Most studies show that simplified rotation systems tend to lead to an increase in the use of pesticides and therefore to an increase in the transfer of pesticides to the environment.
For instance, Andert et al. (2016) analysed whether diverse cropping sequences and ploughing would reduce herbicide and fungicide use in arable farming on 60 farms in four regions of Northern Germany using a 2005-2014 dataset. They classified different three-year crop sequences based on literature and expert knowledge into five different categories of crop health riskiness (very high to very low). The highest risk was associated with a high proportion of winter cereals in a crop sequence, increasing the risk for take-all (Gaeumannomyces graminis var. tritici), leaf spots (wheat after wheat), stem base and leaf diseases (barley after barley).
Simplified cropping patterns that are susceptible to risks by pests and diseases dominate almost 50% of the current arable land use in Northern Germany (Steinmann and Dobers, 2013) and in the Paris basin, where wheat can be cultivated three time in five years (Agreste, 2010). Most diversified cropping patterns depend less on herbicide and fungicide use and on ploughing, showing a lower number of treatments. Weeds and diseases were effectively managed with diversified crop sequences even under no-ploughing tillage systems. Simplified rotations were characterized by high pesticide application, especially in non-ploughed cropping systems.
Various mechanisms as reason for low pest densities have been explored in mixed vegetation in comparison to monoculture, such as altered plant odor due to physiological changes in the plant (Finch and Collier, 2000), and alterations of herbivore insect reproduction cycles.
Cropping patterns are reported from the Member States to Eurostat (Eurostat 2018).
National data, maps and statistics (i. e. Thünen Atlas ”Landwirtschaftliche Nutzung”) on crop cultivation areas, linked to data on pesticide sales and usage in different crops according to Statistics regulation (EC) No 1185/2009 (i. e. Rosberg, 2016) could built the basis for calculations of regional pesticide application. These data should be available in all Member States. Data on crop cultivation areas could also be linked to fertiliser need of crops (and possibly further data on soil properties and organic fertiliser supply) to verify if there is a link between plant need, N-application and water pollution with nitrates.
Therefore, the (local) cropping pattern would be an indicator suitable to combine with other data. As a simplified approach, the percentage of intensively cultivated crops could serve as indicator, e. g. % winter wheat in Northern Europe and the % maize in Southern France and Northern Italy.