Effect of isoxaflutole on the growth, nodulation and nitrogen fixation of chickpea (Cicer arietinum L.)

Isoxaflutole at 75 g/ha is registered in Australia for the control of several broadleaf weeds in chickpea. Although isoxaflutole provides satisfactory control of problematic weeds, under certain conditions crop injury can occur. A controlled-environment experiment was conducted to investigate the extent of isoxaflutole damage on overall growth, nodulation and nitrogen (N) fixation capacity of one isoxaflutole tolerant and one isoxaflutole sensitive chickpea cultivar. Chickpea cultivars were grown under different soil nitrate (NO3-) levels (0 and 1.5 mM), rhizobia treatments (inoculated and uninoculated control) and herbicide rates [0 and 75 g/ha (recommended rate)]. Crop growth, nodulation and N fixation in response to isoxaflutole were assessed 42 days after herbicide treatment. Isoxaflutole at the recommended rate stunted plant growth (29%) and reduced shoot (22%) and root (50%) dry weights of the sensitive cultivar whereas isoxaflutole had no effect on the growth parameters of the tolerant cultivar. Isoxaflutole caused more root damage than shoot damage in the sensitive cultivar. Nodulation (number and dry weight) was also less in the sensitive cultivar when isoxaflutole was applied. Isoxaflutole reduced total N content of the sensitive cultivar by 21%. At the recommended rate of isoxaflutole, the herbicide reduced the N fixation capacity of the sensitive cultivar by 51% compared with the tolerant cultivar (33%) even though both cultivars produced identical amounts of fixed N in the presence of the herbicide. The results suggest that there is a substantial loss in the N fixation capacity of both the tolerant and sensitive chickpea cultivars when isoxaflutole is applied at the recommended field rate. Further work is needed to examine whether the N benefits of chickpea rotations are depleted with the use of isoxaflutole under field conditions. (C) 2009 Elsevier Ltd. All rights reserved.