Nitrogen dynamics of chickpea: Effects of cultivar choice, N fertilization, Rhizobium inoculation, and cropping systems

Abstract

Understanding N dynamics in relation to cultural practices may help optimize N management in annual legume crops. This study was conducted at six environsites (location × year combinations) in southern Saskatchewan, 2004-2006, to quantify N uptake, N2 fixation, and N balance in chickpea (Cicer arietinum L.) in relation to cultivar choice, cropping systems, rhizobial inoculation, and soil N fertility. The cultivars Amit, CDC Anna, CDC Frontier, and CDC Xena were grown at N fertilizer rates of 0, 28, 56, 84, and 112 kg N ha-1 with no Rhizobium and at 0, 28, and 84 kg N ha-1 combined with Rhizobium inoculation, evaluated in both conventional tilled-fallow and continuously cropped no-till systems. Flax was used as a non-N-fixing reference crop. The cultivar CDC Xena had the lowest yield (1.57 Mg ha-1) and seed N uptake (54.4 kg N ha-1), with N use efficiency (NUE, 13.2 kg seed N kg-1) being 17% less than the average of the other cultivars. Consequently, N balance (N input via fertilizer and N-fixation minus N exported) was -32.4 kg N ha-1 for CDC Xena and less negative than the average of the other cultivars (-39.8 kg N ha-1). Inoculated chickpea took up 10 kg ha-1 more N into the seed and 5 kg ha-1 more N into the straw than chickpea that was not inoculated. The amount of N fixed as a percentage of total N uptake was 15% for non-inoculated chickpea and 29% for inoculated chickpea, resulting in negative N balance regardless of cropping system. Increasing N fertilizer rates decreased NUE, with the rate of decrease being greater for non-inoculated chickpea compared with inoculated chickpea. We conclude that optimum productivity of chickpea can be achieved with application of effective Rhizobium inoculants, and that best N management practices must be adopted in the succeeding crops due to a large negative N balance after a chickpea crop.Key words: Chickpea, Cicer arietinum, N fertilizer, N2 fixation, Rhizobium inoculants, N balance, nitrogen use efficiency, N uptake