Plant sensitivity to atrazine and chlorsulfuron residues in a soil-free system

The sensitivity of 22 major crops, pastures and weeds from the north-east g rain region of Australia to atrazine and chlorsulfuron residues was determi ned in a glasshouse using a soil-free bioassay system. A logistic equation was fitted to the seedling fresh weights as a function of the logarithm of herbicide concentration by non-linear regression and used to calculate the doses for 10%, 30% and 50% inhibition of seedling growth (ID10, ID30 and ID 50) The ID50 for atrazine ranged from 0.03 to 0.04 mg a.i, L-1 for Salvia r eflexa Hornem. and barley to 1.47 mg a.i. L-l for sorghum, The ID50 for chl orsulfuron ranged from 0.19 to 0.21 mu g a.i. L-1 for lucerne and snail med ic to 102 mu g a.i. L-1 for wheat. Based on ID50 values measured, the predi cted responses of each species to a range of concentrations of atrazine and chlorsulfuron were classified into four categories ranging from no damage to severe damage. These sensitivity data will assist in planning cropping s equences in soils previously treated with atrazine or chlorsulfuron.