Additional Questions, Resources, and Moving Forward
Science questions raised in the development of a science assessment
Effect of Conservation Tillage
Systems on Dissolved Phosphorus
Gregory McIsaac
University of Illinois
&
Agricultural Watershed Institute
To what extent does conservation tillage
contribute bioavailable P to surface waters?
• Highly variable in time and space depending
on:
– Fertilizer quantity, placement and timing
– Soil characteristics and hydrology
Outline
• Surface P dynamics
• Relationships between soil P and runoff P
• plot studies
– Natural rainfall
– Simulated rainfall (sprinklers)
• Influence of surface runoff pathways
Dissolved P concentration in runoff
or drainage versus soil test P at surface
(Sharpley et al. 2003)
Higher leaching below30 cm
of dissolved P from manure
broadcast on no-till
compared to incorporated
manure
(Kleinman et al. 2009)
Stratification of soil test P in No-till (NT) vs Chisel Plow (CP)
with (+) and without (-) manure history (Andraski et al. 2003)
Manure history and long-term tillage effects on Bray P1–extractable soil P levels at
three depth increments (0–2, 2–5, and 5–15 cm) at Lancaster, Wisconsin, 2000.
Dissolved P load from No-till and Chisel Plowed 0.8 m2 plots
as a function of soil test P (Andraski et al. 2003)
Relationships between Bray P1–extractable soil P level (0–2 cm) and dissolved P loads in
long-term chisel plow and no-till systems at Lancaster, Wisconsin, 2000. P loads were lower
from No-till because of reduced runoff, rainfall was applied at 75 mm/hr for one hour.
Runoff from No-till and Chisel Plow as a function of soil residue cover
simulated rainfall event on 0.8m2 plots, 6th year of no-till
(Andraski et al. 2003)
Runoff from no-till (2nd & 3rd year) compared to other
tillage systems, Tama silt loam soil
40
no-till (short term)
35
tilled treatments
30
25
Runoff
from
65 mm
rainfall
(mm)
20
15
10 R² = 0.7452
5
0
0
20
40
60
80
100
Residue cover (%)
McIsaac et al. (1991)
Soluble P loss in runoff from 65 mm of
simulated rainfall
250
no-till (short term)
Soluble 200
P loss
from
150
65 mm
rainfall
(g P/ha) 100
tilled treatments
50
0
0
20
40
60
Residue cover (%)
(Data from McIsaac et al 1987)
80
100
(McIsaac et al. 1995)
Estimated fraction of surface applied P
fertilizer available to runoff and leaching
(Vadas et al. 2008)
Infiltration rates measured on long-term no-till (> 6 years)
and conventional tilled sites
100
90
80
Conv.
70
No-till
60
final
infiltration
50
rate
(mm/hr) 40
30
20
10
0
site 15 c
17 years
Silt loam
(Adapted from Savabi et al. 2008)
site 7
6 years
sandy loam
Site 11
6 years
silty clay loam
To till or not to till?
• Where no-till reduces runoff substantially,
dissolved P loads in runoff may be low despite
high concentrations
• P fertilizer and manure on the surface can be
vulnerable to runoff when and where no-till does
not reduce runoff significantly, such as
–
–
–
–
Coarser textured soils
Soils with high water table
Restricting subsurface layers
Frozen soils
Deep banding of P fertilizer reduced soil P at surface in 3 years
77 kg P per hectare applied
--------Distance from crop row------In row
19 cm
No-till
Broadcast P
Strip-till
Broadcast P
Strip-till
Deep banded P
†Indicate significant differences at P < 0.1;
(Fernandez and Shaefer 2011)
38 cm
57 cm
P soil survey 2007 & 2008
Soil sampled sites in regions with
high, medium and low
soil P supplying power
598 corn fields sampled
near end of growing season
(Fernandez et al., in press)
Surface to Subsurface Ratio for 547
Fields in Illinois
Organic
P
matter
Soil depth
(mg kg-1)
(%)
0-8cm
64 a
3.5 a
8-18cm
40 b
3.1 b
Ratio of Avg. values
1.6
1.1
Avg. of site ratios
2.4
1.2
Fernandez et al. (in press)
Spatial distribution of Soil P
0 to 18 cm (0 – 7 inches)
600
M e d iu m P S u p p lyin g P o w e r S o ils
B ra y P 1 S o il P h o s p h o ru s (m g k g -1 )
H ig h P S u p p lyin g P o w e r S o ils
500
400
L o w P S u p p lyin g P o w e r S o ils
7 % (1 4 fie ld s ) B e lo w C l
1 6 % (2 6 fie ld s ) B e lo w C L
3 4 % (6 0 fie ld s ) B e lo w C l
2 0 % (4 0 fie ld s ) M a in te n a n c e
-1
(1 5 -3 0 m g k g )
2 4 % (4 1 fie ld s ) M a in te n a n c e
-1
(2 0 -3 3 m g k g )
2 3 % (4 1 fie ld s ) M a in te n a n c e
-1
(2 3 -3 5 m g k g )
7 3 % (1 4 8 fie ld s ) A b o ve N o A p p l.P o in t
6 0 % (1 0 1 fie ld s ) A b o ve N o A p p l. P o in t
4 3 % (7 6 fie ld s ) A b o ve N o A p p l. P o in t
300
200
100
0
40
80
120
160
200
40
80
120
N u m b e r o f F ie ld s
Fernandez et al. (in press)
160
40
80
120
160
Standard natural rainfall soil erosion plots
uniform slopes, which minimize sediment deposition
http://www.cesperieni.ro/page3.html
Rainfall simulators increasingly used to study runoff and erosion processes
high intensity rainfall, water chemistry can influence results… useful for comparing different
systems and investigating processes but do not fully capture seasonal variations
http://www.ars.usda.gov/Research/docs.htm?docid=18093
Small plots do not generate rill erosion, or represent full hillslope hydrology
Results may be influenced by location on hill slope
http://www.ars.usda.gov/is/graphics/photos/oct01/k9572-1.htm
Fig. 5.3
Summary
P fertilizer applied to the soil surface is highly vulnerable to
loss in runoff during the first few weeks following application
Stratification of P at the soil surface contributes to high DRP
concentrations in surface runoff.
Conservation tillage reduces runoff at some locations (some times)
and this may mitigate against high DRP losses to runoff (although
could contribute to subsurface losses)
Subsurface placement of P fertilizer, such as in deep banding in Strip
Till, reduces stratification of P at the soil surface and probably
reduces DRP concentrations in runoff.
Plot studies need to be interpreted with a recognition that plots do
not fully capture seasonal or spatial variations in hill slope hydrology
or P dynamics.
Thank you!
No-till (years 1 and 2) vs. Chisel Plow on the contour,
Tama Soil
18
16
no-till
14
chisel
12
Runoff
10
from
47 mm
8
rainfall (mm)
6
4
2
0
fall
spring
(Daverede et al. 2003)