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
Al, Fe
Ca
Optimum pH
4-5
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:
– Soil pH
» Greatest at pH 6 – 7
– Soil P concentration
» Increases with very high soil P concentrations
• 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 Carbon:Phosphorus ratios
– Greatest at C:P ratios > 300:1
• 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
FORMS OF PHOSPHORUS IN SOIL
P FERTILITY
• Discussed as P2O5
– Calculated by multiplying P by 2.29
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
P TRANSPORT IN THE ENVIRONMENT
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)
Streams not discharging into lakes .10 mg/l (100 ppb)
P CONCENTRATION IN IOWA LAKES (2001)
CHANGE IN THE CONCENTRATION OF P IN
MAN-MADE LAKES IN IOWA
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
• The low N:P ratio of manure relative to crop needs
– Crop
N:P2O5 needed
Livestock N:P2O5 excreted N:P2O5 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
• Low P retention
% retained
Growing cattle
Growing swine
Poultry
21
27
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
FUNCTIONS OF P IN LIVESTOCK
• Bone structure
– 80% of the body’s P
– Bound to calcium as hydroxyapatite crystals
• Ca10 x(PO4)6(OH)2(H3O)2x
– Ca:P ratio = 2:1
– 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
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 (< .2%P)
for long periods of time
– May be the result of impaired feed digestion by not meeting
the microbial needs
P IN FEEDS
• P concentration in feeds
– P concentration in most feeds except mature forages is moderate
to high.
Livestock species Total P reqt. %
Dairy cow
Lactating
.40
Dry
.25
Beef
Finishing steer
.24
Lactating cow
.22
Dry cow
.12
Swine
Growing-finishing
.4 - .6
Sow
.6
Poultry
Layers
.4
Broilers
.4
Turkeys
.6
Feed class
Feed
P, %DM
Energy conc Corn
.30
Oats
.40
Cottonseed
.60
Protein conc Soybean meal .71
Meat and bone 4.73
Grain
Wheat mids
1.02
processing
Distillers grains .83
byproducts
Corn gluten feed1.00
Forages
Corn silage
.28
Alfalfa hay
.31
Grass hay
.30
Grass pasture .40
Corn stalks
.09
• 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
– P availability
Corn and corn byproducts
Wheat
Soybean meal
Meat and bone meal
Forages
Dicalcium phosphate
Defluorinated phosphate
Swine and poultry
(% available)
15
50
25
67
100
95
Cattle
70
70
70
64
70
70
• Must compensate for the low availability of phosphorus from
plant sources in monogastrics by supplementing mineral
sources
– Results in increase P excretion
P DIGESTION AND METABOLISM IN NONRUMINANTS
Small intestine
Phytate-P
(60-75% of plant P)
Excess Ca or high pH
Feces
Inorganic P
Passive
absorption
Active
transport
Circulating P
+
1,25(OH)2vitamin D
kidney
(Low blood Ca or P)
Bone
Soft tissue
Excess
25 (OH) vitamin D
(Circulating in blood)
Liver
Kidney
Urine
Vitamin D
(Diet or sunlight)
• Factors affecting P absorption from the gut
– Phytate
• High phytate reduces P absorption
– Ca:P ratio
• Ca:P should be between 1:1 to 1.25:1
– Intestinal pH
• High intestinal pH reduces P absorption
– Vitamin D
• Vitamin D deficiency reduces P absorption
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 <4.0
– 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
– 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
Normal diet
Phytase-treated
% P in phases Manure P (lb P2O5/yr)
.60, .55, .50, .45
13,000
.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
• 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
Corn
Soybeans
Phytate-P, % of total P
Normal
Low phytate
75
35
70
24
• Increases P bioavailability
P bioavailability, %
Normal
Low phytate
Corn
22-33
46-77
– Feeding low phytate corn and soybean meal may reduce P excretion by
50% when diets balanced for available P
• Effects of low phytate crops and phytase on P excretion are additive
• 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
• Balance diets closer to the P requirements
– Limit safety margins
• Swine industry commonly feeds P at 120 – 155% of the NRC
requirements
Swine diet
.5% P
.6% P
Manure P, lb/pig
2.5
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 > 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
– 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
P DIGESTION AND METABOLISM IN RUMINANTS
Rumen
Phytate-P
Inorganic-P
Small intestine
Undegraded
Degraded
Feces
(95-98% of
excreted P)
Very little
Inorganic P
Microbes
Passive
absorption
Active
transport
+
Circulating P
Recycled to digestive
tract via saliva
(Supplies P to rumen
microbes if diet is deficient;
80% of total P excreted)
1,25(OH)2vitamin D
kidney (Low Ca
or P)
Bone
25(OH)vitamin D
Soft tissue
liver
Excess
Kidney
Excreted (Very little)
Vitamin D
(Diet or sunlight)
FACTORS AFFECTING P ABSORPTION IN RUMINANTS
• Amounts of P consumed
– High P intake reduces P absorption
• Ca:P ratio
– Optimum is 2:1
• 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
STRATEGIES TO REDUCE PHOSPHORUS
LOADING OF THE ENVIRONMENT BY RUMINANTS
• Do not overfeed P
– Dairy
% P in DM Manure P, lb/cow/lactation
.52
64.9
.32-.42
42.2
.35
34.8
.25
-
Industry average
NRC requirement
Adequate
Dry cow
• 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
– 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 .5%P vs. .4%P
– 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
Wheat mids
Distillers grains
Corn gluten feed
P, % DM
1.02
0.90
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
• 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 < condition score 5, analyse diet for energy, protein
and minerals
– P solubility in feces
• No soluble P means inadequate P in diet
• 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.
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)
MANURE HANDLING AND STORAGE TO
MINIMIZE P LOADING OF THE ENVIRONMENT
• Goals
– Maintain N:P 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
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?
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
– 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
– 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 (> 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.
CALCULATION OF MANURE APPLICATION RATE
BASED ON THE AGRONOMIC RATE FOR P
• Manure P production or concentration
Swine
Beef
Dairy
Poultry
Manure_________
Growing-finishing
Sows & litter
Sows (gestation)
Gilts
450 – 750 lb
Finishing
Beef cows
50 lb milk/d
70 lb milk/d
100 lb milk/d
Dry
Heifers
Layers
Pullets
Broilers
Turkey
P2O5, lb/lb animal wt/yr
0.13
0.12
0.05
0.066
0.083
0.078
0.10
0.087
0.096
0.11
0.074
0.033
0.26
0.20
0.28
0.23
• 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
Liquid manure (slurry)
80
70
70
Anerobic lagoon liquid
90
80
80
•P uptake by crop
- Based on realistic yield expectations
P2O5 uptake and harvest
Corn
Grain
Stover
Soybeans
Corn silage
Alfalfa hay
Alfalfa silage
Bromegrass hay
0.36 lb/bu
9.16 lb/ton
0.88 lb/bu
4.01 lb/ton
10.08 lb/ton
7.56 lb/ton
9.62 lb/ton
• 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
• 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