SOWING TIME AND TILLAGE PRACTICE AFFECT CHICKPEA YIELD AND NITROGEN-FIXATION .2. NITROGEN ACCUMULATION, NITROGEN-FIXATION AND SOIL-NITROGENBALANCE

Following long-term studies at Warra, on the western Darling Downs, ch ickpea (Cicer arietinum) was selected as a useful grain legume cash cr op with potential for improvement of its nitrogen (N) fixing ability t hrough management. This 2-year study examined the effect of sowing tim e and tillage practice on dry matter yield, grain yield (Horn et al. 1 996), N accumulation, N-2 fixation, and the subsequent soil N balance. Generally, greater N accumulation resulted from sowing in late autumn -early winter (89-117 kg N/ha) than sowing in late winter (76-90 kg N/ ha). The amount of N-2 fixed was low in both years (15-32 kg N/ha), an d was not significantly affected by sowing time or tillage. The potent ial for N-2 fixation was reduced in both years due to high initial soi l nitrate levels and low total biomass of chickpea because of low rain fall. Nitrogen accumulation by grain was higher under zero tillage (ZT ) than conventional tillage (CT) for all sowing times, and this affect ed the level of grain N export. The consequence of low N-2 fixation an d high N export in chickpea grain was a net loss of total soil N, (2-4 8 kg N/ha under CT and 22-59 kg N/ha under ZT). Management practices t o ensure larger biomass production and lower soil nitrate-N levels may result in increased N-2 fixation by chickpea and thus a positive soil N balance.