1. Nutrient Cycling Mike Hubbs USDA-NRCS
National Nutrient Management Specialist
Washington DC
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2. NRCS Conservation Bootcamp
Nutrient Cycling N P C
Nutrient cycling is a function of soil K
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3. NRCS Conservation Bootcamp
Why are we interested in nutrient management? “Algal blooms” can occur as result of poor soil management that results in runoff. This eutrophication (enriching) is caused by N and P going into our surface waters.
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4. NRCS Conservation Bootcamp
Essential Plant Nutrients
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 by substituting another element
3) the element is needed by a wide variety of species from many different plant families
Plant require certain nutrients that are essential to their life cycles.
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5. 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
Cover slide
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6. Essential Plant Nutrients
C. HOPKIN’S CaFe, Mighty fine CuZine, Motley Manager, Burley Clerk
The Café will help memorize the essential nutrients. The 16 essential plant nutrients and forms taken up by plants are C=Carbon (CO2), H=hydrogen H2O), O=oxygen (H2O), P=phosphorus (H2PO4-, H2PO4-2-), K=Potassium (K+), N=nitrogen (NH4+, NO3-, S=sulfur (SO4-2), Ca=calcium (Ca+2), Mg=magnesium (Mg+2), Cu=copper (Cu+2,Cu+), , Zn=zinc (Zn+2), , Mo=molybdenum (MoO4-2, Mn=manganese( Mn+2), B=boron (BO3-3, B4O7-2), and Cl=chlorine (Cl-).
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7. NRCS Conservation Bootcamp
Essential Elements
Primary – N, P, & K
Secondary – Ca, Mg, & S
Minor – Zn, B, Mo, Cu, Fe, Mn, & Cl
Besides C, H, and O being taken up by CO2 and H2O, the rest of the nutrients are categorized into primary, secondary, and minor. The minor nutrients are essential, just in much smaller quantities.
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8. NRCS Conservation Bootcamp
Primary Nutrients
Form Taken Major Concentration
Element up by plants Source in plants
Nitrogen (N) NO3-, NH4+ Org. matter, – 6%
atmosphere
Phosphorus (P) H2PO4-, HPO42- Minerals, – 1.0%
org. matter
Potassium (K) K+ Soil minerals – 6.0%
Cover slide
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9. NRCS Conservation Bootcamp
Carbon
1) 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.
Cover that C is part of structural component of plants. Carbon is assimilated in plants by photosynthesis. Sugars are end products and energy is carbon cycled as CO2 by respiration.
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10. NRCS Conservation Bootcamp
Carbon (cont.)
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
Soil Organic Matter (SOM) is 58% carbon and can be 10 tons in an acre furrow slice, assuming 2% SOM.
Carbon is approximately 45% of plant dry weight or 25 ton wet basis corn crop at vegetative maturity, 2.8 ton of biomass and 0.7 ton root mass (3.5 ton/acre total.
CO2 is approximately 370 ppm in the atmosphere; if air weighs ~3,400 lbs per acre foot (density of 0.78) then the weight of CO2 in one acre foot of air is 1.25 lbs. Carbon is 0.27 of CO2 so one acre foot of air contains one third of a pound.
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11. NRCS Conservation Bootcamp
Loss of soil carbon (CO2) contributes to global warming or climate change. Other global warming gases related to carbon is CH4 (methane). Nitrous Oxide (N2O) is another global warming gas (denitrification).
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12. NRCS Conservation Bootcamp
Soil Carbon Cycle
ATMOSPHERE
CO2 O2
Photosynthesis O2
CO2
Decomposition
and exudation
Root
respiration
Microbial
respiration
Plant
uptake
Soil organic matter
including humus &
microbial biomass O2
The carbon cycle:
Carbon from the atmosphere is assimilated into the plant by photosynthesis. The plant is consumed or dies. The plant residues are decomposed by microorganisms and nutrients are mineralized. In the decomposition process, C is released back to the atmosphere. The process continues.
CO2
Rapid release
SOIL
Slow mineralization
Modified from Rowell (1994)
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13. 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
Plants contain 5-25% protein, which in turn contain 16-18% N.
(b) N in chlorophyll, nucleic acids, enzymes, and many other cells.
© N moves (translocates) from lower leaves to upper leaves; thus deficiency shows in lower leaves.
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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) lb N/ac per yr is deposited by precipitation
Almost all (95%) is in stable organic matter (humus) and unavailable for plant uptake
N.C.R. Res. Pub. No. 282 (1981) suggests that N deposited by precipitation amounts b. N/Ac or ~5-10% of fertilizer N used for corn production.
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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
Unavailable to plants, 90-95% of N is in organic form.
Organic N is mineralized into NH4+, then nitrified to NO3, is highly soluble ion readily available for plant uptake but also subject to leaching.
(© N in urea and NH4 in manure/biosolids can be lost as NH3 gas to the atmosphere by volatilization.
(d) No3 can be denitrified to N2 and N2O gases which can be lost to the atmosphere.
(e) Atmospheric N2 can be fixed into nodules by legumes (rhizobia) that will be mineralized to provide plant-available N (PAN).
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16. NRCS Conservation Bootcamp
Deficiencies of N in corn
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17. The Nitrogen Cycle Explain cycle NRCS Conservation Bootcamp
Atmospheric N2
Volatilization
loss of NH3
Removed from soil/plant system by harvesting
Industrial
fixation
Symbiotic fixation
(legumes)
Surface application of urea, manure, or biosolids
Nitrogen
fertilizer
Deposition of NO3- by precipitation
Gaseous loss of N2,N2O
Manure,
biosolids
Crop residue
Soil organic matter
(Organic N)
Plant uptake
1. Ammonification
4. Denitrification
Explain cycle
3. Immobilization
Ammonium N
(NH4+)
2. Nitrification
Nitrate N
(NO3-)
Removed from soil/plant system by leaching
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18. Phosphorus and Potassium
Mike Gangwer
USDA-NRCS Michigan
Nutrient Management Specialist
East Lansing, MI
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19. NRCS Conservation Bootcamp
Application of solid and liquid manure on crop fields during the non-growing season
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20. 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
1. Plants need a continuous supply for all cell division, including flowering, fruiting and seed formation.
2. Energy is necessary to build plant tissue and to absorb plant nutrients and water.
3. P is especially important during the reduction of CO2 in the Calvin Cycle, or reductive pentose phosphate cycle.
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21. NRCS Conservation Bootcamp
Phosphorus (cont’d)
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 mg/L (ppm) [ ppm for agronomic crops]
d) most crops contain % P (1,000 to 5,000 ppm Dry Weight)
a. ~50-70% is in “fixed” inorganic forms that are unavailable to plants.
b. In recently fertilized soils, can be 6-8 ppm P; 0.2 ppm P is used as the desirable concentration in the soil solution for plant growth.
d. Compared to levels of % for N and K, the other two primary nutrients
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22. NRCS Conservation Bootcamp
Phosphorus (cont’d)
Chemical forms of P in soils
a) H2PO4- > HPO42- pH below 7.2
b) HPO42- > H2PO4- pH above 7.2 (calcareous soils)
These are the forms of P absorbed by plants
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23. NRCS Conservation Bootcamp
Phosphorus (cont’d)
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
Ca, Fe, and Al phosphates become the primary inorganic form of P in soils.
d. In alkaline soils, P may precipitate on Ca carbonate surfaces.
e. In acidic soils P can adsorb on Fe and Al oxide surfaces.
f. Soluble P may react with noncrystalline forms of Fe and Al oxides to sorb and fix P into insoluble forms
Note that P has a lot going against it from the perspective of plant absorption; i.e. it is readily fixed by soil oxides in all pH ranges but especially at the ends of the agronomic range.
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24. NRCS Conservation Bootcamp
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”
Note the conversions of ppm to pounds per acre based upon an acre furrow slice
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25. NRCS Conservation Bootcamp

26. NRCS Conservation Bootcamp
Phosphorus deficiency in corn
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27. Municipal & Industrial By-Products Agricultural Residuals
Erosion, Runoff
Sediment & Soluble P
Plant Residues
Fertilizer
Plant Uptake
Sorbed P
Clays
Al, Fe Oxides
Sorption
Soil Solution P
HPO42- & H2PO4-
Desorption
Dissolution
Immobilization
Secondary P Minerals
Ca, Fe, Al phosphates
Precipitation
Mineralization
Explain forms and fates.
Organic P
Soil Biomass (living)
Soil Organic Matter
Soluble Organic P
Dissolution
Leaching
Primary P Minerals
Apatites
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(Redrawn from Pierzynski et al., 1994)

28. NRCS Conservation Bootcamp
Potassium
Potassium can be a herd health problem, especially in dairy cows, if the ration contains greater than about 3% K. Note that K can be luxuriously consumed on crop fields of grass after multiple applications of liquid manure are made. In most crop fields Mg occupies a greater exchange capacity than K on the CEC exchange suite.
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29. 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
a. Potassium is needed in large amount for maintenance of osmotic potential in cells, particularly in guard cells that open/close stomatal (leaf pores).
b. Due to its osmotic regulation.
d. With adequate K, cell walls are thicker and provide more tissue stability which improves resistance to lodging, pests and disease.
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30. 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 ppm) are available for plant absorption
a. Nearly all of this is a structural component of soil minerals, such as mica and feldspar.
b. This form of K is slowly available as these minerals slowly weather ( ppm).
c. Exchangeable K is usually present at ppm
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31. 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)
a. Primary and secondary K minerals. On clay mineral and organic matter negatively-charged surfaces
b. In equilibrium with exchangeable K+
c. Especially on manured fields
d. Note here the issue of dairy ration imbalances due to high K and lower Mg consumption
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32. 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”
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33. NRCS Conservation Bootcamp
Potassium deficiency in corn
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34. NRCS Conservation Bootcamp
Component
Input to soil
Loss from soil
The Potassium Cycle
Animal
manures
and biosolids
Crop
harvest
Plant
residues
Mineral
fertilizers
Runoff and
erosion
Exchangeable
potassium
Plant
uptake
Explain form and fates.
Soil solution
potassium (K+)
Fixed
potassium
Mineral
potassium
Leaching
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Potash & Phosphate Institute

35. 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.
Summary slide
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36. NRCS Conservation Bootcamp
Thank you
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