+
• Transformations in the form of N
are explained using the N cycle
Organic N
NO3 , NH4
Mineral N
Soil microbes
Or water microbes
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All transformations of N in soil
are microbially mediated
• Eating is the first step
• This is what happens when microbes eat
SOM, they need N to use the C
• Mineral N to organic N
– Immobilization
• Organic N to NH4+ or NO3 – Mineralization
Energy, respiration reactions
• NH4 + to NO3 - - nitrosimonas, nitrobacter
– Nitrification
• NO3- to gaseous N
– Denitrification
• Denitrification
– Occurs in anaerobic environments
– Wetlands, soil microsites
Phosphorous
Wetlands or water without O2
• When water is still
and O2 is depleted,
the microbes will
need an electron
acceptor
(remember eating)
• Primary function of
wetlands
• Very important plant nutrient
• Plants contain .2 % P
• Used in many functions including
ATP, seed germination,
photosynthesis, all growth and
metabolism
• P deficiency = purple leaves
P deficiency
Sources of P
• TSP
– Triple super phosphate
– Phosphate mines in ID and FLA
• Organic amendments
– Biosolids, manures
– Not all P is equally available
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SERA 17
Tendency to over fertilize with P
• Relatively immobile in soils
• Assure that you have sufficient amount
• Very high soil P
• So when soil erodes off of the field,
the river or stream gets all that P
laden sediment
USGS
Sediment - primary source of P
Irrigation
USGS
Irrigation
Irrigation
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Irrigation
Irrigation
Irrigation
Irrigation
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