ABSTRACT
As a surrogate for photosynthesis, biomass accumulation at the crop level can be estimated from the product of the amount of radiation intercepted and the amount of dry matter produced per unit of radiation intercepted (radiation use efficiency, RUE). The cotton crop simulation model CERCOT uses this approach and modulates RUE in response to canopy nitrogen status. However, the response of RUE of cotton to its nitrogen status is uncertain. Using a previously reported approach to scale from leaf photosynthesis to canopy RUE, we explored the significance of developmental changes in the vertical distribution of canopy N and canopy light interception characteristics on the response of RUE to nitrogen status. Tested against a field experiment, the framework performed reasonably well for high observed RUEs but over-estimated low RUEs. A number of avenues are being explored to improve its performance. A sensitivity analysis with the framework suggested that RUE in cotton was not effected by developmental changes in the vertical distribution of canopy N or light interception characteristics, but this needs to be tested in cotton crops with larger canopies where these effects are likely to be more important.

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