Olika filtermaterial vid jordbruksdränering

Abstract: Drainage of arable land creates a better soil structure and a better aeration of the soil profile. Some fields are naturally drained, while others are dependent on drainage to create good cultivation conditions. Subsurface drainage is the most common method used to artificially drain arable land. Various types of filters are used to protect the buried drainage pipes. The task of the filter is, in addition to protecting the pipes, to reduce the sedimentation of particles in the pipes and to facilitate water intake. The different filter materials are usually divided into three categories; mineral filters, organic filters and synthetic filters. The category mineral filters include gravel and the category organic filters include peat, sawdust and coconut fibers. Synthetic filters are made of different types of plastic materials. In Sweden, gravel is the most widely used filter material. In a filter trial at Härna outside Linköping, it was studied how different types of filter material affect the sludge deposition in the drainage pipes and the drainage systems durability in the long term. The filter trial consists of 10 lateral pipes and the filter materials include gravel, coconut fiber, peat and synthetic fiber. Collection of sam-ples were done on November 27, 2018. For each excavated drainage pipe, two soil samples were taken, one sample of sedimented material from within the pipe and one sample just outside the pipe, as well as a gravel filter sample, which was then analyzed in the laboratory. The particle size analysis showed that the drainage pipes with gravel filter release most coarse material from the examined pipes. This is probably due to the gravel contains relatively large pores. The result of the particle size analysis also showed that the proportion of clay inside the drainage pipes is considerably lower than outside the pipes. One explanation for this may be that clays form aggregate structures. When selecting filter materials, the advantages should be weighed against the disad-vantages. Organic filters are advantageous to use as organic material is a renewable resource. However, organic filter materials can be decomposed by microorganisms in the soil, which is not the case with gravel and synthetic filters. A disadvantage of synthetic filters may be that they can release microplastics in nature. The release of microplastics from synthetic filter materials is a proposal for future research.