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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 Sampling Location Upper Slope
N Results and Discussion
457
455
Middle Slope
To assess the impact of slope position, soil
453
451
449 00
2,4-D half-lives ranged from 7 to 51 days (Figs. 2, 3
39
54
moisture and temperature on 2,4-D half-life
447
445 and 4). The total amount of 2,4-D mineralization at
443 546 825 0
441 Lower Slope N 103 days ranged from 5 to 51% (Figs. 2, 3 and 4).
in the plough layer. metres above
sea level
N
No
rth
ing Ea
stin
g
Canada
Manitoba
N
Figure 1. Site location, Deerwood,
Generally, 2,4-D mineralization was less at the
0 100 200 300 400
544 350
metres
546 865 0
Site Location
Manitoba, Canada
O
40 C temperature than at other incubation
Figure 1. Topography, and sampling locations, Deerwood, Manitoba,
Canada. temperatures.
Background and Significance
Soil Moisture
80 (% Field Capacity) Dry soils at 50% field capacity (FC) and excessively
[2,4-(dichlorophenoxy) acetic acid] is a herbicide Half-life (days) 70 Upper Slope wet soils at 125% FC demonstrated lesser 2,4-D
that is extensively used for the post-emergent 60 50 %
16 * mineralization than soils at 75% and 100% FC.
50 Soil Moisture (% of Field Capacity)
control of broadleaf weeds in agricultural crops. Soil 7 5 %
40
microorganisms are primarily responsible for the 30 27 18
1 0 0 %
Generally, 2,4-D half-lives increased from upper
34 20
biodegradation of 2,4-D in soil. The temporal and 20
31 32 39
46 12
21
slope < middle slope < lower slope positions.
37 41 1 2 5 %
10 5 °C 10 °C 2 0 °C 4 0 °C
spatial heterogeneity of soil moisture and 0
42 43 51
* percent 2,4-D
temperature within an agricultural field could affect 5 °C 10 °C 20 °C 40 °C mineralization at
Incubation Temperature 103 days
the diversity and abundance of 2,4-D degrading
Figure 2. 2,4-D half-lives as affected by
microorganisms and consequently 2,4-D soil moisture and temperature. 80 2,4-D Half-Life
persistence in soil. In addition, the effect of soil Middle Slope 12
Half-life (days)
70
Table 1. Soil characteristics at three 60
moisture content and temperature on 2,4-D 2,4-D half-life is here defined as
slope positions, Deerwood, Manitoba. 50
biodegradation in soil may vary with slope position 40
the amount of time (in days) that
Slope Position 12
Soil Characteristic 30
32 it takes for 50% of the
because of spatial variations in soil characteristics Upper Middle Lower 23 * 34 38 20
20 mineralizable fraction to be
34 37 31 36 39 31
(Table 1) and microbial populations. Texture SCL SCL SCL 10
36
45
46
degraded.
0
pH 6.2 5.5 7.7
5 °C 10 °C 20 °C 40 °C
Incubation Temperature
Field Capacity
42.5 43.9 31.8
(Volumetric %)
Methodology Organic Matter (%) 1.4 1.9 2.5
Figure 3. 2,4-D half-lives as influenced
80
by soil moisture and temperature.
-1 70 Lower Slope
Half-life (days)
Soil was obtained from three slope positions (upper, Kd (mL g ) 1.2 2.0 3.2
60
5
middle and lower) from an undulating landscape 50
24 12
near Deerwood, Manitoba, Canada (Fig. 1). Implications 40
9 13
30 33
31
Microcosm incubation experiments using 14C ring- 20
35
Soil moisture and temperature influenced 2,4-D half-lives and are 22 * 39 42 41 36 45 43 43
labelled 2,4-D were conducted at four different soil important factors affecting 2,4-D persistence in soil.
10
na
§
0
moisture contents (50, 75, 100, 125% of field 5 °C 10 °C 20 °C 40 °C
O
capacity) and four temperatures (5, 10, 20, 40 C) to An improved understanding of the effect of soil moisture and Incubation Temperature
temperature fluctuations and their interaction on 2,4-D fate could
assess the mineralization of 2,4-D over 103 days Figure 4. 2,4-D half-lives as affected by
enhance pesticide fate modeling at the landscape scale.
using a factorial experimental design. soil moisture and temperature § data not available
For more information contact: Travel funds provided by: U of M SiGPAC and
Janna Shymko: umwils46@cc.umanitoba.ca U of M Faculty of Graduate Studies
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