Ratios of carbon mass in nodules to other plant tissues in chickpea.

A quantitative measurement of the mass and carbon (C) of nodules in legume crops will provide more accurate estimate of total C entering to the soil. This study quantified the ratios of C in roots and nodules in relation to above-ground plant tissue (AG) for chickpea (Cicer arietinum L.). The cultivars ‘CDC-Anna’ and ‘CDC-Frontier’ were grown in continuously-cropped no-till wheat stubble and conventionally-tilled summer fallow systems under three rates (0, 28 and 84 kg N ha−1) of N fertilizers in Swift Current and Shaunavon, Saskatchewan, Canada, in 2004, 2005 and 2006. The AG biomass ranged between 4,680 and 7,250 kg ha−1 and increased with the application of N fertilizer ≥28 kg N ha−1. The nodule mass measured at the early flowering stage ranged between 143 and 355 kg ha−1, accounting for 2 to 6% of the total AG biomass. Nodule mass decreased significantly from the early flowering to the late-flowering stages (3 wk between). The C value averaged from 1,970 to 2,640 kg ha−1 in the AG parts, 866 to 1,161 kg ha−1 in roots and 82 to 184 kg ha−1 in nodules. The C value in the nodules was 32% greater for chickpea grown in the no-till system than in the tilled-fallow system. CDC-Frontier had 34% greater C value in AG and roots, and 76% greater in nodules than CDC-Anna. Below-ground C (roots plus nodules) accounted for 50% that of the AG tissue at N = 0 kg ha−1, and decreased to 45% as N increased to 84 kg ha−1. At N = 0 kg ha−1, the C allocation among plant parts was in the ratio of 67: 29: 4, respectively, in the above-ground tissues: roots: nodules; at N = 84 kg ha−1, this ratio was shifted to 69: 30: 1. The quantitative C allocation coefficients can be of great value to modellers in estimating total C contribution to the soil by annual legumes.