Marktäckande material som åtgärd för minskat fosforläckage från rasthagar för värphöns

Sammanfattning: Today there is a knowledge gap about phosphorus leakage from free range laying hens, and because of that a pilot project is ongoing since 2016 with scientists at The University of Agricultural Sciences (SLU), Research Institutes of Sweden (RISE) and also advisors in order to investigate the nutrient load from free range laying hens. My thesis have been conducted within this project, and I have chosen to focus on phosphorus leakage. My thesis contains three sub studies. The first sub study consist of a literature study, where factors that need to be considered to assess the risk of phosphorus leakage were investigated. The second sub study included analyses of two ground-stabilising materials for paddocks with respect to phosphorus-binding capacity. The third sub study consisted of measuring the concentration of phosphorous in drainage water at organic farms in Östergötland (south of Sweden). I have in all sub studies decided to focus on the area in the paddock with highest animal density, which usually is the area just outside the stable, often gravelled. Two ground-stabilising materials, sand and lime (CaCO3) were compared with gravel. The materials were spread in paddocks outside the research-stable in the paddock located at the Swedish Livestock Research Centre at Lövsta in Uppsala. After the hens had been in the paddock for a season, sampling of the materials were carried out. The samples were subsequently irrigated using a rain simulator in order to investigate the risk of phosphorus leakage. The water that was leaking from the materials was analysed. The results indicates that the sand and the lime have a higher capacity to absorb and retain phosphorus compared with the gravel. It seems that it mainly is the physical filtering capacity of the materials, rather than the chemical properties of the cover materials, that delay the leakage of phosphorus. That was because both the sand and the lime had higher capacity to absorb and retain phosphorus compared with gravel and no difference could be observed between the sand and the lime. The mean of the concentration of phosphate in the leakage water draining from the samples was 58 mg/l for gravel, 115 mg/l for lime and 136 mg/l for sand. A possible interpretation of this result is that the gravel had lost phosphorus already during the season. This pilot study shows that the phosphorus loading on the water-environment from henspaddocks, in the area closest to the stable is potentially very large. The area closest to the stable is at risk of becoming a point source of phosphorous leakage on the water-environment. Sampling of drainage water in the field could give an estimation of the amount of phosphorous leakage from hen paddocks.