Title: The effect of Lathyrus japonicus on soil fertility in Iceland

Nitrogen is the most limiting nutrient in agriculture and degraded land. Biological fixation of atmospheric nitrogen by legumes is an efficient process that supplies large amounts of nitrogen to soil. This study focuses on assessing the effectiveness of Purple beach pea in improving the fertility of degraded soils in the Hekluskógar area in South Iceland. The objectives were to determine the effects of Purple beach pea on (i) selected soil chemical properties such as C, N, P, Ca, Mg, K and pH, and (ii) the growth rate of the ryegrass Lolium xhybridum in soils where Purple beach pea has grown compared to soil where Purple beach pea is absent in a greenhouse experiment. Soil samples were collected at 0-5 cm and 5-15 cm at randomly selected sites where Purple beach pea has been growing for the last 15 years (treated) and control sites (untreated) at Hekluskógar. Soil samples were analysed for carbon and nitrogen using the Dumas method. Other measurements included phosphorus, calcium, magnesium, potassium, pH, and C:N ratio. The top 15 cm of soil was collected from both treated and untreated sites and used in a greenhouse experiment, where 25 seeds of ryegrass were seeded in eight separate pots for each treatment. The height of ryegrass was measured and the biomass was measured after drying in an oven. The results showed that treated sites had significantly (p < 0.05) higher total soil nitrogen and carbon content in 0-5 cm compared to the untreated sites. Also, the oven-dried biomass of the ryegrass was significantly (p <.0015) higher in the treated soil than untreated soil. This study thus demonstrated the beneficial effects of Purple beach pea on soil nitrogen and carbon plus beneficial effects on growth rates of ryegrass. This clearly shows that Purple beach pea could be important in revegetation of eroded land in Iceland.