ch.10 Flashcards
Major Elements
Carbon, Hydrogen, Oxygen
- Come from air and water and make mostly carbohydrates
Macro-nutrients
Nitrogen, Phosphorus, Potassium, Calcium, Magnesium, Sulfur
- Come from special bacteria, decaying organic matter, or weathering minerals in the soil
Micro-nutrients
Iron, Zinc, Manganese, Cobalt, Copper, Molybdenum, Sodium, Chlorine, sometimes Silicon, and others
Three Most Important Macro-nutrients
Nitrogen (N), Phosphorous (P), and Potassium (K)
- Amounts listed on front of fertilizer bags
Mechanisms of Nutrient Uptake: Nutrient Movement in Soil
Mass Flow
Diffusion
Interception
Mass Flow
Carried in gravitational water
Diffusion
From areas of high to low concentration in soil water
Interceptions
Roots grow into areas of nutrient concentration
Mechanism of Nutrient Uptake: Nutrient Absorption by Plant Roots
- Passive Intake
- Active Intake
Root cells contain membranes that are “semipermeable”; …
let certain ions in, keep others out
Passive Intake
Water and nitrate flow easily into root cells under normal conditions
Active Intake
Phosphorus and Potassium taken into root only by opening and closing special doors in the membrane, which takes energy from the plant
Nitrogen
- Most important agricultural nutrient
- Protein
- Locked up in organic matter or soil air as N2 gas
- “Fixation” : made into usable form
Microbial Nitrogen Fixation
Special enzyme called “Nitrogenase”
- Symbiotic
- Free Living
Symbiotic
By bacteria inhabiting plant roots
- Mostly Rhizobium, and Alder
- N2 to NH4
- Provides sugar and housing
- 330 lb/A of Nitrogen per year
Free Living
By bacteria living in soil rhizosphere
- Azotobacter main
-50 lb/A of Nitrogen per year
Mineralization of Nitrogen
- Soil organic matter contains 5% N
- Only reusable when released as NH4
- Natural decompostiton releases about 80 lb/A per year of rich soils. less in the West
Nitrification - NH4 to NO3
- Ammonia (NH4+) is tightly held on the soil exchange
- NO3 is much more immediately available to plants
- Several soil microbes (Nitrosomonas, Nitrobacter), can do this within weeks on warm, wet soils, even after heavy NH4 applications
Nitrogen Losses
- Leaching
- Denitrification
- Volatilization
Leaching
Nitrate is negatively charged = easily leaches
- Can easily pollute groundwater
- 20 lb/A loss per year
- Ammonia (NH4) fert. for slow leaching
Denitrification
NO3 can be changed back to N2 gas by certain soil bacteria
- about 15% loss of available Nitrogen per year
Volatilization
Ammonia can vaporize off as a gas
- Especially in basic soils
- 20% Nitrogen loss
Nitrogen Fertalizers
- Anhhydrous Ammonia (NH3)
- Urea (CO(NH2)2)
- Ammonium Nitrate (NH4NO3)
- Ammonium SUlfate (NH4SO4)
Nitrogen Others
- Organic Wastes
- Slow release formulations
Anhydrous Ammonia (NH3)
- Most common commercial formulation
- Relatively cheap
- App. w/ injection machines under pressure
- Rel. hazardous, very caustic, must use protective equipment
Urea (CO(NH2)2)
- Naturally urine, but also made synthetically
- Slow release and safe
- Mod. price
- Granular or liquid
Ammonium Nitrate (NH4NO3)
- Highest analysis for Nitrogen at about 45% by weight
- very rapid avail. of Nitrate and Ammonium
- Explosives, not sold anymore
Ammonium Sulfate (NH4SO4)
- 21% Nitrogen by weight
- Also supplies needed Sulfur
- Most used Granular, non-commerical
- Strong acid former
Organic Wastes
Composts, Manures, Sludge
- Only 1-8% Nitrogen
- Very expensive for large areas
- Not economical, mostly organic amendments
Slow release formulations
Special mixed formulations that release over extended periods
- Polyform UF, Ureaform, Osmocote, Sulfocote, etc.
- Very expensive
- Used exclusively for ornamentals
Phosphorus
- Second most important
- All energy reactions (ATP)
- Most imp. for legumes (pea fam)
- Plenty is western soils
- Very slowly released from soils to plants
Minerals 1
“Apatite” or rock phosphate (CaS(PO4)3)F
Minerals 2
- Most common soil minerals cont. phosphorous
- Slowly hydrolyzes to phosphoric acid via several insoluble intermediates
- Fast @ pH 6.5
- Mycorrhizal fungi
break down
materials much
faster - Moves in soil sol.
rapidly once
hydrolized
Organic Matter
Up to 80% of soil P from OM
- Supplies half needed P in crops in MidWest
- Broken off from soil OM by phosphatase enzyme from plant roots and soil microbes
- Phosphates also major enzyme found in Mycorrhizal fungi
Phosphorus Fertilizers
- Pure Rock Phosphate
- Phosphoric Acid
- Superphosphate
- Concentrated or Triple Superphosphate
Pure Rock Phosphate
Ground up Apatite
- About 32% P, almost none quickly to plant
- Cheap, further refining
Phosphoric Acid
Byproduct of refining process, often sold as fertalizer
- about 40% P, much immediately available to plant
- many times liquid form., need special applic.
Superphosphate
Hydrated Ca phosphate
- Very common fert.
- About 20% usable P, very safe
Concentrated or Triple Superphosphate
Less hydrated and more concentrated calcium phosphate
- Very common, home use
- Abt 45% usable P
- Very safe
- Fairly expensive
Potassium
- Total soil is huge, esp in West, but most tied up in minerals, not soluble
- Very slow weathering from mice and feldspar
- Abt 150% ib/A avail. in most soils, high production crops need more
- Needed for plant cell membrane function including water Uptake and disease resistance
- Very non soluble in acid soils, needed east more than out west
Potassium Losses
- Luxury consumption
- Soil microbes
- Clay particles
- Leaching
Luxury Consumption
Many plants store Potassium in Amounts higher than needed
- Store much per acre, released after death
Soil Microbes
Can also concentrate Potassium up to thousands ibs/A
- Released upon microbe death
Clay Particles
Held tightly to ion exchange, many times too tightly to be released to plant roots
- Overcome by shear amounts in most soils
Leaching
Only in sandy soils
Potassium Gains
- Mineral weathering
- OM breakdown
- Released from exchange
Minerals Weathering
Especially of Mica and Feldspar
- Main release method in low OM western soils
OM Breakdown
Especially important in eastern soils where it is the main supply mechanism
Released from Exchange
Depends on Clay type
- 2:1 clays exchange better than 1:1
- Very slow
Potassium Fertalizers
-Potash (KCI)
- Potassium Sulfate (K2SO4)
Potash - Potassium Chloride (KCI)
1 Potassium fertalizer in US
- Mined in western US, Utah and Mexico
- Salt brine in salt lakes, Searl’s Lake by Trona
- Add. of CI ion = prob
- 50% usable potassium
Potassium Sulfate (K2SO4)
- Much like potash, no CI ion and good source of sulfur
- Much more expensive than potash
