Planning work constraints within farms to reduce runoff at catchment level

In the loam belt of Northern Europe and in the North-western Paris Basin, runoff and erosion may be reduced by changing agricultural practices in the agricultural catchment where runoff is produced. However, such changes may be limited by work planning constraints at the farm level. This study therefore aimed to assess farmers' leeway to introduce stubble ploughing and mustard (Brassica alba) sowing during the intercrop period. The case study was the Bourville catchment (1086 ha), cultivated by 28 farmers and located in Pays de Caux, France. Firstly, workload was analysed and sequences of cultivation operations were simulated for an average climate for the 14 main farms located in the catchment. This analysis was based on surveys carried out with farmers. It was then possible to determine the number of working days available to perform stubble ploughing and mustard sowing, both of them being efficient practices to reduce runoff at the field level. Results showed that farmers did not have the same leeway as some of them were even unable to perform stubble ploughing or mustard sowing. Then at the catchment level, the impact of changes in agricultural practices on runoff volume at the catchment's outlet was simulated by using the STREAM model. These simulations showed that not taking into account work planning constraints within farms led to overestimating both the possibilities of implementing changes in farms and the efficiency of such changes on runoff reduction.