Identifying sources and sinks of scalars in a corn canopy with inverse Lagrangian dispersion analysis II. Ammonia

An inverse Lagrangian dispersion analysis was used to infer sources and sin ks of ammonia (NH3) in the canopy of a dense corn crop (LAI similar to 5) s ubject to frequent sprinkler irrigation with dairy effluent. Source strengt hs were calculated for four canopy layers using statistics of the canopy tu rbulence and measurements of atmospheric NH3 concentrations at six heights within the canopy and two above it. The analysis was performed for 4 days of measurement, two immediately follo wing and two several days after effluent application. The analysis provided estimates of the net loss of NH3 from the canopy, which agreed well (withi n 20%) with conventional aerodynamic estimates of the flux of NH3 in the cr op boundary layer. In addition, it permitted an examination of processes of loss within the canopy. Small, but not insignificant NH3 losses were infer red for the soil. These ranged from 4% of the total loss several days after effluent application to 30% on the day of application. Unexpectedly large losses occurred from the foliage in the top half of the canopy. Calculation s of apparent ammonia compensation points for the corn leaves indicated tha t even days after the surface water had evaporated, compensation points wer e too high for the loss to be explained by diffusion through stomata. It wa s surmised that the loss was from residues remaining on foliage surfaces. V olatilization losses from the developed crop were estimated to be about 30% of the N applied, 18% coming from soil and foliage and 12% from spray loss es during effluent application. Published by Elsevier Science B.V.