Transcript SUNDAY TIM CLASS ONE - Kansas State University

P Loss Pathways and Relative
Importance in Relation
to the P Index
Antonio Mallarino
Agronomy Department
Iowa State University
The Agronomic Perspective

P is an essential nutrient for crops.

P application may be needed to sustain
profitable crop production because
harvest removes P.

Soil-test P is above optimum levels for
crops in many crop production areas.

Soil-test P is very high in areas of
concentrated animal production.
Agronomic STP Interpretation Classes
NET RETURNS TO PHOSPHORUS
120
CORN
SOYBEAN
NET RETURNS ($/acre)
90
60
CORN
SOYBEAN
46 lb P2O5/acre
69 lb P2O5/acre
30
0
-30
-60
VL L O
0
10
20
H
VH
30
40
Interpretation
classes
50
VL L O
60 70
0 10
Bray-1 P (ppm)
20
H
VH
30
40
Interpretation
classes
50
60
70
Fertilizer P and Manure P

Nothing can justify P fertilization for
crop production in high-testing soils.

Manure application to high-testing
could be economically justified:
- disposal as waste
- N-based application

N-based application often results in soil
P buildup: continuous corn, poultry
manure, N-removal by soybeans.
The Environmental Perspective

P application in excess of crop needs
increase the risk of P loss from fields.

Soil P classes for crops cannot be used
as environmental risk classes when
economics of animal production is
considered.

How does soil-test P relate to P loss
from fields? What are the P transport
mechanisms and their importance?
What do we Know About P Loss?

Very complicated, and a function of

Source factors:
- soil P and other chemical properties
- P application rate, timing, and method
Transport factors:
- erosion, runoff, subsurface drainage
- rainfall intensity and duration
- distance to water body

Pathways for P Loss from Soils
• Soil erosion:
• Surface runoff:
• Subsurface
- gully
- infiltration excess
drainage:
- sheet and rill
- saturation excess
- tiles
- stream bank
- seepage
- coarse soil/subsoil
Precipitation
Precipitation
Infiltration
Precipitation
Tile Inlet
Seepage
Perched Water Table
Impermeable Layer
Receiving Water
Drainage Tile Flow
Saturated Soil
Extensive Ongoing Research
Plots Under Natural Rainfall
Plots Under Simulated Rainfall
Plots Under Simulated Rainfall
P Concentration in Runoff and Soil Test P
Total Dissolved P (ppm)
1.5
Optimum for crops
1.0
0.5
Exponential or linear increase?
But always increases!
0.0
0
20
40
60
80
Bray-1 Soil Test P (ppm)
100
120
DISSOLVED P - SOIL P RELATIONSHIPS ACROSS SOILS
1.6
Fayette
Nicollet
Marshall
Tama
Dissolved Reactive P (mg/L)
1.4
1.2
1.0
0.8
0.6
ALL SOILS
DRP = 0.07 + 0.002 M3
r ² = 0.92
0.4
0.2
0.0
0
100
200
300
400
Mehlich-3 P (mg/kg)
500
600
700
SOIL P EXTRACTANTS AND DISSOLVED P LOSS: NATURAL RAINFALL
1.6
Mehlich-3
1.4
Olsen
1.2
Agronomic P Tests
1.0
Total Dissolved P (mg/L)
0.8
0.6
0.4
0.2
0.0
0
20
40
60
80
Soil Test P (mg/kg)
100
0
10
20
30
40
50
Soil Test P (mg/kg)
60
1.6
Iron-Oxide Strip
1.4
1.2
Water
Environmental P Tests
1.0
0.8
0.6
0.4
0.2
0.0
0
10
20
30
40
50
Soil Test P (mg/kg)
60
0
5
10
15
20
Soil Test P (mg/kg)
25
Manure Rate, Incorporation, and P in Runoff
1 Day After Application
Bioav. P in Runoff (ppm)
4
10 Days After Application
4
Not incorporated
3
3
(R2 = 0.99)
2
2
Incorp (R2 = 0.96)
1
Not incorporated
2
(R = 0.94)
1
Incorp (R2 = 0.87)
0
0
0
10
20
30
40
Manure rate (kg P/ha)
50
0
10
20
30
40
Manure rate (kg P/ha)
A great deal of guessing!!
50
Soil-Test P and P Loss with Tile Drainage
0.14
Clarion-Webster and Kenyion-Clyde soil associations
Several fertilizer, swine and poultry manure rates
Two to three years
Three sites
Dissolved P (ppm)
0.12
0.10
Most Iowa subsoils
“filter” P from water
0.08
0.06
0.04
0.02
0.00
0
20
40
60
80
Bray-1 Soil P (ppm)
100
120
Vegetative Filter Strips
Soil P and P Loss: Watershed Scale Study
Clear Lake
Marshes, Parks
Urban
Figure 3: Clear Lake Total Phosphorus Results at Present Conditions for a 2" Rain
Modeled P Loss: Watershed Scale Study
10
4
3
Clear Lake
Ventura Marsh
1
8
7
5
9
6
2
11
AGNP S Sub-basins
Clea r Lake a nd Ve nt ura Marsh
Tota l Phosphorus (lbs)
0- 2
2 - 10
10 - 20
20 - 50
50 - 100
>10 0
N
ISU Limnology
W
E
S
0
3
6 Mile s
When do P losses occur in Iowa?

When there is soil erosion or water
loss!

Late February to June:
- High precipitation and snow melt
- Tilled soils
- Little or no crop canopy
- Low evapotranspiration
- Saturated soils (moisture, floods)
- Reduced conditions (soluble Fe+2)
Major P Loss from Cropland

Three major pathways:
- Erosion, particulate P: 1-35 lb P/acre?
- Runoff, dissolved P: 1-5 lb P/acre?
- Tiles, dissolved P: 0.1-1 lb P/acre?

Major factors:
- distance to stream, sediment transport
- P bioavailability in water bodies
Estimating Sediment Delivery
Bioavailability of Particulate
P in Water Bodies
Not treated
Killed bottom
digging fish
The P index

A comprehensive P assessment tool.

Very Low to Very High risk classes.

Assess what source and transport
factors dominate P delivery on a sitespecific basis.

Provide guidelines for P management
and soil conservation practices.

Also use other criteria (setbacks, avoid
short-term high losses, etc.).
Index Component
Factors
Gross Erosion
Sediment Trap/SDR
Buffer Factor
Enrichment Factor
STP Erosion Factor
6.7
1.0
0.7
1.2
1.1
Erosion
4.1
Runoff Factor
Precipitation Factor
STP Runoff Factor
P Application Factor
0.18
7.0
0.58
0.03
Runoff
Flow Factor
Precipitation Factor
STP Drainage Factor
Information
RUSLE erosion: 6.7 ton
Dist: 100 feet
Buffer: 66 feet
Tillage with buffer
Soil-test P: 106 ppm
RCN: 75
Hancock County
Soil-test P: 106 ppm
100 lb P 2O5/a; inc. within a week
0.8
1.0
7.0
0.1
Tile/Coarse Subsurface: Yes
Hancock County
Bray 1-P: 106 ppm
Subsurface 0.1
P- Index 5.0 High Risk Rating
IMPACT OF SOIL-TEST P AND SOIL EROSION
20
RISK
P INDEX VALUE
Erosion
VH
ton/a
1
2
5
10
15
15
15
10
10
H
5
2
5
M
1
L
VL
0
0 20
50
100
150
200
SOIL TEST-P (ppm)
250
300
A. Mallarino, ISU
I MPACT OF SOI L-TEST P AND WATER RUNOFF
15
RI SK
P I NDEX VALUE
% Runoff
1
15
30
50
50
10
H
30
15
1
5
M
2
0 20
50
100
150
200
SOI L TEST-P ( ppm)
250
300
Within-Field P-Index Based P Management
Soil Series
Slopes (%)
485
2-5
9-14
14-18
Erosion (ton/acre)
1.5
4.6
6.7
642
3.4
5-9
138
6.7
14-18
Soil-Test P (ppm)
P Index Rating
118
180
150
1.0 1.7
2.0
5.5
2.8
7.0
N-Based Manure?
Yes
??
??
106
74
1.3
10
5.0
Yes
No
Major P Loss Reduction in
High-Testing Soils:

Reduce soil erosion and
water runoff

Easy to do or regulate,
but not much gain by just
cutting P application