Long-term trends in phosphorus leaching and changes in soil phosphorus with phytomining

Few mitigation strategies exist to reduce phosphorus (P) losses in leachate once soil P has built up. "Phytomining," or harvesting a crop without application of fertilizer P to create a negative P balance, has been proposed as a strategy for lowering soil P levels and preventing P loss to runoff and leachate. In this study crops were grown and harvested over 7 to 16 years in undisturbed soil columns (105 cm [41 in] deep) with contrasting textures (loamy sand, sandy loam, silty clay loam, and clay) and high P levels, while P loss in leachate was measured. Soil test P in the topsoil (0 to 20 cm [0 to 8 in] depth) was significantly decreased from the beginning to the end of the study for all soils, while a significant decreasing trend in dissolved reactive P in leachate was only observed in one soil. Downward movement of P from the topsoil to deeper layers was indicated to occur in three out of four soils. Although phytomining lowered soil test P by 11% to 37% in topsoils over the 7 to 16 year period of the study, results indicate that soils with P content well above agronomic optimum may take a much longer time to reach the agronomic optimum.