Transcript Persistence and Degradation of Herbicides in Rice, Maize

P. JANAKI
Herbicide Residue Chemist
DWSR Centre, Department of Agronomy,
Tamil Nadu Agricultural University, Coimbatore-641 003,
Tamil Nadu, India
e-mail: [email protected]
Introduction
Production Scenario in India
100
96.43
Area (m. ha)
Production (mi.tonnes)
80
60
43.81
40
15.09
20
7.89
8.72 8.85
0
Rice
Maize
Soybean
Crop
Productivity
(kg ha-1)
Rice
2203
Maize
1912
Soybean
1063
Herbicides Use in India
Non selective
field
4%
Plantation
6%
Soybean
4%
Maize
6%
Rice
17%
Others
6%
Wheat
57%
Herbicide - Indian market
Purpose
 Controlling weeds
 Increasing the yield crops
Herbicide residues concern
• Prone to leaching and contaminate soil and water
• Bioaccumulation in crop produce and food chain
• Health hazard to non target organisms
• Environmental safety
Residues status in major crops
Crop
Rice
Soybean
Maize
No of
locations
16
6
<MRL
>MRL
BDL
5
1
5
1
6
4
5
1
1
3
Objectives
 Study the persistence and degradation behavior of
commonly used herbicides in vertisols applied to
rice, maize and soybean crops.
Methodology
Experimental Details
Soil Properties
Rice soil
Maize soil
Soybean soil
Soil type
Clay loam
Sandy Clay
loam
Sandy Clay loam
Organic Carbon (g kg-1)
3.9
2.30
3.00
Available N (kg ha-1)
314
137
190
Available P (kg ha-1)
15.24
9.0
11.20
Available K (kg ha-1)
796
904
642
Infiltration rate (cm hr-1)
1.68
1.59
1.52
Bulk Density (g cm-3)
1.23
1.32
1.33
42
46
48
Porosity (%)
Treatments and methodology
Crops
Herbicides
Doses
Rice
Butachlor
X (1 kg ha-1)
2X (2 kg ha-1)
GC-ECD
86-88
Pretilachlor
X (1 kg ha-1)
2X (2 kg ha-1)
GC-ECD
82-84
Atrazine
X (1 kg ha-1)
2X (2 kg ha-1)
GC-FID
78-83
Alachlor
X (0.75 kg ha-1)
2X (1.50 kg ha-1)
GC-ECD
> 80
Pendimethalin
X (1 kg ha-1)
2X (2 kg ha-1)
GC-ECD
81-82
Metolachlor
X (0.75 kg ha-1)
2X (1.50 kg ha-1)
GC-ECD
> 80
Maize
Soybean
Determination
Recovery (%)
Results and Discussion
Initial deposition of applied herbicides
1.2
x
2x
1.003
Concentration (ppm)
1.0
0.8
0.658
0.6
0.4
0.658
0.486
0.530
0.426
0.328
0.214
0.402
0.324
0.212
0.2
0.0
RICE
MAIZE
SOYBEAN
0.316
0.5
Butachlor
0.5
0.4
y = 0.4709e-0.118x
R² = 0.9997
0.3
0.2
0.1
0.0
0
20
40
60
Concentration (ppm)
Concentration (ppm)
0.6
Pretilachlor
0.4
y = 0.4666e-0.062x
R² = 0.9257
0.3
0.2
0.1
0.0
0
0.4
0.3
0.3
0.2
0.2
0.1
0.1
0.0
100
1.0
Atrazine
y = 0.2578e-0.022x
R² = 0.936
0
25
50
75
100
Alachlor
0.8
y = 0.944e-0.164x
R² = 0.9527
0.6
0.4
0.2
0.0
0
Days after application
Metolachlor
0.4
y = 0.5566e-0.031x
R² = 0.9433
0.3
0.2
0.1
0.0
0
25
50
75
Days after application
100
Concentration (ppm)
0.5
0.5
20
40
Days after application
0.6
Concentration (ppm)
50
Days after application
Concentration (ppm)
Concentration (ppm)
Days after application
Pendimethalin
0.4
y = 0.4176e-0.045x
R² = 0.9689
0.3
0.2
0.1
0.0
0
50
Days after application
Field dissipation of applied herbicides in vertisols
100
Half-life
Herbicides persistence in the soil is expressed
as half life or time required for degradation of
fifty percent of the original molecule.
The persistence varies with the nature of a
chemical, soil and climatic conditions.
Persistence in Rice grown soil
Sampling
intervals after
herbicide
application
(Days)
Butachlor Residue (mg kg-1)
Sampling
intervals after
herbicide
application
(Days)
Pretilachlor Residue (mg kg-1)
x (1 kg/ha)
2 x (2 kg/ha)
0
0.214
0.486
0.300
15
0.096
0.246
0.020
30
0.058
0.189
45
0.020
0.058
BDL
0.005
BDL
90
BDL
BDL
60
90
BDL
BDL
0.014
BDL
Harvest
BDL
BDL
Harvest
BDL
BDL
x (1 kg/ha)
2 x (2 kg/ha)
0
0.328
0.658
10
0.194
20
30
0.007
BDL
45
Persistence in Soybean grown soil
Metolachlor - 0.75 kg/ha
0.8
Metolachlor - 1.50 kg/ha
0.6
0.4
0.2
0
0
10
30
45
60
90
95
Days after herbicide application
Persistence of metolachlor in soybean
grown soil
Concentration (ppm)
Concentration (ppm)
0.45
0.40
Pendimethalin - 1 kg/ha
0.35
Pendimethalin- 2 kg/ha
0.30
0.25
0.20
0.15
0.10
0.05
0.00
0
10
20
30
45
60
90
Days after herbicide application
Persistenence of pendimethalin in
soybean grown soil
Persistence in Maize grown soil
Sampling
intervals after
herbicide
application
(days)
Atrazine residue (ppm)
Sampling
intervals after
herbicide
application
Alachlor Residue (ppm)
X (0.75 kg/ha)
2X (1.50
kg/ha)
0
0.530
1.003
0.314
5
0.316
0.586
0.082
0.218
10
0.112
0.249
20
0.068
0.152
20
0.102
30
0.050
0.121
30
0.036
BDL
45
0.042
0.094
45
BDL
0.018
BDL
60
Harvest
BDL
BDL
0.052
BDL
60
Harvest
BDL
BDL
BDL
BDL
1.0 kg/ha
2.0 kg/ha
0
0.212
0.426
5
0.156
10
Degradation rate in rice soil
Degradation rate (%)
120
100
80
60
40
Butachlor
Pretilachlor
20
0
0
15
30
45
60
Days after herbicide application
Degradation of herbicides applied to rice soils
90
Degradation rate in maize soil
120
Alachlor
Atrazine
Degradation rate (%)
100
80
60
40
Half Life - 4.78
days for Alachlor
Half Life - 31.45
days for Atrazine
20
0
0
15
30
45
60
90
Days after herbicide application
Degradation of herbicides applied to maize grown soil
Harvest
Degradation rate in soybean soil
Degradation rate (%)
120
Pendimethalin
Metolachlor
100
80
60
40
Half Life -14.63
days for
pendimethalin
20
Half Life - 22.42
days for
metolachlor
0
0
10
20
30
45
Days after herbicide application
60
Degradation of herbicides applied to soybean
grown soil
Harvest
Optimized first order field dissipation curves
Herbicides
DT50
Goodness of fit
Butachlor – x
5.44
R² = 0.869
Butachlor – 2x
6.28
R² = 0.790
Pretilachlor – X
13.16
R² = 0.886
Pretilachlor – 2 x
11.72
R² = 0.923
Pendimethalin - x
13.24
R² = 0.828
Pendimethalin – 2x
16.02
R² = 0.837
Metolachlor – x
21.13
R² = 0.944
Metolachlor - 2x
24.71
R² = 0.957
Atrazine - x
30.81
R² = 0.714
Atrazine – 2 x
32.09
R² = 0.784
Alachlor – x
5.15
R² = 0.771
Alachlor – 2x
4.41
R² = 0.797
Rice
Soybean
Maize
Summary
 Initial deposits vary with the concentration applied
 Gradual and continuous dissipation was observed as a
function of time
 Dissipation followed the first order kinetics
 Half life increased with increase in concentration
 Mean half life of herbicides : 5.88, 12.44, 31.45, 4.78,
14.63 and 22.42 days for butachlor, pretilachlor, atrazine,
alachlor, pendimethalin and metolachlor