Field margins are strips of land with grass or flowers on which no crops are grown. They are located between fields or between a field and a ditch. When designed for this purpose, field margins support natural pest control. As a result, there are fewer pests, less crop protection products need to be used, and less of these products end up in ditches. Field margins support the natural control of pests by insects. As a result, fewer pests. The field margins also increase biodiversity and pollination. They also limit the nitrogen and phosphate run off into the ditch. In addition, a more attractive landscape for recreation is created.
The European Union wants to encourage the creation of field margins. RIVM has therefore calculated whether the benefits of field margins outweigh the costs over the course of 30 years (2025-2055). This so-called social cost-benefit analysis (SCBA) was done for the Hoeksche Waard because of its large amount field margins. In this SCBA, the effects on eight themes have been calculated. These include crop production, pollination, pest control, water quality, climate, recreation and biodiversity.
The benefits of field margins for people, nature and the environment appear to be about the same as the costs. Basically, a more attractive landscape and lower costs for the water board to purify surface water outweigh a smaller cropping area and the costs for farmers to create the margins. Two 'benefits' that cannot be expressed in monetary terms and have therefore been assessed ecologically are also greater with field margins. It concerns biodiversity and the self-cleaning capacity of water and soil.
Twelve variants have been calculated for this study in order to be able to take uncertainties into account. Seven of the twelve variants showed higher benefits than costs, such as the effects on health and less crop protection products in ditches, could not be included in this SCBA. If it had, the calculated benefits would probably have been greater. An additional advantage is that field margins along ditches help to achieve the goals of the Water Framework Directive for plant protection products.
The costs now lie mainly with farmers and co-financing government bodies. RIVM sees opportunities to create new revenue models in which the costs and benefits are distributed more fairly among the various parties involved. This can make it more attractive for farmers to build field margins. This SCBA can be used for this.