Hur lutar åkermarken mot angränsande diken? Pilotprojekt kring att använda SLU:s dikeskartor för att förbättra indata till fosforläckagemodellen i NLeCCS-systemet

The model ICECREAM is used in calculating phosphorus losses from Swedish agricultural soils within the calculation system NLeCCS. The slope of the field is one of the governing factors. The calculations are made with the assumption of square fields with a linear slope towards a ditch along one side of the field. The project has used the SLU ditch maps and calculations of field properties to investigate how well this assumption fits the reality.
The farmer’s blocks with arable land are best described as a rectangle sloping towards the shorter side. The assumptions within the NLeCCS-system can be used also onwards since the phosphorus losses are rather similar between rectangular fields sloping towards the short side and square fields. Further studies of the influence on the phosphorus losses from drainage wells on the fields is however recommended.
Roughly the farmer’s blocks only have a ditch along one side. It does however vary between individual fields and across the country. The ditches may also be e.g. border ditches and not ditches which the fields are draining towards. The ditch maps show open ditches and not culverts and tile drainage. The ditch maps are useful to understand the placement of the open ditches in the agricultural landscape, although they probably cannot be used directly as input data to NLeCCS.