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NRCS Conservation Bootcamp
Nutrient Cycling
Mike HubbsUSDA-NRCS
National Nutrient Management Specialist
Washington DC
NRCS Conservation Bootcamp
A plant nutrient is considered essential if:
1) a deficiency of the element makes it impossible for the plant to complete its
life cycle (plant will die)
2) the deficiency cannot be corrected bysubstituting another element
3) the element is needed by a wide variety ofspecies from many different plant
families
Essential Plant Nutrients
NRCS Conservation Bootcamp
Essential Plant Nutrients
• Green plants need 16 essential nutrients
• Plants get C, H, and O from air & water
• The remaining 13 elements come from soil– N, P, K, Ca, Mg, S, B, Cl, Cu, Fe, Mn, Mo, and Zn
NRCS Conservation Bootcamp
Essential Plant Nutrients
C. HOPKIN’S CaFe, Mighty fine CuZine, Motley Manager, Burley Clerk
NRCS Conservation Bootcamp
Essential Elements
• Primary – N, P, & K
• Secondary – Ca, Mg, & S
• Minor – Zn, B, Mo, Cu, Fe, Mn, & Cl
NRCS Conservation Bootcamp
Primary Nutrients
Form Taken Major ConcentrationElement up by plants Source in plants
Nitrogen (N) NO3-, NH4
+ Org. matter, 1 – 6%atmosphere
Phosphorus (P) H2PO4-, HPO4
2- Minerals, 0.05 – 1.0%
org. matter
Potassium (K) K+ Soil minerals 0.3 – 6.0%
NRCS Conservation Bootcamp
Carbon1) Function in plants
a) Carbon is part of the structural component of plant as well as the seed component.
b) CO2 is assimilated in the plant leaf via photosynthesis
c) Carbohydrates are end products of photosynthesis and are used for energy
and respiration.
NRCS Conservation Bootcamp
Carbon (cont.)2) Content in soil, plants, and air
a) Carbon is approximately 58% of SOM
b) Carbon is approximately 40% of plant dry weight
c) CO2 is approximately 370 ppm (0.03 %) in the atmosphere
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Soil organic matterincluding humus µbial biomass
SOIL
ATMOSPHERE
Rootrespiration
Slow mineralization
Microbialrespiration
Rapid release
Plantuptake
Photosynthesis
O2
CO2
CO2
CO2
O2
O2
Modified from Rowell (1994)
Soil Carbon Cycle
Decompositionand exudation
NRCS Conservation Bootcamp
Nitrogen
1) Function in plants
a) N is a major constituent of protein
b) N in chlorophyll, nucleic acids, enzymes, and many other cellular compounds
c) N is mobile within the plant and when a deficiency occurs in lower leaves
NRCS Conservation Bootcamp
Nitrogen (cont’d)
2) Content of N in crops, atmospheric emissions and depositions of N, & available amounts in soils
a) soil often contains 2,000-6,000 lb N/ac in the plow layer (acre furrow slice)
b) 4.5-13.5 lb N/ac per yr is deposited by precipitation
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Nitrogen (cont’d)3) Chemical form of N in soils
a) Approximately 95% N – organic form
b) NH4+ and NO3
- is mineralized and is available
d) NO3- can be denitrified to N2 and N2O gases
e) atmospheric N2 can be fixed into nodules by legumes
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Deposition of NO3
- by precipitation
Gaseous loss of N2,N2O
The Nitrogen Cycle
1. Ammonification
Removed from soil/plant system by harvesting
Crop residue
Manure,
biosolids
Atmospheric
N2
Soil organic matter
(Organic N)
Ammonium N
(NH4+)
Nitrate N
(NO3-)
Symbiotic fixation
(legumes)
Volatilization
loss of NH3
Nitrogen
fertilizer
Surface application of urea, manure,
or biosolids
Plant uptake
Removed from soil/plant system by leaching
2. Nitrification
3. Immobilization
Industrial
fixation
4. Denitrification
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Phosphorus and Potassium
Mike GangwerUSDA-NRCS Michigan
Nutrient Management SpecialistEast Lansing, MI
NRCS Conservation Bootcamp
Phosphorus
1) Function in plants
a) P is a major constituent of the nucleus of plants,
b) P is also found in compounds ADP and ATP that store and transfer energy within the plant,
c) P is involved in nearly all metabolic processes
NRCS Conservation Bootcamp
Phosphorus (cont’d)2) Content of P in crops and available amounts in
soils
a) soils generally contain 50-1,500 ppm (100-3,000 lb/ac)
b) soluble forms of fertilizer P are quickly converted to less available forms when added to soils.
c) concentration of P in soil solution is usually <0.01 to 1 mg/L (ppm) [0.1-0.3 ppm for agronomic
crops]
d) most crops contain 0.1-0.5% P (1,000 to 5,000 ppm Dry Weight)
NRCS Conservation Bootcamp
Phosphorus (cont’d)
3) Chemical forms of P in soils
a) H2PO4- > HPO4
2- pH below 7.2
b) HPO42- > H2PO4- pH above 7.2 (calcareous soils)
These are the forms of P absorbed by plants
NRCS Conservation Bootcamp
Phosphorus (cont’d)3) Chemical forms of P in soils
c) weathering causes secondary P fixation of Ca, Fe, and Al phosphates
d) alkaline soils, Ca phosphates form
e) acidic soils, Fe and Al phosphates form
f) soil Fe and Al oxides, and some clays fix soluble P
These forms of P are unavailable for plant absorption
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Soil P and Nutrient P2O5 Relationships● ppm P x 2 = lb P/acre (or pp2m)
2,000,000 lb/afs (afs = acre furrow slice)
● lb P x 2.3 = lb P2O5
● for nutrient additions from fertilizers & organic residuals (example: manure), use lb of P2O5
● for P removal by plants, use lb of P2O5
● for soil test P (STP) levels, use “lb P” or “ppm P”
NRCS Conservation Bootcamp
(Redrawn from Pierzynski et al., 1994)
Soil Solution PHPO4
2- & H2PO4-
Sorbed PClays
Al, Fe Oxides
Primary P MineralsApatites
Secondary P MineralsCa, Fe, Al phosphates
Organic PSoil Biomass (living)Soil Organic MatterSoluble Organic P
Immobilization
Mineralization
Sorption
Desorption
PrecipitationDissolution
Dissolutio
n
Leaching
Plant Uptake
Erosion, RunoffSediment & Soluble P
Fertilizer
Plant Residues
Agricultural Residuals
Municipal & Industrial By-Products
NRCS Conservation Bootcamp
Potassium (cont’d) 1) Function in plants
a) unlike N and P, K+ does not become part of organic compounds in plants
b) K+ is involved in water uptake from soil, water retention in plant tissue, and transport of
water within the plant
c) K+ balances the negative charges of organic and inorganic anions
d) K+ helps maintain turgor, or cell pressure
NRCS Conservation Bootcamp
Potassium (cont’d)2) Content of K+ in crops and available amounts in
soils
a) soils generally contain over 20,000 ppm (40,000 lb/ac) of K+
b) nonexchangeable K+ within clay mineral layers is fixed
c) exchangeable K+ on clay mineral surfaces and K+ dissolved in the soil solution (usually 1-10 ppm) are available for plant
absorption
NRCS Conservation Bootcamp
Potassium (cont’d)
3) Chemical forms of K in soils
a) as soils weather, K minerals release K+ ions for adsorption onto cation exchange sites
(CEC)
b) occurs in soil solution as K+ ions and are available to plants for absorption
c) quantities in soils will vary greatly
d) excess exchangeable K+ levels can induce a Mg2+ deficiency in plants (dairy feed ration)
NRCS Conservation Bootcamp
Soil P and Nutrient K2O Relationships● ppm K x 2 = lb K/acre (or pp2m)
2,000,000 lb/afs (afs = acre furrow slice)
● lb K x 1.2 = lb K2O
● for nutrient additions from fertilizers & organic residuals (example: manure), use lb of K2O
● for K removal by plants, use lb of K2O
● for soil test K (STK) levels, use “lb K” or “ppm K”
NRCS Conservation Bootcamp
The Potassium CycleAnimal
manuresand biosolids
Mineralfertilizers
Crop harvest
Runoff anderosion
Leaching
Soil solution potassium (K+)
Plant residues
Plantuptake
Mineralpotassium
Fixedpotassium
Exchangeable potassium
Input to soilComponent Loss from soil
Potash & Phosphate Institute
NRCS Conservation Bootcamp
Summary
• Know the importance of nutrient cycling through the farm system.
• Know the chemical forms of CNPK in terms of organic and inorganic specie.
• Know that for developing a nutrient management plan as part of a Conservation Plan, the planner will use the criteria in state eFOTG 590 Standard Nutrient Management.
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