Original paper

Soil structure and herbicide transport on soil surfaces during intermittent artificial rainfall

Ulrich, Uta; Zeiger, Marcus; Fohrer, Nicola


The application of simulated rainfall is an appropriate method to investigate processes taking place at the soil surface under defined conditions. Exemplarily for the use of a rainfall simulator, two studies are described observing the effects of intermittent rainfall on the soil surface structure of three soils of different management systems (SSS) and the herbicide transport (HT) via surface runoff. In both studies, soil boxes (90×80×40 cm) were exposed to 10×15 mm (SSS) and 6×13 mm (HT) rainfall with each six rainless days in between. Runoff and erosion effects were observed as well as the breakdown of soil aggregates and crusting of the soil surface. In the SSS study, soil surface crusting process started earlier in the conventionally managed soil than in the soils from the organic farming system. Additionally, the soil surface of the conventional and organic managed soils was similarly sealed at the end of the experiment, but the well-established organic farming management showed lower runoff during all rainfall events than the recently established organic farming management. Both soils from the organic farming systems showed lower surface runoff and higher water infifiltration capacity than soils from the conventional management system. In the HT study, highest herbicide concentrations were observed in the first interval of surface runoff while maximum loads occurred during the second rainfall event. Concentrations in the water phase of the surface runoff were up to 3184 μg metazachlor/l, 661 μg terbutylazine/l and 207 μg flufenacet/l. During the six rainfall events, the discharged herbicide loads in the two parallel boxes amounted to 1.7-2.2 mg metazachlor/m², 1.5-1.6 mg terbutylazine/m² and 0.5-0.6 mg flufenacet/m². These loads correspond to 1.9 and 2.5% (metazachlor), 5.7 and 6.6% (terbutylazine) and 2.1 and 3.8% (flufenacet) of the amount applied. During the rainless periods, physical and chemical alterations of the soil surface occurred and caused an increase of herbicide concentration in first interval of each following rainfall event.


intermittent rainfall experimentssoil surface aggregationrunoffinfiltrationherbicidessoil managementorganic farmingconventional farming