Bioactivity, adsorption and persistence of two herbicides in tropical soils

Ismail B. Sahid, K. Kalithasan and A. RahmanA, Department of Botany, Universiti Kebangsaan Malaysia, 43600 UKM, Bangi, Selangor, Malaysia.

A Plant Protection Group, AgResearch, Ruakura Agricultural Research Centre, Hamilton, New Zealand.


The effects of environmental factors on bioactivity, adsorption and persistence of two herbicides, viz. alachlor and terbuthylazine, were studied in the laboratory and greenhouse using cucumber (Cucumis sativus L.) as the bioassay species. The bioactivity of both herbicides was inversely correlated with the organic matter content of the soil and increased with increasing herbicide concentrations. Alachlor adsorption by sand-peat mixture increased proportionately with an increase of soil organic matter content and with increasing herbicide concentration. Half-life of alachlor decreased from 15.2 to 6.2 days as temperature increased from 25 to 35°C in the Selangor Series soil and from 14.5 to 6.2 days in the Serdang Series soil. An increase of temperature from 25 to 35°C also reduced the half-life of terbuthylazine in both soils. The half-life of alachlor decreased at moisture level of 70% field capacity in both soils. However, the dissipation rate of terbuthylazine was significantly faster at 50% field capacity (9.4 days) in Serdang Series than at 70% (11.4 days).


Plant Protection Quarterly (1997) 12 (3) 128-132.