| Abstract: | Budgets for C and N were computed for pigeonpea (Cajanus cajanL.) at 15 d intervals, for the entire life cycle. Maximum Cand N in dry matter was observed at 90 d after sowing. Of theplants total respiratory loss during the vegetative phase, shoots,roots and nodules accounted for 65%, 23% and 12%, respectively.During the reproductive phases, the respiratory burden of theroots increased, while that of shoots and nodules decreased.Total respiratory loss as a proportion of net photosynthateremained more or less constant until ‘flowering and pod-setting’but increased heavily during seed filling, losing nearly 75%of the photosynthate in respiration. The efficiency of nitrogenfixation, in relation to respiratory output of the whole plantand nodulated roots, decreased during the period 60–90d after sowing, while that of nodules decreased from day 45onwards. Photosynthate supply to nodules and nodulated rootsincreased up to 75 d and 90 d after sowing, respectively. During45–90 d, nodules were fixing a constant proportion ofN per unit of C translocated (0.2 mg N mg–1 C). Nodulatedroots, on an average, fixed 0.07 mg N mg–1 C translocatedin the vegetative phase and this value decreased considerablyduring the subsequent phases. The crop produced during its lifecycle 50.4 g of glucose equivalents and yielded 3.8 g seed drymatter and 0.8 g seed protein giving an average of 13.2 g g–1seed dry matter and 62.8 g g–1 seed protein. Selectioncriteria for the improvement of C, N economy in pigeonpea havebeen suggested. Key words: Cajanus cajan, Carbon, Nitrogen, Dry weight, Plant parts, Growth, Development, Models |
