Dominique Flura

Measuring ammonia fluxes after slurry spreading under actual field conditions

Abstract A large fraction of atmospheric ammonia is emitted during the application of slurry to fields. Two micrometeorological methods were used to obtain a consistent estimate of emissions under actual field conditions. The mass balance method (MBM) was used to quantify the very large emissions that occur during slurry spreading and for the first few hours. Wind speed was measured at 5 heights, and ammonia was sampled at these heights by trapping it in dilute sulphuric acid. A two-height aerodynamic gradient method (2AGM) was used for later automated hourly monitoring of the long-term flux over a large surface (over a hectare). The ammonia concentration gradient was measured continuously with a chemiluminescence analyser. The hourly estimates of ammonia fluxes were similar to the data from a labelled nitrogen recovery method (15NRM). The MBM gave reliable flux estimates using only two measurement heights. Thus, ammonia fluxes could be determined directly in real time using the chemiluminescence analyser, and two air temperature measurements by two anemometers, beginning from the first minutes after the start of slurry spreading, and continuing until several weeks later.

Influence of simulated rain on dispersal of rust spores from infected wheat seedlings

Spores of both Puccinia recondita f. sp. tritici and P. striiformis (brown rust and yellow rust of wheat) are thought to be primarily dispersed by wind. The results of experiments, using a rain simulator with uniform drop sizes (2.5, 3.4, 4.2 or 4.9 mm), on the effect of rain on dispersal of brown (leaf) rust and yellow (stripe) rust spores are reported. Experiments on both pathogens were done in still air; additional experiments were done on brown rust with simulated wind and rain. Spore dispersal was estimated by trapping spores on wheat plants and assessing the disease symptoms which subsequently developed under optimum conditions. Simulated rainfall of each the four drop sizes tested dispersed spores of both pathogens. In still air spore dispersal patterns were similar to those usually found for pathogens which are characteristically splash-dispersed. Rain exhausted the source of spores in about 20 min for the four drop sizes. When the plants were kept under optimal conditions for sporulation, the source of brown rust spores available for dispersal was restored to its initial numbers in about 2 h after depletion. For yellow rust, spore numbers in the source had not been restored to their original value after 6 h, even under optimal conditions. In the wind tunnel experiments, simulated rain did not inhibit the dispersal of brown rust spores by wind. Large incident drops dispersed more spores of both pathogens than small drops. A simulation study based on the experimental relationships obtained was done. Although these experiments clearly show that rainfall has the potential to spread both brown rust and yellow rust of wheat, the understanding of the exact role of rain dispersal in the epidemiology of both diseases requires further investigation.

Fungicide Volatilization Measurements: Inverse Modeling, Role of Vapor Pressure, and State of Foliar Residue

Few data sets of pesticide volatilization from plants at the field scale are available. In this work, we report measurements of fenpropidin and chlorothalonil volatilization on a wheat field using the aerodynamic gradient (AG) method and an inverse dispersion modeling approach (using the FIDES model). Other data necessary to run volatilization models are also reported: measured application dose, crop interception, plant foliage residue, upwind concentrations, and meteorological conditions. The comparison of the AG and inverse modeling methods proved the latter to be reliable and hence suitable for estimating volatilization rates with minimized costs. Different diurnal/nocturnal volatilization patterns were observed: fenpropidin volatilization peaked on the application day and then decreased dramatically, while chlorothalonil volatilization remained fairly stable over a week-long period. Cumulated emissions after 31 h reached 3.5 g ha(-1) and 5 g ha(-1), respectively (0.8% and 0.6% of the theoretical application dose). A larger difference in volatilization rates was expected given differences in vapor pressure, and for fenpropidin, volatilization should have continued given that 80% of the initial amount remained on plant foliage for 6 days. We thus ask if vapor pressure alone can accurately estimate volatilization just after application and then question the state of foliar residue. We identified adsorption, formulation, and extraction techniques as relevant explanations.