The distribution of carbon dioxide released from a ground level area source in a field crop and its predicted influence on crop assimilation

Abstract

The primary objective of this research was to evaluate the physical and physiological feasibility of COâ‚‚ enrichment in field crops. Specific objectives were 1) to find a method of predicting the COâ‚‚ distribution from an area source at ground level in a crop, and 2) to predict the crop carbon dioxide assimilation rate and water use when COâ‚‚ is released. A model of the COâ‚‚ distribution (DIFFUSION) was developed. The model was based on the two-dimensional steady state diffusion equation combined with wind and eddy diffusivity profiles above and within the crop canopy. The model was used to compute the COâ‚‚ concentration at a given space grid point as a function of wind speed in the surface boundary layer, ambient COâ‚‚ concentration, COâ‚‚ release rate and the aerodynamic canopy parameters (canopy height, zero-plane displacement, roughness length, and an exponential coefficient of within-canopy wind profile). The model was tested by an area source COâ‚‚ diffusion experiment in a cotton canopy. The measurements showed that the model effectively predicted the COâ‚‚ profile for a dense and homogeneous canopy under neutral conditions. The DIFFUSION model was combined with CANOPY-LAM-II, a steady state one-dimensional model of mass and energy exchange by a crop canopy, based on the Duncan-Stewart radiation model and a leaf action model. The CANOPY-LAM-II-DIFFUSION model calculated the crop carbon dioxide assimilation rate and water use as a function of the environmental conditions (wind speed, air temperature and dew point above the canopy, COâ‚‚ concentration in the non-release area, global irradiance, and the effective soil water potential), the COâ‚‚ release rate, and the aerodynamic, optical and physiological characteristics of the canopy. ...