The Georgia P-Index - USDAGeorgia P Index Categories Add conservation practices or reduce P...
Transcript of The Georgia P-Index - USDAGeorgia P Index Categories Add conservation practices or reduce P...
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The Georgia P-Index
Miguel Cabrera/David RadcliffeCrop & Soil SciencesUniversity of Georgia
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Overview
Regulatory backgroundPhosphorus and water qualityPhosphorus in soilPhosphorus in manuresPathways for P lossDetermining the risk of P loss
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Regulatory BackgroundNew state regulations require that CNMPs meet NRCS standardsStarting Fall 2001, NRCS standard requires:
considering risk that P loss from a field receiving manure will reach sensitive watersif risk is high, reduce manure application rate or use BMP’s to reduce risk
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Phosphorus and Water QualityEutrophication: natural aging of lakes and streams due to nutrient enrichmentIncreased aquatic weeds, algal growth, low oxygen levels, fish kills, and bad-
tasting water (geosmin)High levels of nutrients cause acceleratedeutrophicationLakes are more sensitive than streamsFresh water more sensitive to P than N
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Natural Process Accelerated by land use
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Phosphorus and Water Quality
Tulsa, OK filed suit in December 2001 against 6 poultry processorsProcessors have farms in the watersheds of two lakes (Eucha and Spavinaw) which supply drinking water to TulsaTaste and odor problems caused by algal growthTulsa spent > $4 million to correct problem
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Phosphorus in Soil
Fe, Alhydrousoxides
PP P PPP
P
P
PP P
PP
P
P
P
P
PP
PP P
P
P P
P
PP
P
P
PP
P
PP
P
P
P
P
Root hair
Time after P application
P
P
PP
P
P
P
P
P
P
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Phosphorus in Runoff
Soil Test P (Mehlich 1, lb P/A, 0-4 inches)0 100 200 300 400 500
Run
off D
RP
(mg
P L
-1)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
DRP = 0.17 + 0.0016 STPr2 = 0.57
Schroeder et al., 2002
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Pastures/Hayfields
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Agronomic Crops
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Phosphorus in Manures
Overapplication of P with inorganic fertilizers is unlikely because of cost
Over-application of P with manures is very likely because of N/P ratio
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Phosphorus in Manures
Crops need N/P = 88 lbs N/1 lb P
Broiler litter has N/P = 1.2 8 lbs N/6.7 lbs of P
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Phosphorus in ManuresIn Georgia, most of the broiler litter is surface-applied to grasslands
Manure on the soil surface is exposed to surface runoff
P in runoff from grasslands is controlled by P on the soil surface
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Pathways for Phosphorus Loss
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Determining the Risk of P Loss
Georgia task force appointed with NRCS, ARS, and University personnel
Decided to use P-index
P-Index takes SOURCE and TRANSPORT factors into account
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Sources of PhosphorusSoil P (soil test P – lb/A)Fertilizer P
Rate (lb P2O5/A)Method of application (banded, incorporated, or surface applied)
Organic P (lb P2O5/A)Rate (lb P2O5/A) Type of organic P (poultry, dairy, or swine – fresh manure, litter, or slurry)Method of application (banded, incorporated, or surface applied)
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Transport of Phosphorus
Surface runoff (curve number)
Leaching (hydrologic soil group)
Erosion (ton/A/year)
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BMP’s to Reduce P Losses
Alter feed ration to reduce P in manureAdd alum to reduce soluble P in manureDon’t apply manure when runoff is likelyIncorporate or inject manuresAvoid artificially drained fieldsUse grass filters and stream-side buffersUse practices that reduce runoff and erosion
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Georgia P Index Categories
Add conservation practices or reduce P applications to achieve a P Index < 100 in the short term. Develop a management plan with the goal of achieving a P Index < 75 within 5 years.
VeryHigh
100 or greater
Add conservation practices or reduce P applications to achieve a P Index < 75.
High75 to <100
Use conservation practices and P applications that maintain a P Index < 75.
Medium40 to <75
N-based NMP is usually satisfactory.Low0 to <40
InterpretationCategoryP index range
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Example: Broiler LitterHay fieldSources of P
Soil test P = 450 lb/A5 tons broiler litter/A in Dec & Feb (300 lb P2O5/A)
TransportCurve number = 70Hydrologic group = BErosion = 0.1 ton/A/yearDepth to water table = 15 ft
BMP’sNo vegetated buffer
Result = 89 (high – reduce below 75)
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Example: Broiler Litter
Add a buffer5 ft of vegetated bufferSoil test P of buffer = 250 lb P/AResult = 72 (medium – OK)
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Example: Broiler Litter
Change application timeNov & March instead of Dec & FebResult = 74 (medium – OK)
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P INDEX VALUE0 20 40 60 80 100 120 140
AN
NU
AL
P L
OS
S (
kg P
/ha)
0
2
4
6
8
10
12
14P Loss Versus P-Index Value
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Future ImprovementsIdentify field by:
County (rain)Soil series (hydrologic group, runoff P vs STP)Management (runoff, erosion)
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SummaryP can accelerate eutrophicationManures applied based on N supply lead to a buildup of soil PSoil P can be lost through runoff and leachingRisk of P loss can be assessed with the P-IndexBMP’s can be used to reduce P-Index value