Embed Size (px)
Citation preview
Using the Missouri P index
John A. Lory, Ph.D.
Division of Plant Sciences
Commercial Agriculture Program
University of Missouri
Many streams and lakes are phosphorus limited.
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
0 25 50 75 100 125 150 175 200
Total Phosphorus (ppb)
Ozark HighlandsOthers
Jones and Knowlton 1993
Wat e
r C
lari
ty a
s m
easu
r ed
by
Secch
i d
ep
th (
m) Missouri reservoirs
Challenge:
Where,
when,
and how to apply manure
to minimize P loss to surface
water.
Nutrient planners are required to assess phosphorus loss on all fields receiving manure.
LowN-based Applications
MediumN-based Applications
HighP-based Applications
VeryHigh
No Manure Applications
Phosphorus Loss Assessment
You choose the method
Agronomic soil test recommendation Objective: does the crop need P?
Phosphorus threshold
Phosphorus Index Objective: will applied P be vulnerable to
losses?
Missouri’s approach: 2 choices
Agronomic soil test recommendation Objective: does the crop need P?
Phosphorus threshold
Phosphorus Index Objective: will applied P be vulnerable to
losses?
Soil testing objective
Determine crop needs for phosphorus
(P) to maximize yield.
0
1
2
3
4
5
6
7
0 10 20 30 40 50
Soil Test P (lb acre-1)
Dry
Matt
er
(g
)
Critical value = 43 lb/ac
Soil test P
Yie
ld
Low Medium High Very High
Critical Value
Soil testing objective
The “critical value” is the lowest soil test
level where no response to fertilizer is
expected.
Soil test P
Low Medium High Very High
Critical Value
Soil testing objective
Critical soil test P
= 40 or 45 lbs P/acreY
ield
Soil testing objective
Critical soil test P
= 40 or 45 lbs P/acre
Soil test P
Yie
ld
Low Medium High Very High
Critical Value
Buildup Maintain NoneFertilizer Rec.:
LowN-based Applications
MediumN-based Applications
HighP-based Applications
VeryHigh
No Manure Applications
Soil test P
Yie
ld
Low Medium High Very High
Critical Value
Buildup Maintain NoneFertilizer Rec.:
Soil test P
Yie
ld
Low Medium High Very High
Critical Value
Buildup Maintain NoneFertilizer Rec.:
Missouri’s approach: 2 choices
Agronomic soil test recommendation Objective: does the crop need P?
Phosphorus threshold
Phosphorus Index Objective: will applied P be vulnerable to
losses?
Runoff volume Method of application Time since application Application rate Soil test P Soil type Cultivation Vegetative cover
Factors affecting runoff of P
P indexes are state specific.
Index Target:
- Runoff- Irrigation
- Runoff- Irrigation Long-term
Runoff
- Runoff- Leaching
P indexes are state specific.
Approach:
Multiplicative tabular factors
Simplified model
Additive tabular factors Simplified
model
Do Differences Between StatesMake Sense?
?
P index developed cooperatively by MU and NRCS.
Based on best professional judgment.
Available as a spreadsheet at: http://nmplanner.missouri.edu/
Missouri P index objectives
Strategic planning tool for use in writing a 5-year nutrient management plan.
Identify fields where field characteristics are likely to result in high P loss in runoff.
Simple to use with readily available information for people with an NRCS conservation plan.
6 Factors in the Missouri P index Soil test result
include units and sampling depth Tillage
Tilled vs. notill and forages RUSLE estimate of erosion Land cover Soil hydrologic group
A, B, C or D Distance from water feature
Simple model approach
Sediment P Function of RUSLE-2 erosion, soil test P
and sediment delivery ratio.
Soluble P Function of runoff volume (curve number
approach) and soil test P.
Higher standard in the clear-water region of the state.
P index rating system
Rating Clear-water region Other
Low <1 <3
Medium >1 and <5 >3 and <7
High >5 and <10 >7 and <12
Very High >10 >12
Higher standard in the clear-water region of the state.
Surface applications require a tactical tool. Educational tools being developed to identify
times of year runoff least likely
Inputs: Ground cover - County Soil hydrologic group - Soil condition Soil moisture
Output Evaluation of runoff risk (low, medium, high) Predicted rainfall amount needed to initiate
runoff
Future
P index integrated into RUSLE 2
Email notification system to help evaluate timing of manure applications.
