THE IMPACT OF CHLORSULFURON AND DICLOFOP-METHYL ON NUTRIENT-UPTAKE BY WHEAT

The effect of the herbicides chlorsulfuron and diclofop-methyl on nutrient uptake and utilization by wheat was examined in two glasshouse and one field experiment. In the glasshouse, chlorsulfuron decreased shoot weight, root weight and root length. Phosphorus uptake was decreased by chlorsulfuron, especially when combined with low phosphorus supply. Uptake of potassium was also decreased while uptake of nitrogen, calcium and magnesium was not affected. Under field conditions, chlorsulfuron decreased concentrations of a range of elements in plant shoots during early growth by up to 30%. This effect faded with increasing plant age. Chlorsulfuron treatment did not decrease nutrient concentrations in mature grain or grain yield. The elements in order of decreasing sensitivity to chlorsulfuron application were: macro-elements phosphorus, potassium > nitrogen, sulfur > calcium, magnesium and micro-elements zinc, copper > manganese > iron. There were differences in sensitivity to chlorsulfuron treatment between cultivars; Kulin was more sensitive than Reeves. Diclofop-methyl application had little effect on nutrient concentration in plant shoots. Zinc and copper concentrations were reduced in vegetative growth, although only copper concentrations were reduced in mature grain of Kulin. The uptake of nutrients which principally move to plant roots by diffusion was decreased more by herbicides than the uptake of nutrients which principally move by mass flow. It is therefore likely that the herbicides are modifying the ability of roots to explore soil rather than decreasing absorption at the root surface.