ARE LEGUMES DOING THEIR JOB? THE EFFECT OF HERBICIDES ON N_2 FIXATION IN SOUTHERN AUSTRALIAN AGRICULTURAL SYSTEMS

摘要

Grain and pasture legumes are an integral part of cropping systems in southern Australia. They can (i) act as a break crop for cereal root diseases, (ii) offer an opportunity to control grass weeds through the use of herbicides and (iii) increase soilnitrogen (N). The culmination of these benefits generally results in improved cereal yields following a legume crop (Khan et al. 2003). However, in the dryland fanning regions of southern Australia (the Mallee), legumes have failed to provide the 'expected' N benefits, due primarily to low N_2 fixation (about 25% that of expected) (Gupta, V.V.S.R., CSIRO, personal communication). The aim of this research was to determine if recommended post-emergent herbicides affect the legume-rhizobia symbiosis, andthereby the soil N balance.