Controlling indeterminate lentil crop growth through nitrogen supply

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Lentil is an indeterminate pulse crop, which means it has a growth habit where vegetative growth continues during reproductive growth.  In contrast, the determinate habit has a vegetative phase followed by a distinct switch to reproductive growth, for example, in grasses.  In wet years and when it has a high nitrogen (N) supply, lentil fails to mature in the short growing season on the Prairies, resulting in low unstable yields.  Because a determinate lentil genotype has not yet been found, we believe an agronomic approach of controlling the balance between vegetative and reproductive growth through crop N supply may provide a solution to this delayed maturity.  On the Prairies, the indeterminate habit is managed by relying on either a terminal stress (drought, frost, lack of N) or chemical desiccation to cease growth.  Lentil can derive most of its N through biological N fixation, a symbiotic relationship between rhizobia bacteria and the plant that takes place in nodules on the roots.  Lentil can also use fertilizer N, or soil supplied N through the process of soil mineralization.  Growers depend on N fixation, but soil inorganic N may be available depending on the previous soil history, climate and mineralization.  In this research, we plan to investigate how lentil indeterminacy can be managed by four strategies.  The first is to test if lentil maturity can be controlled by soil N supply in zero tillage and conventional tillage soils.  The second is to test if a desiccant at low concentrations can trigger senescence and maturity under high N conditions. The third strategy is test if nine lentil genotypes that are commercially grown vary in N uptake, N fixation, or N redistribution within the plant during reproductive growth.  Finally, the fourth strategy is to identify earlier senescing rhizobia strains so N fixation will only occur up to mid-reproductive growth.  Together, all these strategies will give us a detailed understanding of how N is partitioned in lentil in order to have satisfactory crop maturity.