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August 25th, 2010 | 
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Effect of pre emergence weedicide on soil metabolic activity in inceptisol soil
Effect of pre emergence weedicide on soil metabolic activity
in laboratory under ambient condition in inceptisol soil.
Megha V. Nagmote and A. D. Kadlag
Department of Soil Science and Agriculture Chemistry
Mahatma Phule Krishi Vidyapeeth, Rahuri-413722,
Dist. Ahmednagar, Maharashtra.
-----------------------------------------------------------------------------------Abstract : The present investigation was carried out by conducting an incubation study. The incubation study was carried out in laboratory under ambient condition at Department of Soil Science and Agricultural Chemistry, Post Graduate Institute, M.P.K.V., Rahuri during 2002-03 to asses the periodical soil microbial population and enzyme activities viz., urease, acid phosphatase and dehydrogenase. The application of alachlor @ 1.0, 2.0 and 4.0 kg a.I. ha-1 were recorded the higher urease activity at 21st days (20.97, 20.83 and 20.85 mg NH4-N 100 g-1 soil hr-1 respectively) The acid phosphatase activity in laboratory incubation were increased at 21st days by alachlor @ 1.0, 2.0 and 4.0 kg a.i. ha-1 (9.532, 9.985 and 9.761 µMP g-1 soil hr-1, respectively). The soil dehydrogenase activity was higher at 21st days of incubation by the pre emergence weedicides.
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Soil is a storehouse of plant nutrients for the growth and development of crop plants. The fertility of soil is governed by the enzymes that may be exoenzymes (free enzymes) or endoenzymes released from disintegration of cells. Nutrient cycling in soil involves biochemical and physiochemical reactions with the biochemical processes being mediated by microorganisms, plant roots and soil animals. All biochemical reactions are catalysed by enzymes. The microbes are small but their role in improving agricultural productivity and soil health is profound. Looking at the huge workforce of invisible tiny microbes, working wonders, doing thankless jobs silently for human welfare, one cannot but appreciate ‘Yes, the small is always beautiful (Anonymous, 2000).
Materials and Methods
The incubation study was carried out in laboratory under ambient condition at Department of Soil Science and Agricultural Chemistry, Post Graduate Institute, M.P.K.V., Rahuri during 2002-03 to asses the periodical soil microbial population and enzyme activities viz., urease, acid phosphatase and dehydrogenase. There are fourteen treatment comprised of pre emergence weedicide application viz., oxyfluorfen, alachlor, fluchloralin and pendimethalin in graded dose, weedy check and weed control. The soil of used for laboratory study is grouped under Inceptisol soil order belonging to Sawargaon (Pather) soil series.
Soil enzyme assay
Urease enzyme assay (Urea amidohydrolase, EC 3.5.1.5)
The urease enzyme assay was carried out according to the method described by Tabatabai and Bremner (1972).
Reagents used Tris (hydroxymethyl) amino methane (THAM) buffer, 0.05 M, pH 9.0 ,Urea solution - 0.2 M, Potassium chloride – 2.5 M – Silver sulphate (100 ppm) (KCl – Ag2SO4) solution, Sodium hydroxide - 2.5 %, Boric acid - 2 %, Mixed indicator, Working boric acid solution, H2SO4 - 0.1 N (Stock Solution)
Method - Five gram of soil was taken in 50 ml of clean dry conical flask. In each conical flask 0.2 ml of toluene and 9 ml of THAM buffer were added. The conical flask was incubated in water both for 30 minutes at 370c temperature. The conical flasks were replaced from the water bath and approximately 35 ml of potassium chloride silver sulphate solution (KCl – Ag2SO4) was added. The content was shaken for few seconds and diluted to 50 ml volumetric flasks and were inverted several times and allowed to settle. Twenty milliliters of supernatant liquid was used for ammonical nitrogen (NH4-N) estimation by micro-kjeldahl method.
Acid phosphatase enzymeassay(Orthophosphoric monoester phosphohydrolase, EC 3.1.3.2) - For the assay of acid phosphatase enzyme, extraction was done by the method of Tabatabai and Bremner (1969). Reagents - Modified universal buffer (MUB) stock solution, Modified Universal Buffer (MUB), pH 6.5, Na - b - Glycerophosphate - 0.1 M, Ammonium molybdate - 5 %, Perchloric acid - 60 %, Aminonapthol sulphonic acid (ANSA), Standard phosphorus solution - 0.01 M.
Method - Acid phosphatase enzyme was extracted from soil by the procedure of Tabatabai and Bremner (1969). Five gram of soil was taken in 50 ml conical flask. In each conical flask 1 ml toluene, 20 ml modified universal buffer (MUB pH 6.5) and 5 ml of Na-b-glycerophosphate were added. The flask were replaced from water bath and kept in boiling water bath for 15 minutes to kill the enzyme activity. The content was filtered and 5 ml of extract was used for colour development. For colour development the procedure given by King (1932) was used. Five ml of filtrate was pipetted out in clean dry 25 ml volumetric flaks to which 1 ml of ammonium molybdate, 1.2 ml of perchloric acid and 1 ml of ANSA were added and final volume was made to 25 ml with distilled water for colour development. The absorbance was read on Spectronic-20 at 663 nm after 30 minutes against blank. The amount of inorganic phosphorus produced was calculated from the standard curve and the acid phosphatase activity was expressed in terms of mM ‘P’ g-1 soil hr-1.
Calibration of standard curve - In a series of 25 ml volumetric flask 0, 0.1, 0.2, 0.3 ….. 1 ml of 0.01 M phosphorus solution were pipetted out in triplicates. Rest of the procedure was same as described in the colour development. The standard curve was plotted on a graph paper taking mM of phosphorus concentration value against the absorbance at 663 nm.
Dehydrogenase enzyme assay - The dehydrogenase enzyme activity assay was carried out by the method described by Casida et al. (1964).
Procedure - Taken 6 screwed capped test tube of 15 ml capacity, one gram finely powdered soil in each of the tube were added, then added 500 mg FYM in each tube, one ml of 3 % TTC and 0.5 ml of 1 % glucose in each tubes were imposed, taped the tubes so that no air bubble remain in soil. A thin layer of water should form above the soil.Incubated for 12 hrs.Added 10 ml of methanol. Vigorously shaked the flasks and allowed to stand in dark for 24 hrs. Withdraw supernant and measure colour intensity using blue filter at 480 nm on Spectronic-20. The absorbance was proportional to the concentration of TPF formed.
Result and Discussion –
The periodical soil urease enzyme activity as influenced by the pre emergence weedicides in incubation study are presented in (Table 1). The urease enzyme activity was numerically increased up to 21 days of incubation over 7 and 14 days of incubation in all the weedicide application. The maximum urease enzyme activity was recorded in alachlor pre emergence weedicide application @ 1.0, 2.0 and 4.0 kg a.i. ha-1 (20.97, 20.83 and 20.65 mg NH4-N 100 g-1 soil hr-1 respectively) followed by fluchloralin @ 0.75, 1.50 and 3.0 kg a.i. ha-1 (19.88, 19.65 and 18.93 mg NH4-N 100 g-1 soil hr-1 respectively). The urease enzyme activity at 45 and 60 days of incubation were drastically reduced in all the pre emergence weedicide application. The reduction in urease enzyme activity might be related with the decreased soil microbial population and enzyme concentration in soil. This observation is corroborated with the Ramesh et al. (2000)
The soil acid phosphatase enzyme activity as influenced by the levels of different pre emergence weedicides under laboratory conditions are presented in (Table 2). The highest soil acid phosphatase activity at 21 days of incubation was observed in pre emergence application of alachlor @ 1.0, 2.0 and 4.0 kg a.i. ha-1 (9.532, 9.985 and 9.761 mM P g-1 soil hr-1 respectively) followed by fluchloralin application @ 0.75, 1.50 and 3.00 kg a.i. ha-1 (9.341, 8.829 and 8.934 mM P g-1 soil hr-1 respectively). These observations revealed that use of alachlor as pre emergence weedicide is more beneficial for soil acid phosphatase activity followed by fluchloralin. This might be ascertained that these weedicides did not inhibit the microbial population in soil which in turn resulted in higher soil acid phosphatase activity. These results are in accordance with Pozo et al. (1994) and Nagaraja et al. (1998).
The soil dehydrogenase activity as influenced by the application of pre emergence weedicide are depicted in (Table 3). It was maximum in lower dose of alachlor @ 1.0 kg a.i. ha-1 fluchloralin and pendimethalin @ 0.75 kg a.i. ha-1 (0.384, 0.451 and 0.497 m mol formazon g-1 soil day-1 respectively). The variation in soil dehydrogenase activity might be because of microbial population and their activity in soil. The 21 days of incubation showed the higher soil dehydrogenase activity by application of alachlor @ 1.0, 2.0 and 4.0 kg a.i. ha-1 (0.631, 0.653 and 0.697 m mol g-1 soil day-1 respectively). The fluchloralin weedicide also showed the higher soil dehydrogenase activity at 45 days (0.475, 0.485 and 0.359 m mol g-1 soil day-1 respectively) and 60 days of incubation (0.346, 0.374 and 0.364 m mol g-1 soil day-1 respectively).
Conclusions - The application of alachlor pre emergence weedicide recorded the maximum urease activity at 21st days of an incubation followed by fluchloralin. The highest acid phosphatase activity was recorded at 21st days of an incubation by alachlor as pre emergence weedicide. The maximum dehydrogenase activity was observed at 21st days of incubation by the pre emergence weedicide.
References –
Anonymous. 2000. Microbes for sustainable agriculture Indian Fmg. pp. 39-41.
Casida, L.E., Klein, D.A. and Santro, T. 1964. Soil dehydrogenase activity. Soil Sci. 98 : 371-376.
Nagaraja, N.S., Ramakrishna Parama, V.R. and Siddaramappa, R. 1998. Effect of attrazine on urea N. mineralization and activity of some soil enzymes. J. Indian Soc. Soil Sci. 46(2) : 182-192.
Pozo, L., Salmeron, V., Rodelas, B., Martinez-Toleds, M.V. and Gonzatez-Lopez, J. 1994. Effect of herbicide alachlor on soil microbial activities. Ecotoxicol. 3(1) : 4-10.
Ramesh, A., Joshi, O.P. and Billore, S.D. 2000. Effect of herbicides on soil dehydrogenase and urease activity in soybean. Indian J. agric. Sci. 70(4) : 218-219.
Tabatabai, M.A. and Bremner, J.M. 1969. Use of nitrophenyl phosphate for assay of soil phosphatase activity. Soil Biol. Biochem. 1 : 301-307.
Table 1. Effect of pre emergence weedicide on perodical urease enzyme activity in inceptisol soil under laboratory condition
Sr. No.
Treatment
Urease enzyme activity
(mg NH4-N 100 g-1 soil hr-1)
7 days
14 days
21 days
45 days
60 days
1.
Oxyfluorfen
0.5 kg a.i. ha-1
15.58
16.65
18.68
11.98
11.84
2.
Oxyfluorfen
1.0 kg a.i. ha-1
14.61
15.84
18.32
11.83
11.57
3.
Oxyfluorfen
2.0 kg a.i. ha-1
14.32
14.68
17.90
11.58
10.92
4.
Alachlor
1.0 kg a.i. ha-1
17.95
17.98
20.97
15.65
14.79
5.
Alachlor
2.0 kg a.i. ha-1
17.88
17.93
20.83
14.93
14.55
6.
Alachlor
4.0 kg a.i. ha-1
16.98
17.78
20.65
14.73
14.17
7.
Fluchloralin 0.75 kg a.i. ha-1
16.96
16.96
19.88
13.87
13.68
8.
Fluchloralin 1.50 kg a.i. ha-1
16.72
16.88
19.65
13.53
12.83
9.
Fluchloralin
3.0 kg a.i. ha-1
15.47
16.65
18.93
13.28
12.75
10.
Pendimethalin 0.75 kg a.i. ha-1
16.98
16.89
19.81
13.85
13.92
11.
Pendimethalin 1.50 kg a.i. ha-1
16.87
16.77
19.45
13.69
13.69
12.
Pendimethalin 3.0 kg a.i.ha-1
15.25
15.93
18.89
12.85
13.55
13.
Weedy check
13.99
14.32
16.69
15.22
16.30
14.
Control
14.03
14.48
17.27
16.37
16.63
( Initial urease enzyme activity – 13.98 mg NH4-N 100 g-1 soil hr-1)
Table 2. Effect of pre emergence weedicide on perodical acid phosphatase enzyme activity in inceptisol soil under laboratory condition
Sr. No.
Treatment
Acid phosphatase enzyme activity
(µM P g-1 soil hr-1)
7 days
14 days
21 days
45 days
60 days
1.
Oxyfluorfen
0.5 kg a.i. ha-1
3.753
6.345
7.952
5.689
4.657
2.
Oxyfluorfen
1.0 kg a.i. ha-1
2.922
5.861
7.637
5.851
4.491
3.
Oxyfluorfen
2.0 kg a.i. ha-1
2.848
5.980
7.485
5.948
4.648
4.
Alachlor
1.0 kg a.i. ha-1
4.942
7.831
9.532
6.985
5.899
5.
Alachlor
2.0 kg a.i. ha-1
4.893
7.989
9.985
6.743
5.736
6.
Alachlor
4.0 kg a.i. ha-1
4.628
7.574
9.761
6.538
5.758
7.
Fluchloralin 0.75 kg a.i. ha-1
4.782
7.953
9.341
6.854
5.635
8.
Fluchloralin 1.50 kg a.i. ha-1
3.831
6.795
8.829
6.481
5.813
9.
Fluchloralin
3.0 kg a.i. ha-1
3.788
6.647
8.934
5.973
5.987
10.
Pendimethalin 0.75 kg a.i. ha-1
3.831
6.893
8.685
6.343
5.435
11.
Pendimethalin 1.50 kg a.i. ha-1
3.688
6.576
8.742
5.718
4.988
12.
Pendimethalin 3.0 kg a.i.ha-1
3.423
6.487
8.533
5.895
4.713
13.
Weedy check
2.632
5.742
6.861
5.431
4.328
14.
Control
2.471
5.396
6.438
5.287
3.986
(Initial phosphatase enzyme activity – 2.392 µM P g-1soil hr-1)
Table 3. Effect of pre emergence weedicide on perodical acid dehydrogenase enzyme activity in inceptisol soil under laboratory condition
Sr. No.
Treatment
Soil dehydrogenase enzyme activity
(µmol formazon g-1 soil day-1)
7 days
14 days
21 days
45 days
60 days
1.
Oxyfluorfen
0.5 kg a.i. ha-1
0.292
0.438
0.477
0.375
0.267
2.
Oxyfluorfen
1.0 kg a.i. ha-1
0.361
0.489
0.468
0.343
0.257
3.
Oxyfluorfen
2.0 kg a.i. ha-1
0.288
0.476
0.484
0.324
0.219
4.
Alachlor
1.0 kg a.i. ha-1
0.384
0.587
0.631
0.384
0.285
5.
Alachlor
2.0 kg a.i. ha-1
0.373
0.595
0.653
0.393
0.274
6.
Alachlor
4.0 kg a.i. ha-1
0.352
0.583
0.697
0.358
0.224
7.
Fluchloralin 0.75 kg a.i. ha-1
0.451
0.432
0.584
0.475
0.346
8.
Fluchloralin 1.50 kg a.i. ha-1
0.487
0.484
0.578
0.485
0.374
9.
Fluchloralin
3.0 kg a.i. ha-1
0.342
0.573
0.530
0.359
0.361
10.
Pendimethalin 0.75 kg a.i. ha-1
0.497
0.481
0.655
0.447
0.291
11.
Pendimethalin 1.50 kg a.i. ha-1
0.343
0.597
0.587
0.452
0.337
12.
Pendimethalin 3.0 kg a.i.ha-1
0.381
0.442
0.688
0.466
0.245
13.
Weedy check
0.245
0.332
0.442
0.316
0.259
14.
Control
0.203
0.248
0.327
0.283
0.134
(Initial dehydrogenase enzyme activity – 0.269 µmol formazon g-1 soil day-1)
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