title: Effect of rainfall regimes and mulch decomposition on the dissipation and leaching of S-metolachlor and glyphosate: a soil column experiment.
abstract: BACKGROUND
  Interception by plant residues is a major process affecting pesticide persistence and leaching in conservation agriculture. Dissipation and leaching of S-metolachlor and glyphosate was studied in repacked soil columns covered with a mulch of maize and lablab residues. The columns were submitted to two contrasting simulated rainfall regimes: one with light but frequent rain (LF) and one with less frequent but more intense rain (HI). In both treatments, columns received the same amount of rainwater by the end of the experiment.
  
  
  RESULTS
  Decomposing crop residues on the soil surface retained more than 50% of the applied amount of pesticide. S-metolachlor dissipation in mulch residues was faster under the LF rainfall regime. This was attributed to more humid surface conditions, under which mulch decomposition was also faster. The formation of metabolites of both molecules was higher under the LF rainfall regime. However, leaching of S-metolachlor and its metabolites to deeper soil layers was greater under the HI rainfall regime, whereas they accumulated in the surface layer under the LF rainfall regime. Glyphosate remained in the surface soil layer because of its strong adsorption capacity, whereas aminomethylphosphonic acid leached down in small amounts without any difference between the two rainfall regimes.
  
  
  CONCLUSIONS
  The impact of mulch residues on herbicide dissipation was strongly dependent on molecule type and rainfall regime. © 2014 Society of Chemical Industry.
authors.affiliation: INRA, UMR 1091 EGC, 78850 Thiverval-Grignon, France; Forman Christian College, Lahore 54600, Pakistan.
authors.forename: Sohaib
authors.initials: S
authors.lastname: Aslam
authors.forename: Akhtar
authors.initials: A
authors.lastname: Iqbal
authors.forename: Marjolaine
authors.initials: M
authors.lastname: Deschamps
authors.forename: Sylvie
authors.initials: S
authors.lastname: Recous
authors.forename: Patricia
authors.initials: P
authors.lastname: Garnier
authors.forename: Pierre
authors.initials: P
authors.lastname: Benoit
mesh_terms: D000081:Acetamides / Q000737:chemistry*; D002980:Climate; D005998:Glycine / Q000031:analogs & derivatives* / Q000737:chemistry; D006540:Herbicides / Q000737:chemistry*; D011891:Rain; D012987:Soil / Q000737:chemistry*; D012989:Soil Pollutants / Q000737:chemistry*; D000097797:Glyphosate
chemical_list: D000081:Acetamides; D005998:Glycine; D006540:Herbicides; D012987:Soil; D012989:Soil Pollutants; D000097797:Glyphosate; C051786:metolachlor
keywords: degradation; mulch; pesticide wash-off; rainfall regimes; soil columns