View Full Table | Close Full ViewTable 1.

Selected soil characteristics of the Lanna clay and the Nåntuna sand. Standard laboratory methods were used throughout (Bergström et al., 1994).

 
Layer Soil texture (Gr/Sa/Si/Cl)† Organic matter Cation exchange capacity Bulk density pH‡ Water content at tensions (cm)
100 15,000
cm % cmolc kg−1 g cm−3 m3 m−3
Clay
0–30 1.3/6.0/46.2/46.5 4.4 28.4 1.24 7.2 0.524 0.359 0.193
30–60 0.6/2.7/40.6/56.1 0 33.6 1.43 7.4 0.477 0.249
60–90 0.2/1.8/37.4/60.6 0 1.46 7.4 0.468 0.297
Sand
0–30 0/87.8/4.5/7.7 2.0 4.7 1.43 7.4 0.448 0.180 0.034
30–60 0/95.4/4.6/0 1.0 1.8 1.47 6.4 0.427 0.165 0.019
60–90 1.0 1.4 1.46 7.0 0.450 0.065 0.016
Gr = gravel, >2 mm; Sa = sand, 0.06–2 mm; Si = silt, 0.002–0.06 mm; Cl = clay, <0.002 mm.
Determined in water.
§ Equivalent to porosity.



View Full Table | Close Full ViewTable 2.

Molecular weights, retention times (RT) and specific selected ions for compound derivatives.

 
Molecule Molecular weight RT (min) Quantification ion (m/z, % relative abundance) Qualification ion (m/z, % relative abundance)
AMPA† 371 4.49 126 (100) 302 (23)
AMPA‡ 375 4.49 130 (100) 306 (22)
Glyphosate 511 5.35 411 (100) 384 (50)
Glyphosate‡ 513 5.35 413 (100) 386 (48)
AMPA = aminomethylphosphonic acid.
Internal standard.



View Full Table | Close Full ViewTable 3.

Freundlich coefficients (K f) (± SE, n = 10) for adsorption of glyphosate obtained by nonlinear regression according to Eq. [1]

 
Soil K f 1/n R 2
μg1-n (mL) n g−1
Sand topsoil 40.0 ± 2.9 0.92 ± 0.04 0.997
Sand subsoil 28.7 ± 1.2 0.82 ± 0.02 0.998
Clay topsoil 118 ± 4.4 0.95 ± 0.01 1.000
Clay subsoil 165 ± 10.7 1.03 ± 0.02 0.999



View Full Table | Close Full ViewTable 4.

Coefficients (± SE, n = 12) obtained by nonlinear regression for degradation of glyphosate according to first-order kinetics (Eq. [2]).

 
Soil c G0 k R 2 t 1/2 DT90 §
mg kg−1 d−1 d d
Sand topsoil 11.21 ± 0.33 0.041 ± 0.003 0.978 16.9 56.2
Sand subsoil 12.27 ± 0.19 0.019 ± 0.001 0.985 36.5 121
Clay topsoil 11.99 ± 0.15 0.0063 ± 0.0005 0.948 110 365
Clay subsoil 11.61 ± 0.41 0.0046 ± 0.0014 0.562 151 501
c G0 = initial concentration of glyphosate; k = first-order rate coefficient for degradation; t1/2, = half-life; DT90 = time for 90% degradation.
Calculated as ln(2)/k.
§ Calculated as ln(10)/k



View Full Table | Close Full ViewTable 5.

Coefficients (± SE, n = 12) obtained by nonlinear regression for formation and degradation of aminomethylphosphonic acid (AMPA) according to Eq. [4]

 
Soil k 1 k 2 t 1/2 R 2
d−1 d
Sand topsoil 0.0216 ± 0.0011 0.0115 ± 0.0019 60.4 0.965
Sand subsoil 0.0092 ± 0.0005 0.0076 ± 0.0018 91.3 0.988
Clay topsoil 0.0063§ ± 0.0005 0.0199 ± 0.0013 34.9 0.973
Clay subsoil 0.0028 ± 0.0006 0.0071 ± 0.0087 97.6 0.901
k 1 = first-order rate coefficient for degradation of glyphosate to AMPA; k 2 = first-order rate coefficient for degradation of AMPA ; t 1/2 = half-life.
Calculated as ln(2)/k 2
§ In the clay topsoil, k 1 became 0.0073, i.e., larger than k (first-order rate coefficient for degradation; Table 4), leading to a formation fraction > 1, and was therefore set equal to k



View Full Table | Close Full ViewTable 6.

Derived parameter values on fraction of glyphosate degraded to aminomethylphosphonic acid (AMPA) (k 1/k), rate constant for formation of sarcosine (k 3), incubation time (t Amax) at which the AMPA-concentration peaks (c Amax), and c Amax as fraction of initially added glyphosate.

 
Soil k 1/k k 3 t Amax § c Amax c Amax fraction#
d−1 d mg kg−1 %
Sand topsoil 0.53 0.0190 43.4 2.40 32.4
Sand subsoil 0.48 0.0098 80.4 2.12 26.2
Clay topsoil 1 0 84.7 1.47 18.6
Clay subsoil 0.61 0.0018 174 1.34 17.5
Values of k (first-order rate coefficient for glyphosate degradation) from Eq. [2] (Table 4) and of k 1 (first-order rate coefficient for degradation of glyphosate to AMPA) from Eq. [4] (Table 5).
k 3 = kk 1
§ Calculated according to Eq. [5]
Obtained by inserting derived values of k, k 1, k 2, c G0, and t Amax into Eq. [4]
# Calculated as (c Amax × 1.52 × 100)/c G0, where 1.52 is the stoichiometric factor for conversion of AMPA to glyphosate concentration.



View Full Table | Close Full ViewTable 7.

Water inputs to the lysimeters and mean annual amounts of leachate from the lysimeters to which glyphosate was applied (± SD; n = 2 for sand, n = 3 for clay)

 
Year No. of days Precipitation + irrigation Leachate
Sand lysimeters Clay lysimeters
mm
2006† 104 232 169 (± 1.4) 156 (± 4.7)
2007 365 550 229 (± 3.2) 158 (± 9.1)
2008‡ 261 432§ 174 (± 13) 148 (± 4.0)
Total 730 1214 572 (± 17) 461 (± 15)
Measurements made during the period 18 September to 31 December.
Measurements made during the period 1 January to 18 September.
§ Includes 22 mm irrigation.