FORMS OF PHOSPHORUS IN THE SOIL

1
FORMS OF PHOSPHORUS IN THE SOIL

• Inorganic (50-70 of soil P)
• Bound (Fixed)
• Bound to Al, Fe and Ca cations on soil clay
  particles
• Dependent on soil pH
• Binding cations Optimum pH
• Al, Fe
  4 - 5
• Ca
  7 8
• Most P in soil
• Binding occurs rapidly when any P is applied
• Most fixed in the upper 2 5 inches of soil
• Less P fixed in sandy or peaty soils with high
  infiltration rates
• Bound P is unavailable to plants
• Primarily pollutes water sources with soil
  erosion
• Available P (Labile)
• P that is not fixed or has been released from
  bound P
• Forms
• Orthophosphate (HPO4, H2PO4)
• Usually present in very low amounts
• Dependent on

2

• Conversion of bound P to soil available P is a
  slow process
• Most soil tests measure available P, not total P
• Available P is water soluble
• May move with subsurface water flow to surface or
  subsurface water resources
• 60 90 of the P in animal manure is in an
  inorganic available form
• Organic P
• Bound
• P that is immobilized by microbial conversion of
  organic P into more resistant and stable forms of
  organic P
• Increases with increasing CarbonPhosphorus
  ratios
• Greatest at CP ratios gt 3001
• Transported with soil erosion to water sources
• Available
• P in undecomposed plant residues and microbes
• Must be converted to inorganic P by microbial
  mineralization before being used by plants
• Available organic P is often water soluble
• Sources of dissolved organic P
• Decaying plant material
• Manure
• Transported with run-off or subsurface water

3
FORMS OF PHOSPHORUS IN SOIL
4
P FERTILITY

• Discussed as P2O5
• Calculated by multiplying P by 2.29

5
P TRANSPORT IN THE ENVIRONMENT

• Forms
• Sediment P
• Includes
• Fixed inorganic
• Bound organic
• Transported with sediment associated with soil
  erosion
• Primary form lost from cultivated land or from
  stream bank erosion in pastures
• Slowly supplies P for algae growth in water
  sources
• Dissolved P
• Includes
• Available inorganic P
• Available organic P
• Amount increases with increasing P content of
  soil
• Transport by
• Surface run-off
• Subsurface flow and tile
• Primary form of P in run-off from land covered
  with vegetation
• Immediately available for algae growth

6
P TRANSPORT IN THE ENVIRONMENT
7
EFFECTS OF P ON ENVIRONMENTAL QUALITY

• Eutrophication of surface water sources
• Primary cause of eutrophication of fresh water
  sources
• Algae in fresh water sources can use atmospheric
  N2 as N sources
• P limits algae growth
• Recently identified as the major cause of the
  hypoxic (dead) zone in the Gulf of Mexico
• Effects
• Excessive growth of undesirable algae and plants
• Results in O2 shortage as algae and plants die
  and decay
• May result in blooms of cyanobacteria and harmful
  algae like Pfiesteria piscida.
• Results
• Summer fish kills
• Taste, odor and treatment problems in water
• Increased water turbidity
• Decreased recreational use
• P levels
• Eutrophication
  .02 mg/l
• Plant growth .2
  - .3 mg/l
• Water quality standards
• Streams entering lakes
  .05 mg/l (50 ppb)

8
P CONCENTRATION IN IOWA LAKES (2001)
9
CHANGE IN THE CONCENTRATION OF P IN MAN-MADE
LAKES IN IOWA
10
LIVESTOCK AND LOADING OF P IN THE ENVIRONMENT

• Concentration of livestock production
• 31 of farms in US have inadequate land to apply
  P from the manure produced
• Manure from these farms represents 70 of the
  excess manure P produced
• 5 of the counties have inadequate land to apply
  P from the manure produced
• Manure from these counties represents 23 of the
  excess manure P

11

• The low NP ratio of manure relative to crop
  needs
• Crop NP2O5 needed Livestock NP2O5
  excreted NP2O5 available
• Corn grain 2.5 Swine (G-F)
  1.15 .88 (Slurry)
• Soybeans 4.26 Beef feedlot
  1.41 .75 (Scraped)
• Alfalfa 4.5 Lactating dairy
  cow 2.45 .88 (Slurry)
• Bromegrass 3.88 Layer
  1.15 .88 (Slurry)
• Corn silage 1.95 Turkey
  1.17 .75 (Litter)
• 
  
  w/ incorporation
• Results in excess P accumulation in soil if N is
  applied at the agronomic rate
• Problem is enhanced by N volatilization

12

• Low P retention
• 
  retained
• Growing cattle
  21
• Growing swine
  27
• Poultry
  21
• Grazing cattle
• Little P removed by grazing cattle
• Most P is recycled to the soil
• Pastures generally are not good places to
  repeatedly fertilize with swine and poultry
  manure unless periodically baled
• Stream bank erosion
• Poorly managed grazing may remove vegetation from
  stream banks allowing soil erosion
• With increasing soil erosion, P pollution of
  streams will occur

13
FUNCTIONS OF P IN LIVESTOCK

• Bone structure
• 80 of the bodys P
• Bound to calcium as hydroxyapatite crystals
• Ca10 x(PO4)6(OH)2(H3O)2x
• CaP ratio 21
• Serves as a reserve source for Ca and P for other
  functions
• Energy metabolism
• Adenosine triphosphate (ATP)
• Creatinine phosphate
• Genetic structure
• Nucleic acids
• Cell membranes and organelles
• Phospholipids
• Phosphoproteins
• Acid-base balance
• Microbial growth and digestion in the rumen of
  ruminant animals

14
P DEFICIENCY SYMPTOMS

• Bone abnormalities
• Weak, bent, easily broken
• In young animals, rickets
• In adult animals, osteomalacia
• Loss of appetite or depraved appetite
• Animals eat unusual materials like pebbles,
  metals etc.
• Behavior does not represent a sense for P in
  feeds
• Unthrifty appearance and loss of growth
• Reduced milk production
• In swine, paralysis of the hind limbs
• In cattle, reduced fertility
• Questionable concern
• Only occurs when cattle are fed very low P levels
  (lt .2P) for long periods of time
• May be the result of impaired feed digestion by
  not meeting the microbial needs

15
P IN FEEDS

• P concentration in feeds
• P concentration in most feeds except mature
  forages is moderate to high.
• Livestock species Total P reqt. Feed
  class Feed P, DM
• Dairy cow
• Lactating .40
  Energy conc Corn .30
• Dry .25
  Oats
  .40
• Beef
  Cottonseed
  .60
• Finishing steer .24
  Protein conc Soybean meal .71
• Lactating cow .22
  Meat and bone 4.73
• Dry cow .12
  Grain Wheat mids
  1.02
• Swine
  processing Distillers grains
  .83
• Growing-finishing .4 - .6
  byproducts Corn gluten feed1.00
• Sow .6
  Forages Corn silage
  .28
• Poultry
  Alfalfa hay
  .31
• Layers .4
  Grass hay
  .30
• Broilers .4
  Grass pasture
  .40
• Turkeys .6
  Corn stalks
  .09

16

• Availability of P in feeds
• 60 75 of P in grains, grain by-products, and
  oilseed meals is bound to form phytate
• Phytate-phosphorus is unavailable to monogastric
  animals
• Phytate-phosphorus is degraded by the enzyme,
  phytase, produced by the rumen bacteria in
  ruminant animals

17

• P availability
• 
  Swine and poultry Cattle
• 
  ( available)
• Corn and corn byproducts 15
  70
• Wheat
  50 70
• Soybean meal
  25 70
• Meat and bone meal
  67 -
• Forages
  - 64
• Dicalcium phosphate
  100 70
• Defluorinated phosphate
  95 70
• Must compensate for the low availability of
  phosphorus from plant sources in monogastrics by
  supplementing mineral sources
• Results in increase P excretion

18
P DIGESTION AND METABOLISM IN NONRUMINANTS

• Small intestine
• Phytate-P
• (60-75 of plant P)
• 
  Excess Ca or high pH
  Feces
• Inorganic P
• Passive
  Active
• 
  absorption transport
• 
  Circulating P
  1,25(OH)2vitamin D
• 
  
  kidney
• Bone
  
  (Low blood Ca or P)
• Soft tissue
  25 (OH) vitamin
  D
• 
  Excess (Circulating
  in blood)
• 
  
  Liver
• 
  Kidney Vitamin D
• 
  (Diet or
  sunlight)

19

• Factors affecting P absorption from the gut
• Phytate
• High phytate reduces P absorption
• CaP ratio
• CaP should be between 11 to 1.251
• Intestinal pH
• High intestinal pH reduces P absorption
• Vitamin D
• Vitamin D deficiency reduces P absorption

20
STRATEGIES TO LIMIT P LOADING OF THE ENVIRONMENT
BY NONRUMINANT ANIMALS

• Increase availability of dietary P
• Degrade phytate-P
• Feed microbial phytase
• Enzyme produced by fungus, Aspergillus sp.
• Treatment
• 200 to 1000 units/kg
• 500 units 90 gm/ton
• Effects
• Decrease P excretion by 30 to 50
• Increases availability of some other minerals and
  amino acids
• Most activity occurs in stomach or gizzard
• Optimal activity occurs at pH lt4.0
• Effectiveness decreased if
• Excess Ca is fed
• Vitamin D is deficient
• Phytase is applied before pelleting feed
• Temperatures greater than 140 F destroys
  enzyme
• Effectiveness improved if
• Fed as an enzyme cocktail with phosphatase,
  protease, citric acid, and pectinase

21

• To reduce P excretion when using phytase, rations
  must be balanced to meet the available P
  requirement
• Phytase can reduce the amount of inorganic P
  supplemented in swine and poultry diets by .1
  unit or 25
• Example (Swine)
  1000 head Farrow-finish
• 
  P in phases Manure P (lb P2O5/yr)
• Normal diet .60,
  .55, .50, .45 13,000
• Phytase-treated .50, .45,
  .40, .35 8,900
• Economics of using phytase
• Cost of phytase cost of dicalcium phosphate
  saved
• Genetically modify crops to contain phytase
• Successful in corn and soybeans
• Limitations
• Susceptible to destruction from heating during
  processing
• Difficulty in separating genetically modified
  crops from other varieties

22

• Genetically modify swine to have phytase in
  saliva
• Gene from Escherichia coli has been inserted into
  swine
• Phytase secreted in saliva of GM pigs
• Stable at pH 2.5
• Resistant to pepsin
• Decreases P excretion by 60
• Limitations
• Variable response
• Regulator and consumer concerns with GMO foods
• Possible allergenicity to E. Coli proteins
  that are resistant to digestion in the stomach
• Genetically modify crops to decrease phytate
  content
• Reduces phytate content of corn and soybean meal
• 
  Phytate-P, of total P
• 
  Normal Low phytate
• Corn
  75 35
• Soybeans
  70 24
• Increases P bioavailability
• 
  P bioavailability,
• 
  Normal Low phytate

23

• Limitations of low phytate crops
• Low germination rates
• 4 23 reduction in seed weight
• Difficulties in separating grain hybrids
• Addition of vitamin D metabolites
• 1,25(OH)2 vitamin D increases P transport across
  intestinal wall
• Has additive effects with phytase
• Feeding 1,25 (OH)2 vitamin D and phytase can
  replace .2 units or 50 of the inorganic P added
  to chick diets
• Limitation
• Excess vitamin D may be toxic
• Addition of probiotics
• Probiotics are microbial cultures dosed or fed to
  establish a population of favorable bacteria
• Feeding Lactobaccillus-based cultures increase P
  retention by 22 in chickens

24

• Balance diets closer to the P requirements
• Limit safety margins
• Swine industry commonly feeds P at 120 155 of
  the NRC requirements
• Swine diet
  Manure P, lb/pig
• .5 P
  2.5
• .6 P
  3.5
• Current actual requirements for poultry are 40
  less than recommended by NRC
• Phase feeding
• P requirement (as a of diet) decreases as
  animals grow
• Increasing number of phases to 4 or 5 or more
  will reduce P excretion by 10
• Limitation
• Feeding and handling more diets
• Separate sex feeding
• P requirements for males gt P requirements for
  females
• Accurate real-time feed composition
• Book values are inaccurate
• Wet lab analysis of P and phytate-P is slow and
  expensive
• Near infrared reflectance spectroscopy (NIRS)
  technology may help

25

• Minimize feed variability
• Natural variability
• Processing
• Pelleting may reduce P bioavailability
• Proper weighing and mixing
• Minimize feed waste
• Each 1 increase in feed waste .04 lb/pig
  increase of P in manure
• Total potential for using available tools
  (phytase, low phytate corn, phase feeding,
  vitamin D)
• Decreases P excretion by 40 to 60 in poultry
• Decreases P excretion by 50 to 60 in swine

26
P DIGESTION AND METABOLISM IN RUMINANTS

• Rumen
  Small intestine
• Phytate-P
• Inorganic-P Undegraded
• Degraded
  Very little
  Feces
• 
  
  (95-98 of
• Inorganic P
  
  excreted P)
• 
  
  
• Microbes
  Passive Active
• 
  absorption transport
• 
  Circulating P
  1,25(OH)2vitamin D
• 
  
  kidney (Low Ca
• Recycled to digestive Bone
  
  or P)
• tract via saliva
  
  25(OH)vitamin D
• (Supplies P to rumen Soft
  tissue
• microbes if diet is deficient
  
  liver
• 80 of total P excreted)
  Excess

27
FACTORS AFFECTING P ABSORPTION IN RUMINANTS

• Amounts of P consumed
• High P intake reduces P absorption
• CaP ratio
• Optimum is 21
• Excess amounts of Al, Fe, Mg, Mn, K, and fat
• Reduce P absorption by producing indigestible
  complexes
• Intestinal pH
• Lower intestinal pH increases P absorption
• P source
• 
  P availability,
• Forages
  64
• Energy and protein concentrates 70
• Mineral supplements
  70
• Forage P concentration
• High soil P increases forage P concentration
• High forage P concentration reduces P absorption
• Forage maturity
• Forage P concentration decreases with maturity
• Forage fiber digestion decreases with maturity
  decreasing P absorption

28
STRATEGIES TO REDUCE PHOSPHORUS LOADING OF THE
ENVIRONMENT BY RUMINANTS

• Do not overfeed P
• Dairy
• 
  P in DM Manure P, lb/cow/lactation
• Industry average
  .52 64.9
• NRC requirement
  .32-.42 42.2
• Adequate
  .35 34.8
• Dry cow
  .25 -
• Reasons for excess feeding
• Belief that P supplementation will improve
  reproductive performance
• Studies show no improvement in reproduction above
  .25 P
• Aggressive marketing of P supplements
• Beef feedlot
• Steer (600-1200 lb)
  Diet P, of DM
• NRC requirement
  0.20 0.30
• Adequate in experiments
  0.14 0.16
• Reasons for excess feeding
• NRC requirement based on 1950 dairy cow data
• High grain diets contain 0.3 and require no
  supplement

29

• Beef cows
• Common P,
  Physiological P reqt,
• Season feed of DM
  state of DM
• Spring-summer Pasture 0.37-0.44
  Lactating 0.22
• Fall Corn stalks 0.09
  Early gestation 0.12
• Winter Grass-legume hay 0.26-0.34 Late
  gestation 0.16
• Implications
• Phosphorus only need to be supplemented when
  grazing or fed very mature grass forages or crop
  residues
• However, most producers supplement P year-round
• Reasons for excess P feeding
• Belief that continuous P supplementation is
  needed for reproductive performance
• Ease of supplementing minerals free choice to
  provide safety margin
• Results of feeding excess P
• Increases amount of P excreted
• Increases the solubility of the P excreted
• Amount of P lost in run-off increased 4 times if
  dairy cow diets contain .5P vs. .4P

30

• Difficulty in lowering P in ruminant diets
• High concentration of P in grains and grain
  by-products
• Grains contain adequate P (0.3) to meet
  requirements of feedlot cattle without supplement
• Grain by-products
• Contain high concentrations of P
• 
  P, DM
• Wheat mids
  1.02
• Distillers grains
  0.90
• Corn gluten feed
  1.00
• A large increase in ethanol plants will increase
  the amounts of distillers grains available
• 75 of distillers grains are fed to beef
  cattle
• A diet containing 40 distillers grains will
  contain 0.55 P
• If by-products are fed, more land will be needed
  to apply at an agronomic rate
• Strategic use of P reserves in cows
• Dairy cows may safely mobilize 500 to 1000 g P
  from bone in early lactation
• Could also be used for intervals in beef cows
• Ruminants effective at recycling P
• Mobilized P must be replaced at different times
  of the year

31

• Feeding ionophores
• Chemical feed additives that affect mineral
  transport across membrane
• Common ionophores
• Monensin (Rumensin)
• Lasalocid (Bovatec)
• Reduces P excretion
• Monitor feed status
• Analyse feeds
• Books values are inadequate
• Condition score cows
• Measure of cow fatness
• Scale (1 9)
• 1 very thin
• 5 desired
• 9 very fat
• If cows lt condition score 5, analyse diet for
  energy, protein and minerals
• P solubility in feces
• No soluble P means inadequate P in diet

32

• Feed high quality forages
• Immature, high quality forages contain more P
  that is more digestible than mature forages
• Avoid excess calcium in diet
• Use improved grazing management practices
• Properly managed rotational grazing should limit
  P loss in soil erosion from both upland and
  riparian areas
• Bale some pasture forage to remove P and to keep
  the remainder of the pasture immature
• Only fertilize pastures with P based on soil
  analyses
• Strategic supplementation to grazing cattle
• Only supplement if grazing mature forage on low P
  soil
• Limit use of free choice mineral
• In future, may be able to feed grains that are
  genetically modified for a lower P content.

33
POTENTIAL TO DECREASE P EXCRETION BY RUMINANTS

• Dairy
• 20 decrease in dietary P
• 25 30 decrease in manure P
• 50 decrease in P run-off from land
• Beef
• 33 decrease in dietary P
• 40 decrease in manure P (5.1 lb P/steer)

34
MANURE HANDLING AND STORAGE TO MINIMIZE P LOADING
OF THE ENVIRONMENT

• Goals
• Maintain NP ratio
• Use strategies to minimize N loss
• Minimize P loss
• Minimize precipitation run-off
• P loss from lots and storage facilities is low if
  run-off is minimized
• Strategies
• Catch run-off from lots and storage areas
• Divert clean water from lots and storage areas
• Minimize the solubility of P in manure
• Gravity settling and mechanical separators will
  remove 15 to 25 of the P in liquid manure
• P decreases in the liquid fraction of manure in
  lagoons and increases in the sludge
• 65 of the P in manure will be in the sludge
• Addition of aluminum sulfate, magnesium chloride,
  ferric chloride, and some Ca salts will
  precipitate P from liquid manure in the solids
  fraction
• Enhance manure transport from farm
• Compost

35
LAND APPLICATION STRATEGIES TO LIMIT P LOADING OF
THE ENVIRONMENT

• Goals
• Apply manure to meet crop P needs
• Apply manure to minimize risk of P transport to
  water sources
• Considerations
• Should manure be applied?
• Application rate?

36
METHODS TO DETERMINE WHETHER MANURE P SHOULD BE
APPLIED

• Soil tests
• Measures available P relative to plant response
• If soil test is high or very high
• Manure should not be applied or applied only at
  the agronomic rate depending on transport risk
  determined by a P index
• P index
• A measure of the risk of P transport to surface
  water sources
• Required for every field which manure applied on
  it from a CAFO in Iowa
• Integrates soil, landscape, and management
  factors that influence P transport to surface
  water sources
• Identifies causes of P delivery and provides
  options to decrease P transport

37

• Considerations for the Iowa P index
• Erosion component
• Gross erosion (Slope, soil type, cover)
• Sediment trapping (Conservation practices)
• Sediment delivery (Amounts of sediment and
  distance from stream)
• Buffers
• Soil P test erosion (Sediment-bound P loss)
• Run-off component
• Run-off (Soil drainage)
• Precipitation (Annual)
• Soil P test run-off (Soluble P loss in run-off)
• P application (Total P fertilization)
• Subsurface drainage component
• Precipitation (Annual
• Flow factor (Presence of subsurface strata)
• Soil P test infiltration (Soluble P infiltrating
  soil in drainage

38

• Ranks risk of application site from 0 to 15
• Interpretation
• Very low (0 1)
• Effects of P losses from a field will be small
• Low (1 2)
• Current soil conservation and P management
  practices do not pose threat
• Medium (2 6)
• P delivery potential is low, but improved soil
  conservation and P management practices should be
  considered
• High (6 - 15)
• Impacts of P on surface water is high. Improved
  soil conservation and P management practices to
  reduce P transport are required.
• Very high (gt 15)
• Impacts of P on surface water is extreme.
  Improved soil conservation and P management
  practices to reduce P transport are required.
• P management plan that may include
  discontinuation of P application must be
  implemented.

39
CALCULATION OF MANURE APPLICATION RATE BASED ON
THE AGRONOMIC RATE FOR P

• Manure P production or concentration
• Manure_________
  P2O5, lb/lb animal wt/yr
• Swine Growing-finishing
  0.13
• Sows litter
  0.12
• Sows (gestation)
  0.05
• Gilts
  0.066
• Beef 450 750 lb
  0.083
• Finishing
  0.078
• Beef cows
  0.10
• Dairy 50 lb milk/d
  0.087
• 70 lb milk/d
  0.096
• 100 lb milk/d
  0.11
• Dry
  0.074
• Heifers
  0.033
• Poultry Layers
  0.26
• Pullets
  0.20
• Broilers
  0.28
• Turkey
  0.23

40

• Availability of manure P to plants
• Affected by
• P retained during storage
• Type Proportion of excreted P
  available to apply
• Feedlot
  .95
• Manure under roof
  1.0
• Bedded swine
  1.0
• Liquid/slurry
  1.0
• Pit beneath slats
  1.0
• Compost
  .95
• Anerobic lagoon
  .35 (Remainder in sludge)
• P solubility in manure
• Greater in lagoon manure than solid or slurry
• Application method
• P retention greater from injection than surface
  application
• Soil
  incorporation Broadcast Irrigation
• -- of
  manure P available after application---
• Scraped manure 80
  70 -
• Poultry house litter 80
  70 -

41

• P uptake by crop
• - Based on realistic yield expectations
• 
  P2O5 uptake and harvest
• Corn
• Grain
  0.36 lb/bu
• Stover
  9.16 lb/ton
• Soybeans
  0.88 lb/bu
• Corn silage
  4.01 lb/ton
• Alfalfa hay
  10.08 lb/ton
• Alfalfa silage
  7.56 lb/ton
• Bromegrass hay
  9.62 lb/ton

42

• Calculation of manure application based on P
  needs
• Equations
• P2O5 needed, lb/ac RYE x P2O5 uptake and
  harvest
• Manure application, gal/ac P2O5 needed,
  lb/ac/(Manure P2O5 conc x
• 
  P
  availability)
• Example
• Field has a RYE for corn of 180 bu/acre
• Liquid manure containing 3.5 lb P2O5/1000 gal by
  analysis is applied with irrigation
• P2O5 needed, lb/ac 180 bu/ac x 0.36 lb P2O5/bu
  64.8 lb/ac
• Manure application, gal/ac 64.8 lb/ac /(3.5 lb
  P2O5/1000 gal .80)
• 
  23143 gal/ac
• Manure application rate for P will be 25 to 50
  of that for N
• Manure application should usually be based on the
  P rate
• New EPA regulations will allow a single
  application of manure to meet multiple year needs
  for P on fields with
• a low potential for run-off
• application does not exceed the N-based rate
  during the first year
• 
  

43

• Effects of using distillers grains for feeding
  cattle on land base for manure application
• Assumptions
• 2500 head feedlot with 2 groups per year
• Average weight, 975 lb
• lb P2O5/lb animal weight/year .078 (Corn based
  diet) or .156 (Distillers grains diet)
• Broadcast application 70 P availability
• ½ cropground available for land application
• Corn production, 200 bu/ac
• Corn P2O5 uptake .36 lb/bu

Corn, 1.9 miles
Distillers grains 2.7 miles