Figure 21.8 The phosphorus cycle. Phosphate rocks that are uplifted by geologic forces naturally weather over time to release phosphorus. These rocks are the source of phosphorus used in fertilizer and detergents. Phosphorus is taken up by producers and moves through the food chain until it is released either through waste or decomposition. Excess phosphorus on land runs off the surface or leaches out of the soil and into aquatic habitats. In the ocean, phosphorus combines with calcium or iron and precipitates out of the water column, ultimately to form phosphate rocks again.