Coefficients for Modelling the Respiratory Carbon Loss of FIELD-Grown Maize.

Approximately 50% of the carbon fixed by a maize crop is lost again to respiration, but respiratory carbon losses are poorly understood, especially in a field environment. Development of robust mechanistic maize growth models requires a realistic parameterization of respiration in the field. The objective of this study was to estimate crop respiratory carbon loss from measurements of single plant respiratory carbon efflux, crop growth rate and crop dry matter. The experiment was conducted at the University of Guelph Elora Research Station in Ponsonby ON, Canada in 2012. Six treatments were used to create variation in dry matter: 2 inbred lines and their F1 hybrid, sown at 8 and 16 plants m^-2 with 4 replications. On seven dates crop dry matter was measured via destructive harvests and crop growth rate was estimated as the first derivate of a sigmoid function fitted between dry matter and days after emergence.  In the evening on each harvest date three plants per plot with attached roots were collected and moved in pails with water from the field to a dark room, and early the following morning respiration measurements were made.  We found that crop respiration on a ground area basis could be estimated over the entire season using a single function that incorporated the current crop growth rate and the current crop dry matter.  A single function accurately predicted respiration of the inbred lines and their F1 hybrid. Maximum crop growths rate occurred close to flowering, but respiration peaked two weeks after flowering. At physiological maturity the cumulative dry matter loss attributable to respiration was estimated to be 88%, 72% and 71% of the accumulated biomass of the inbred line 1, inbred line 2 and the F1 hybrid respectively.