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Manure management and increased soil phosphorus levels are issues faced by many dairy farmers. A method to reduce the phosphorus content of dairy lagoon effluent is needed to allow continued effluent application for nitrogen and irrigation water without exceeding the phosphorus needs of the crop. This study examined the feasibility of using electric arc furnace (EAF) steel slag to remove phosphorus from dairy lagoon effluent. Treatment columns filled with EAF steel slag had dairy lagoon effluent added with a 12-hour retention time batch flow over a course of 106 days. Samples were collected weekly and analyzed for dissolved reactive phosphorus and pH. Differences between the influent and effluent for each treatment column were determined. Four treatments were compared: warm temperatures, cold temperatures, high organic content, and a gravel control. Significant differences were observed among treatments. Cold temperature resulted in the greatest phosphorus removal efficiency, followed by high organic content, warm temperature, and the gravel control. Among the EAF steel slag treatments, the average overall phosphorus removal efficiency for the 106-day study ranged from 63% -71%.