New Zealand Journal of Crop and Horticultural Science abstracts

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Pesticide sorption and degradation characteristics in New Zealand soils—a synthesis from seven field trials

Murray E. Close¹
Robert Lee²
Ajit K. Sarmah²
Liping Pang¹
Rod Dann¹
Guna N. Magesan^2,*
Jim P.C. Watt^2,†
Keith W. Vincent^2,‡

¹ Institute of Environmental Science and Research
 P. O. Box 29 181
 Christchurch, New Zealand
 email: murray.close@esr.cri.nz
² Landcare Research NZ Ltd
 Private Bag 3127
 Hamilton, New Zealand
^* Present address: SCION, Private Bag 3020, Rotorua, New Zealand.
^† Present address: 41 Chambers St, Havelock North, New Zealand.
^‡ Present address: Soil Selection Services Limited, P. O. Box 8301, Havelock North, New Zealand.

Abstract The transport and fate of selected pesticides was determined at seven field sites located throughout New Zealand. Mixtures of pesticides and bromide (Br) were applied to plots and soil and water samples, collected at 1–3 monthly intervals over the study period, were analysed for residual pesticides and Br. The maximum depth of sampling varied from 0.92 to 2.5 m for the suction cup samplers and 0.8 to 1.0 m for the soil sampling. Inverse modelling was used with three models, GLEAMS, LEACHM, and HYDRUS, to estimate Koc and half-life values for the applied pesticides. Diazinon and procymidone had much lower Koc values than the selected literature values (SLVs), indicating they will be much more mobile in New Zealand soils than would be expected from the SLVs. Picloram had similar Koc values to the SLV at the Te Awa and Twyford sites but was much less mobile in the allophanic Horotiu soil, as was triclopyr. There was a slight effect of allophane on sorption for hexazinone, picloram, and triclopyr for the Horotiu and Kiripaka soils. Atrazine, simazine, and terbuthylazine Koc values tended to be less than the SLV, whereas bromacil Koc values were greater than the SLV and hexazinone had similar Koc values to the SLV. Diazinon, hexazinone, simazine, and terbuthylazine all had similar half-life values to the SLVs. Atrazine was on average c. 4 times less persistent than the SLV, whereas bromacil was slightly less persistent than the SLV. 2,4-D was about twice as persistent as the SLV would indicate whereas picloram, triclopyr, and procymidone were much more persistent than the SLVs, with factors of 4, 5, and 50, respectively, for these pesticides, and were outside the reported range of literature values. These studies have provided a greater knowledge of field-based Koc and half-life values in New Zealand soils under a range of climatic conditions, and the measured variability in the Koc and half-life values can be used to carry out a sensitivity analysis of leaching predictions.

Keywords 2,4-D; atrazine; bromacil; diazinon; hexazinone; picloram; procymidone; simazine; terbuthylazine; triclopyr; bromide; Koc; half-life; sorption; degradation; inverse modelling

New Zealand Journal of Crop and Horticultural Science, 2008, Vol. 36: 9–30
0014–0671/08/3601–0009      © The Royal Society of New Zealand 2008
H07002; Online publication date 4 March 2008
Received 9 January 2007; accepted 5 December 2007

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