Ef fect of Landscape Position, Soil Moisture and Temper ature
on 2,4-D Half-Life
Janna Shymko and Annemieke Farenhorst
Department of Soil Science, University of Manitoba, Winnipeg, Manitoba, Canada
Objective
N
Upper Slope
Sampling Location
Results and Discussion
457
455
449
54
447
443
39
00
546 825 0
441
Lower Slope
N
metres above
sea level
100
0
No
200
rth
ing
Ea
stin
Canada
g
N
N
Manitoba
546 865 0
Generally, 2,4-D mineralization was less at the
O
40 C temperature than at other incubation
temperatures.
Figure 1. Site location, Deerwood,
Manitoba, Canada
400
300
metres
Background and Significance
2,4-D half-lives ranged from 7 to 51 days (Figs. 2, 3
and 4). The total amount of 2,4-D mineralization at
103 days ranged from 5 to 51% (Figs. 2, 3 and 4).
451
445
544 350
Site Location
Figure 1. Topography, and sampling locations, Deerwood, Manitoba,
Canada.
Soil Moisture
80
Half-life (days)
60
50
16
*
50 %
Soil Moisture (% of Field Capacity)
7 5 %
40
1 0 0 %
34
46
31 32
37 41
10
Soil was obtained from three slope positions (upper,
middle and lower) from an undulating landscape
near Deerwood, Manitoba, Canada (Fig. 1).
Microcosm incubation experiments using 14C ringlabelled 2,4-D were conducted at four different soil
moisture contents (50, 75, 100, 125% of field
O
capacity) and four temperatures (5, 10, 20, 40 C) to
assess the mineralization of 2,4-D over 103 days
using a factorial experimental design.
20
12
39
21
1 2 5 %
5 °C
42 43 51
5 °C
10 °C
20 °C
Incubation Temperature
Table 1. Soil characteristics at three
slope positions, Deerwood, Manitoba.
Slope Position
Upper Middle Lower
Texture
SCL
SCL
SCL
pH
6.2
5.5
7.7
42.5
43.9
31.8
1.4
1.9
2.5
1.2
2.0
3.2
(Volumetric %)
Organic Matter (%)
-1
Kd (mL g )
2 0 °C
4 0 °C
mineralization at
103 days
40 °C
Figure 2. 2,4-D half-lives as affected by
soil moisture and temperature.
Soil Characteristic
10 °C
* percent 2,4-D
0
Field Capacity
Methodology
Generally, 2,4-D half-lives increased from upper
slope < middle slope < lower slope positions.
18
27
30
20
Dry soils at 50% field capacity (FC) and excessively
wet soils at 125% FC demonstrated lesser 2,4-D
mineralization than soils at 75% and 100% FC.
(% Field Capacity)
Upper Slope
70
80
Half-life (days)
[2,4-(dichlorophenoxy) acetic acid] is a herbicide
that is extensively used for the post-emergent
control of broadleaf weeds in agricultural crops. Soil
microorganisms are primarily responsible for the
biodegradation of 2,4-D in soil. The temporal and
spatial heterogeneity of soil moisture and
temperature within an agricultural field could affect
the diversity and abundance of 2,4-D degrading
microorganisms and consequently 2,4-D
persistence in soil. In addition, the effect of soil
moisture content and temperature on 2,4-D
biodegradation in soil may vary with slope position
because of spatial variations in soil characteristics
(Table 1) and microbial populations.
Middle Slope
70
2,4-D Half-Life
12
60
2,4-D half-life is here defined as
the amount of time (in days) that
it takes for 50% of the
mineralizable fraction to be
degraded.
50
40
20
10
12
32
30
23
*
34 37
31 36 39
20
38
34
46
36
31
45
0
5 °C
10 °C
20 °C
40 °C
Incubation Temperature
Figure 3. 2,4-D half-lives as influenced
by soil moisture and temperature.
Implications
Soil moisture and temperature influenced 2,4-D half-lives and are
important factors affecting 2,4-D persistence in soil.
An improved understanding of the effect of soil moisture and
temperature fluctuations and their interaction on 2,4-D fate could
enhance pesticide fate modeling at the landscape scale.
For more information contact:
Janna Shymko: [email protected]
80
Half-life (days)
To assess the impact of slope position, soil
moisture and temperature on 2,4-D half-life
in the plough layer.
Middle Slope
453
Lower Slope
70
60
5
50
12
24
40
9 13
30
20
10
0
31
*
35
33
39 42 41
22
§
36 45 43 43
na
5 °C
10 °C
20 °C
40 °C
Incubation Temperature
Figure 4. 2,4-D half-lives as affected by
§ data not available
soil moisture and temperature
Travel funds provided by: U of M SiGPAC and
U of M Faculty of Graduate Studies