movement of surface-applied phorate and water through unsaturated soil
TRANSCRIPT
Agro-Ecosystems, 8 (1983) 25*263 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
259
Short Communication
MOVEMENT OF SURFACE-APPLIED PHORATE AND WATER THROUGH UNSATURATED SOIL
G. SINGH, Z. SINGH, IS. DAHIYA and R.S. MALIK
Department of Entomology, Haryana Agricultural University, Hissar 125004 (India)
(Accepted 9 June 1982)
ABSTRACT
Singh, G., Singh, Z., Dahiya, I.S. and Malik, R.S., 1983. Movement of surface-applied phorate and water through unsaturated soil. Agro-Ecosystems, 8: 259-263.
The simultaneous movement of surface-applied phorate and water was studied in labo- ratory columns containing, initially, moist and dry sandy loam soil. Phorate was applied onto the soil and leached with water under ponded and controlled infiltration conditions. Phorate and water distribution profiles were determined by destructive sampling at two stages: (1) immediately following infiltration and (2) after matching total infiltration, re- distribution and evaporation time for two water-application rates. Regardless of the initial soil water content, just after the termination of infiltration, phorate was displaced more efficiently and its concentration peak formed at deeper depth with the slower than with the faster application rate. Following redistribution, this trend was reversed. Phorate move ment was also found to be dependent on the initial soil water content. The higher the ini- tial soil water content, the deeper and more complete was the displacement of phorate during infiltration and redistribution.
INTRODUCTION
The simultaneous movement of water and pesticides through unsaturated soils is a subject of practical importance for the protection of crops and the environment. Some soil-applied pesticides leach through the root-zone to the sub soil and underground water. Several reports suggest that displacement of chemicals in unsaturated soils is dependent on the rate of water application (Kirda et al., 1974; Wood and Davidson, 1975; Dahiya et al., 1980). Some workers have demonstrated that transport of a chemical under such condi- tions is independent of the initial soil water content (Warrick et al., 1971; Ghuman et al., 1975); others have concluded the converse (Singh et al., 1979; Dahiya et al., 1980).
MATERIALS AND METHODS
Lucite plastic cylinders (90 cm long, 5 cm ID) were packed with air-dried or moist Hissar sandy loam - Typic comborthids (0.48% OM; 65% sand; 12%
0304-3746/83/0000-0000/$03.00 0 1983 Elsevier Scientific Publishing Company
TAB
LE I
Sum
mar
y of
exp
erim
enta
l co
ndit
ions
an
d re
sult
s
Exp
eri-
Initi
al
Ave
rage
A
vera
ge
men
t so
il w
ater
in
filtr
a-
wat
er
appl
ica-
ti
on
cont
ent
tion
(h
) B
0 (cm
’ ra
te V
cm
-‘)
(cm
h-’
)
1.1
0.01
8 1.
4 5
1.2
0.01
8 1.
4 5
1.3
0.01
8 1.
4 5
1.4
0.01
8 1.
4 5
2.1
0.14
1.
4 5
2.2
0.14
1.
4 5
2.3
0.14
1.
4 5
2.4
0.14
1.
4 5
3.1
0.01
8 0.
12
55
3.2
0.01
8 0.
12
55
3.3
0.01
8 0.
12
55
3.4
0.01
8 0.
12
55
4.1
0.14
0.
12
55
4.2
0.14
0.
12
55
4.3
0.14
0.
12
55
4.4
0.14
0.
12
55
“c =
con
trol
led;
FP
= f
ree
pond
ing.
Red
istr
ibut
ion
Tota
l W
ater
W
etti
ng
Ave
rage
D
epth
R
ecov
ery
tim
e ti
me
for
appl
ica-
fr
ont
wat
er
to
(%)
(h)
infil
tra-
ti
on
dept
h co
nten
t co
ncen
tra-
ti
on
patt
erna
(c
m)
abov
e ti
on
plus
w
etti
ng
peak
re
dist
ri-
fron
t (c
m)
buti
on
(cm
3 cm
-%)
(h)
0 5
FP
19
0.27
13
10
0.00
16
3 16
8 FP
25
0.
19
21
79.3
5 35
5 36
0 FP
29
0.
13
25
76.0
9 71
5 72
0 FP
39
0.
09
27
33.7
0 0
5 FP
25
0.
26
19
100.
00
163
168
FP
35
0.19
27
93
.18
355
360
FP
41
0.14
31
82
.55
715
720
FP
49
0.11
39
77
.75
0 55
C
21
0.
25
17
100.
00
113
168
c 31
0.
17
18
77.8
3 30
5 36
0 C
33
0.
16
21
59.6
8 66
5 72
0 C
39
0.
10
24
46.7
4 0
55
C
27
0.32
21
10
0.00
11
3 16
8 C
33
0.
27
24
78.4
9 30
5 36
0 C
37
0.
23
29
62.0
0 66
5 72
0 C
47
0.
16
32
59.8
9
261
silt; 21% clay; pH 8.00; EC 0.17 mmhos cm-‘; CEC 10.9 meq/lOO g). A bulk sample of surface soil (O-l 5 cm) was collected from a field located at the H.A.U. farm Hissar, India, air-dried and passed through a 2-mm sieve. The average bulk density of the columns was 1.62 g cmw3. The distal end was closed by a rubber cork supporting the sample but permitting air exchange through a hole. Phorate (THIMET); O,O-diethyl-S-(ethylthio) methyl phos- phorodithioate, a systemic organophosphorous insecticide (water solubility, 50 p.p.m.), was used as the test material. Technical grade phorate (93.37%) was obtained through the courtesy of Cynamide India Ltd., Bombay, India. Phorate (785 pg per column) was spread evenly on the soil surface. The essential features of the treatments and experimental results are presented in Table I. The treatments included two water-application rates during infiltration (ponded and controlled) and two initial soil water content levels, the higher being approximately 22% of saturation, and the smaller corresponding to air dryness.
For the ponded treatment, water was added by maintaining a constant depth of 4 cm at the soil surface through a mariotte bottle arrangement and for the steady infiltration treatment (controlled), water was applied through a sintered glass funnel slowly enough to avoid ponding on the soil surface. After 6.5 cm of water had infiltrated, leaching was stopped. Phorate and water profiles were determined by destructive sampling at two stages: (1) immediately after infiltration; and (2) when the infiltration plus redistribu- tion time was equal for the two water-application rates involved. During redistribution, columns were placed in 85-cm deep auger holes outside the laboratory so as to simulate the field conditions for evaporation. Water con- tent was determined gravimetrically by oven-drying a portion of the soil sam- ple. The remainder of the sample was used for the determination of total phorate residues in the soil using redistilled dichloromethane as the solvent. Analysis for phorate residues was carried out following the calorimetric method developed by Getz and Watts (1964).
RESULTS
The solute concentration peak for Experiment 1.1 (Fig. 1) was nearer the surface than in the other experiments. Spreading was slightly less after ponding than after controlled infiltration, indicating less movement for higher water-application rates.
In Experiments 1.3 and 3.3 the residue concentration node was deeper for ponding than for controlled infiltration; the converse of Experiments 1.1 and 3.1. This may be because with ponded application the solute may not approach adsorption equilibrium as quickly as during controlled applica- tion, or it may result from different proportions of phorate degradation pro- ducts in the two treatments.
The initial soil water content prior to commencement of infiltration appreciably affected the resulting total phorate residue (TPR) distribution.
.
i
Fig. 1. TPR and water content profiles after displacement of surfaceapplied phorate with 6.5 cm of water in air-dry sandy loam soil (0, = 0.018 cm” cme3) following an infiltration period of 5 (Experiment 1.1) and 55 h (Experiment 3.1) and a redistribution period of 355 (Experiment 1.3) and 305 h (Experiment 3.3).
Irrespective of water-application rate, the post-infiltration wetting front depth and depth of the TPR concentration peak were greater in soil that was initially moist than in initially dry soil (Table I, Figs. 1 and 2), possibly because insecticide may have moved preferentially through large pores (mobile) and by-passed the small pores or it may be attributed to the deep penetration of water and TPR during infiltration of initially moist soil.
The results of this study may be helpful for developing means of in- creasing the efficiency and decreasing the groundwater pollution hazards of surface-applied insecticides of this group. For instance, under irrigated humid conditions, it is important to reduce loss by leaching. In such situa- tions, it is better to apply water to a crop under controlled irrigation condi- tions and when the soil is relatively dry so that a major portion of the insec- ticide is left confined to shallower depths. In arid and semi-arid regions, it may be useful to place the insecticide deep so that when the soil dries, it will not evaporate. This may be accomplished by ponding when the soil is moist.
263
PHORATE CONTENT (,,q,q> WATER CONTENT (7.)
0 02 04 06 0.0 1.0 12 t 4 16 5 10 15 20 0-1
25 I I I r1 I
28 - i 1: :
32 - --._ “‘_, ___--- IL
__-- ,’
i 36-
f ’ i EXPT 1,
-A- 2 1 ? 40 - El --,-- 2.3 >’
c t =1.4cmh;’ i
Fig. 2. TPR and water content profiles after displacement of surfaceapplied phorate with 6.5 cm of water with a velocity i of 1.4 cm he’ in moist sandy loam (0, = 0.14 cm3 cmm3) following an infiltration period of 5 h (Experiment 2.1) and infiltration plus redistribu- tion period of 360 h (Experiment 2.3).
REFERENCES
Dahiya, I.S., Singh, M., Singh, M. and Hajrasuliha, S., 1980. Simultaneous transport of surface-applied salts and water through unsaturated soils as affected by infiltration, redistribution and evaporation. Soil Sci. Sot. Am. Proc., 44: 223-228.
Getz, M.E. and Watts, R.R., 1964. Application of 4 (p-nitrobenzyl) pyridine as a rapid quantitative reagent for organophosphate pesticides. J. Assoc. Off. Anal. Chem., 47 : 1094-1096.
Ghuman, B.S., Verma, S.M. and Prihar, S.S., 1975. Effect of application rate, initial soil wetness and redistribution time on salt displacement by water. Soil Sci. Sot. Am. Proc., 39: 7-10.
Kirda, C., Nielsen, D.R. and Biggar, J.W., 1974. The combined effects of infiltration and redistribution on leaching. Soil Sci., 117: 323-330.
Singh, M., Dahiya, I.S. and Singh, M., 1979. Simultaneous transport of surface applied salts and water through unsaturated soils during infiltration and redistribution. Commun. Soil Sci. Plant Anal., 10: 591-611.
Warrick, A.W., Biggar, J.W. and Nielsen, D.R., 1971. Simultaneous solute and water transfer for an unsaturated soil. Water Resour. Res., 7: 1216-1225.
Wood, A.L. and Davidson, J.M., 1975. Fluometuron and water content distribution during infiltration: measured and calculated. Soil Sci. Sot. Am. Proc., 39: 820-825.