NRCS Conservation Bootcamp Nutrient Cycling Mike Hubbs USDA-NRCS National Nutrient Management...

NRCS Conservation Bootcamp

Nutrient Cycling

Mike HubbsUSDA-NRCS

National Nutrient Management Specialist

Washington DC


Nutrient CyclingNutrient Cycling

K

C

N

P


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



• 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



C. HOPKIN’S CaFe, Mighty fine CuZine, Motley Manager, Burley Clerk


Essential Elements

• Primary – N, P, & K

• Secondary – Ca, Mg, & S

• Minor – Zn, B, Mo, Cu, Fe, Mn, & Cl


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%


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.


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


Soil organic matterincluding humus &microbial 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


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


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


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


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


Phosphorus and Potassium

Mike GangwerUSDA-NRCS Michigan

Nutrient Management SpecialistEast Lansing, MI


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


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)


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


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


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”


(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


Potassium


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


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


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)


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”


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


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.


Thank you

NRCS Conservation Bootcamp Nutrient Cycling Mike Hubbs USDA-NRCS National Nutrient Management...

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