Nodulation and nitrogen fixation (acetylene reduction) of four cultivars of chickpea

Abstract

The capacities of 4 Australian cultivars of chickpea to nodulate, grow and to fix N2 after inoculation with commercial peat inoculant (Group N, strain CC1192) were examined up to flowering in 2 experiments. One was a field experiment and the other a glasshouse pot experiment involving application of mineral (NO-3) N. Nodule activity was estimated by acetylene reduction assay (AR). The study was conducted in response to recent reports and field observations of apparently poor fixation by chickpea crops in South Australia and of poor cereal yield following a chickpea crop. The cultivars Dooen, Tyson, Opal and Amethyst all nodulated successfully with the inoculant and fixed N2 actively over the vegetative period, although plants were slow to nodulate under warm conditions. A sharp decline in nodule activity was not observed at flowering but observations were not continued into the grain-filling period. A nutrient solution 2.5 mmol/L for NO-3 (compared with no NOT) applied 14 days after sowing, delayed nodulation, had no effect on total nodule number 50 days after sowing but markedly reduced nodule activity of all cultivars. Cultivars showed only small differences in nodule number and in nodule activity; but all showed a strong, positive, growth response to NO-3 and accumulated more N when NO-3 was applied than when only N2 was fixed. It was concluded that all 4 cultivars were adequately nodulated by strain CC1192, which led to active N2 fixation during the vegetative period. Poor apparent fixation by chickpea crops in the field may be due to decline in nodule activity during grain filling and mobilisation of plant N to the grain, or to the use of soil mineral N rather than fixed N2. If chickpea is to gain a useful place in cereal-grain legume rotations in southern Australia, grain yield needs to be increased, dependence on soil N reduced and nodule activity prolonged into the grain filling period. These objectives may be achievable in part through the identification and eventual use of an inoculant other than CC1192.