Sowing time and tillage practice affect chickpea yield and nitrogen fixation .2. Nitrogen accumulation, nitrogen fixation and soil nitrogen balance

Following long-term studies at Warra, on the western Darling Downs, chickpea (Cicer arietinum) was selected as a useful grain legume cash crop with potential for improvement of its nitrogen (N) fixing ability through management. This 2-year study examined the effect of sowing time and tillage practice on dry matter yield, grain yield (Horn et al. 1996), 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), and was not significantly affected by sowing time or tillage. The potential for N 2 fixation was reduced in both years due to high initial soil nitrate levels and low total biomass of chickpea because of low rainfall. Nitrogen accumulation by grain was higher under zero tillage (ZT) than conventional tillage (CT) for all sowing times, and this affected the level of grain N export. The consequence of low N 2 fixation and high N export in chickpea grain was a net loss of total soil N, (2-48 kg N/ha under CT and 22-59 kg N/ha under ZT). Management practices to 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.