Reducing flood risk from sediment-laden agricultural runoff using intercrop management techniques in northern France

Abstract

To reduce muddy flooding in northern France, where soils are typically silty and highly sensitive to crusting, it is necessary to decrease the volumes of sediment-laden runoff coming from upslope agricultural source areas. To investigate the consequences of upslope agricultural practices on downslope muddy flooding, we compared the effects of no-tillage treatment (NT), light-duty mouldboard ploughing (PLOUG), mustard ( Sinapis alba L.) intercrop (MUSTA) and superficial tillage with a cultivator applied either under dry (ECULT) or humid conditions (LCULT). The influence of these different treatments were measured on soil surface modifications and on both runoff and sheet erosion during the entire intercrop period. Field trials were conducted in the Pays de Caux (Normandie), over two years (1993–1994 and 1994–1995) under natural rainfall conditions on 20 m 2 experimental plots on Orthic Luvisols. In 1993–1994, the post-harvest field conditions were wheat ( Triticum aestivum L.) with pulverized straw, wheat without straw and pea ( Pisum sativum L.) without straw. Only the pea post-harvest conditions were used in 1994–1995. The tortuosity index and percentage of surface area covered by vegetation, which were used for soil surface description, indicate the role played by surface cover and soil water during tillage in modifying surface roughness. In 1994–1995, due to specific agronomic and climatic conditions, the five intercrop management techniques did not differ significantly at P < 0.10 for runoff and erosion. In 1993–1994, considering average values for both the three post-harvest conditions and 10 recorded rainfall events, NT resulted in low erosion (40 kg ha −1) but high runoff (6.1 mm). Compared to NT, MUSTA significantly ( P < 0.10) reduced runoff (1.5 mm) without significantly increasing erosion (82 kg ha −1); LCULT led to an increase in both runoff (12.4 mm) and erosion (301 kg ha −1); PLOUG increased erosion (182 kg ha −1) but reduced runoff (3.2 mm) and ECULT increased erosion (247 kg ha −1) without reducing runoff (7.1 mm). These results specify the dynamics of runoff and sheet erosion, thus providing an aid for locating intercrop management techniques within a catchment basin according to the local erosive system and agronomic constraints.