The Weiherbach data set:: An experimental data set for pesticide model testing on the field scale

There are few consistent and comprehensive data sets for the calibration and verification of computer models of pesticide fate in agro-ecosystems, To partly close this gap the data base of the multidisciplinary Weiherbach research project was used to form a data set that is well suited for that purpose. It has been successfully used during the COST Action 66 model comparison. The Weiherbach research area is a small, intensively cultivated catchment in south-western Germany. The soils of the region are developed from loess and are strongly influenced by erosion. An important feature is the abundance of large macropores that cause preferential flow events. Field dissipation and field lysimeter studies with the herbicide isoproturon and the tracer KBr were conducted in a typical Calcaric Regosol for a late autumn as well as for a spring application scenario. For the lysimeter studies 10 undisturbed soil monoliths (0.45 m long, 0.3 m in diameter) from the same field were used to allow for an estimate of the spatial variability of solute transport. During the spring experiment, one half of the field plot and selected lysimeters were irrigated to simulate wet conditions with higher leaching potential. The Weiherbach data set comprehensively characterises the hydrological, agricultural and soil properties of the experimental sites (including site-specific degradation and sorption data for isoproturon) as well as the meteorological conditions during the experiments. In the field studies, depth profiles of isoproturon and tracer were measured at several dates whereas in the lysimeter studies the percolate was regularly analysed. A detailed description of the experimental results and the whole data set as it was used for the comparison of pesticide transport models within COST Action 66 will be given by Schierholz (1999). In the experiments both matrix and macropore flow occurred and the kind and amount of solute transport clearly depended on the precipitation (irrigation) conditions. The autumn application was followed by an unusually wet winter and represents a 'worst case' scenario with deep leaching of isoproturon. After the spring application there were about average meteorological conditions, but the irrigated variants again represent a 'worst case'. (C) 2000 Elsevier Science B.V. All rights reserved.