Influence of phosphorus on the phytotoxicity of alachlor

Abstract

The effects of different levels of phosphorus on the initial and residual activity of alachlor (2-chloro-2, 6-diethyl-N-methoxymethylacetanilide) were studied in glasshouse experiments using German millet (Setaria italica (L.) Beauv.), a species susceptible to alachlor. Results showed that the initial phytotoxicity of alachlor decreased with the increasing rates of phosphorus. As the concentration of the herbicide was increased, higher levels of phosphorus were required to alter its phytotoxicity. The phosphorus concentration in plant tops increased with increments in the phosphorus level of the soil and was unaffected by alachlor at low rates. At high concentrations of the herbicide the phosphorus level of some plant shoots increased significantly, although such increases tended to vary with the size of the shoot. Bioassay data showed no significant influence of phosphorus additions to the soil on the residual activity of alachlor.