THE IMPACT OF CHLORSULFURON AND DICLOFOP-METHYL ON NUTRIENT-UPTAKE BYWHEAT

The effect of the herbicides chlorsulfuron and diclofop-methyl on nutr ient uptake and utilization by wheat was examined in two glasshouse an d one field experiment. In the glasshouse, chlorsulfuron decreased sho ot weight, root weight and root length. Phosphorus uptake was decrease d by chlorsulfuron, especially when combined with low phosphorus suppl y. Uptake of potassium was also decreased while uptake of nitrogen, ca lcium and magnesium was not affected. Under field conditions, chlorsul furon decreased concentrations of a range of elements in plant shoots during early growth by up to 30%. This effect faded with increasing pl ant age. Chlorsulfuron treatment did not decrease nutrient concentrati ons in mature grain or grain yield. The elements in order of decreasin g sensitivity to chlorsulfuron application were: macro-elements phosph orus, potassium > nitrogen, sulfur > calcium, magnesium and micro-elem ents zinc, copper > manganese > iron. There were differences in sensit ivity to chlorsulfuron treatment between cultivars; Kulin was more sen sitive than Reeves. Diclofop-methyl application had little effect on n utrient 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 her bicides than the uptake of nutrients which principally move by mass fl ow. It is therefore likely that the herbicides are modifying the abili ty of roots to explore soil rather than decreasing absorption at the r oot surface.