Organic Carbon Soil
Organic Carbon Soil
Effect of pre emergence weedicide on adsorption and desorption in inceptisol soil
Effect of pre emergence weedicide on adsorption and desorption 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 experiment in laboratory at Department of Soil Science and Agricultural Chemistry, Post Graduate Institute, M.P.K.V., Rahuri during 2002-03 to asses the effect of pre emergence weedicide on adsorption and desorption in inceptisol soil. There are four pre emergence weedicide used viz., oxyfluorfen, alachlor, fluchloralin and pendimethalin, in different concentration. The adsorption of pre emergence weedicides were increased with an increased concentration. The mean adsorption of oxyfluorfen, alachlor, fluchloralin and pendimethalin were 9.440, 9.519, 9.560 and 9.652 µg mL-1, respectively. The Freundlich adsorption equation gave good fit for the R2 values. The desorption of pre emergence weedicide was more in fluchloralin (7.740 µg 10 g-1 soil). The per cent desorption were in the order of fluchloralin > alachlor > oxyfluorfen > pendimethalin (17.11 > 14.41 > 13.20 > 12.37per cent), respectively. (Key Words – Adsorption, desorption, Pre emergence weedicides, Freundlich adsorption isotherm)
The tendency of pesticides to be adsorbed by soil is determined largely by the characteristics of pesticides and soils. The adsorption is directly associated with the soil characteristics like organic matter, nature and amount of clay and sesquioxides contents. Once a weedicide finds its way into the environment, a major part of it comes in contact with soil. Adsorption influences almost all the reactions of pesticides in soil. The adsorbed compound persists in soil for a longer time. This phenomenon therefore, appear to be one of the major factors affecting weedicide soil interactions. The adsorption, desorption and interaction of weedicides are the most significant processes influencing persistence, movement and efficacy of weedicide in soils. These phenomenon lead to physico-chemical charges, including nutrient availability and susptibility to microbial degradation in soils.
Material and Methods –
Adsorption of pre emergence weedicides
Concentration of weedicides viz., pendimethalin, alachlor, fluchloralin and Oxyfluorfen were used for adsorption study was 1 mg, 5 mg, 3. 10 mg,15 mg, 20 mg and 25 mg a.i. kg-1 Soil. For this the procedure was used as ten gram soil was shaken with 20 ml solution of pre emergence weedicide separately in plastic tubes on horizontal shaker for four hours. The working solution having 1, 5, 10 and 25 mg g-1 acetone solution concentration were prepared separately. To ten gram soil, 20 ml each of working solution were added to give concentration 1, 5, 10 and 25 mg g-1 soil. After four hours equilibration at room temperature the tubes were centrifuged for 5 minutes at 1000 rpm. Ten milliliter of aliquot was taken for pre emergence weedicide content.
Pre emergence weedicide were estimated by gas chromatography method described in pesticide Analytical Manual Vol. II. The pre emergence weedicide adsorbed were calculated by difference in concentration of this herbicide originally present in equilibrating solution and that after equilibration. Per cent adsorbed of these weedicide were calculated.
Desorption studies of pre emergence weedicides
To determine pre emergence weedicide desorption characteristics of soil, the method suggested by Wahid and Sethunathan (1978) was followed. Soil samples equilibrated with 20 ml of 5 mg g-1 pre emergence weedicide were centrifuged and 10 ml aliquot were taken out separately for analysis. The samples were resuspended with the help of shaker and equilibrated for 2 hrs. Distilled water washing was analysed separately for pre emergence weedicide. The total and per cent pre emergence were calculated.
Adsorption isotherm
The adsorption isotherm was obtained by plotting data of pendimethalin, alachlor fluchloralin and Oxyfluorfen adsorbed against equilibrating concentrations.
The isotherm data were interpreted interms of Freundlich equation.
X
——— = KC1/n
m
where,
X/m = Amount of weedicide (X) adsorbed per gram of soil
C = Weedicide concentration in equilibrium solution
K = Constant
In practical terms a straight line is obtained when data were plotted as log (X/m) Vs. log C. The intercept is equal to log K and slope to 1/n.
The constant K provides indication of the extent of adsorption and has sometimes been used in correlation studies for determining the relative importance of the various soil properties on adsorption.
Theoretically, Freundlich equation represents a situation in which the quantity of weedicide adsorbed increases indefinitely with increasing concentration. This was occur when multilayer are formed and also heterogeneous sorption sites are implied.
Results and Discussion
Adsorption of weedicide in inceptisol soil
The adsorption of pre emergence weedicide as influenced by weedicide concentration in equilibrating solution are reported in Table 1. The adsorption of pre emergence weedicide were varied considerably by the equilibrium concentration in solution. The adsorption of pre emergence weedicide did not varied by the type of weedicide. The adsorption of pre emergence weedicide was increased with an increased concentration in equilibrating solution irrespective of pre emergence weedicide. It was 0.780, 4.572, 9.672 and 23.272 µg mL-1 in 1, 5, 10 and 25 µg mL-1 concentration of pre emergence weedicides, respectively. The adsorption of pre emergence weedicide irrespective of concentration of equilibrating solution was numerically more in pendimethalin (9.652 µg mL-1) followed by fluchloralin (9.560 µg mL-1) and alachlor (9.519 µg mL-1). It was the least in oxyfluorfen (9.440 µg mL-1). The variation in adsorption phenomenon of pre emergence weedicide might be associated with the adsorption of pre emergence weedicide mainly depends on nature of weedicide, soil organic matter, soil reactions and type and clay content. Similarly mobility, solubility and polarity of the weedicides. Primarily the adsorption of weedicide occurred on humic substances. It was decided by polarity power of exchangeable cations and hydrogen bonding between C=O. Functional groups, carboxyl oxygen and amide nitrogen was assumed to contribute to bond formation between clay and herbicide (Weiping et al. 2000). The interaction between phenyl ring of weedicide and organic carbon (Nir et al. 2000).The higher adsorption of pendimethalin on soil might be because of their higher mobility.
Freundlich adsorption
The data obtained were used for fitting in Freundlich equation. The equation thus obtained and goodness of fit of data are given by coefficient of determination (R2) which are reported in Table 4. The R2 values of Freundlich equations were 1, 1, 1, and 1 for oxyfluorfen, alachlor, fluchloralin and pendimethalin indicated good fit of equation.
Quantity (K) and Intensity factor (1/n) - The data on Freundlich adsorption constant i.e. quantity (K) and intensity factor (1/n) calculated by regression equation of Freundlich adsorption isotherm are reported in Table 5. The K values which are the measure of the capacity factor were almost in order of combine adsorption capacities of pre emergence weedicide. The intensity factor measured by 1/n does not vary greatly in pre emergence weedicide oxyflurofen (0.83) and alachlor (0.84). Similarly, in fluchloralin (0.90) and pendimethalin (0.90). The difference in quantity and intensity factor of pre emergence weedicides are might be due to soil system composed of silicate and organic matter which is highly heterogeneous and hence constant loosing their inherent meaning.
Desorption of pre emergence weedicide
The per cent desorption of pre emergence weedicide are presented in Table 6. The initial values of adsorbed weedicide were numerically higher in pendimethalin (48.95 mg 10 g-1 soil) followed by fluchloralin, alachlor and oxyfluorfen (45.25, 44.90 and 42.75 mg 10 g-1 soil respectively). The desorption of weedicide at Ist, IInd and IIIrd washing revealed that the desorption were decreased with increased washings. The total desorption of weedicides was the least in oxyfluorfen (5.646 mg 10 g-1 soil) followed by pendimethalin (6.658 mg 10 g-1 soil). The highest desorption was observed in fluchloralin (7.740 mg 10 g-1 soil) followed by alachlor (6.470 mg 10 g-1 soil). The per cent desorption of pre emergence weedicide were in the order of fluchloralin > alachlor > oxyfluorfen > pendimethalin (17.11 > 14.41 > 13.20 > 12.37 per cent respectively). These observations are conformity with Raj et al. (1999). The desorption studies of pre-emergence weedicide revealed that fluchloralin and alachlor weedicides were more beneficial than the pendimethalin and oxyfluorfen.
Conclusions
The adsorption of pendimethalin and fluchloralin were higher
than alachlor and oxyfluorfen. The higher concentration equilibrium solution observed in Oxyfluorfen and alachlor. The Freundlich adsorption equation gave good fit for the R2 values. The desorption of fluchloralin was higher than the other pre emergence weedicide.
References –
*Nir, S., Undabeytia, T., yaron Marcovich, D., El-Nahhal, Y., Polubesova, T., Serban, C., Rytwo, C., Lagaly, C. and Rubin, B. 2000. Optimization of adsorption of hydrophobic herbicides on montmorillionite pre adsorbed by monovalent organic cations, interaction between phenyl ring. Envion. Sci. Techn. 34 (7) : 1269-1274.
*Raj, M.F., Patel, B.K. and Shah, P.C. 1999. Adsorption, desorption of pendimethalin, fluchloralin and oxadiazon on soils. Pesti. Res. J. 11 (2) : 162-167.
Wahid, P.A. and Sethunathan, N. 1978. Sorption desorption of herbicide in soils. J. Agric. Fd. Chem. 26(1) : 101-105
Weiping Liu, Jianying Gan, Sharon, K., Papiernik and Scott, R. Yates. 2000. Structural influences in relative sorptivity of chloroacetanilide herbicides in soils. J. Agric. Fd. Chem. 48 : 4320-4325.
* Originals are not seen.
Table 1. Adsorption of weedicide in Inceptisol Soil
Sr. No.
Different weedicide
Weedicide adsorbed (µg g-1)
Weedicide Concentration in equilibrating solution (µg ml-1)
1
5
10
25
Mean
1
Oxyfluorfen
0.745
4.400
9.505
23.110
9.440
2
Alachlor
0.754
4.490
9.645
23.185
9.519
3
Fluchloralin
0.785
4.525
9.710
23.220
9.560
4
Pendimethalin
0.838
4.895
9.830
23.574
9.652
Mean
0.780
4.572
9.672
23.272
Table 2. Coefficient of determination (R2) indicating goodness of fit to freundlich equation
Sr. No.
Weedicide
R2
Freundlich Equation
1
Oxyfluorfen
1
X/m=0.62 C0.83
2
Alachlor
1
X/m=0.60 C0.84
3
Fluchloralin
1
X/m=0.67 C0.90
4
Pendimethalin
1
X/m=0.68 C0.90
Table 3. Freundlich adsorbtion constant of weedicide in inceptisol soil
Sr.
No.
Different weedicide
Freundlich adsorption constant
K
1/n
1
Oxyfluorfen
0.62
0.83
2
Alachlor
0.60
0.84
3
Fluchloralin
0.67
0.90
4
Pendimethalin
0.68
0.90
Table 4. Desorption of different weedicide in soil
Sr.
No.
Different weedicide
Weedicide adsorbed (µg 10 g-1 soil)
Weedicide desorbed (µg 10 g-1)
Per cent desorpt-ion
Washing I
Washing II
Washing III
Total
1
Oxyfluorfen
42.75
3.521
1.287
0.838
5.646
13.21
2
Alachlor
44.90
3.982
1.595
0.893
6.470
14.41
3
Fluchloralin
45.25
4.22
2.602
0.925
7.740
17.11
4
Pendimethalin
48.95
3.641
1.435
0.982
6.058
12.37
How soil organic matter and soil organic carbon relatd conceptually and quantitatively?
Why is the term organic carbon more appropriate for quantitative scientific discussion?
Soil organic matter is the fraction of soil exclusive of the undecayed or undecomposed plant and animal residues- synonymous with humus (non-mineral component). You will hear the term organic matter % being used in agriculture and in soil erosion literatures.
Soil Organic carbon is a component of the Soil organic matter. Organic carbon is composed of a variety of compounds in different oxidation states. Total organic carbon refers to the organic and inorganic portions of the carbon.
Inorganic Carbon-carbonates, bicarbonates, and dissolved CO2
Organic Carbon- all organic portions
Inorganic carbon can be eliminated by acidifying samples to a pH less than 2.
Organic carbon is used in scientific discussions because it has much importance in drinking water quality, nutrient cycling, ion exchange capacity, and nutrient sources for microbes.
Hope it helps
Soil and Water scientist.
A Ackhurst RIFT soil carbon
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