Nutrient Cycles
What Are the Processes and Features of the Phosphorous Cycle?
The Phosphorous Cycle
Phosphorus is an important element to all living organisms. It is a major component of nucleic acids, phospholipids, and ATP. It is also an important component of animal bones and teeth. In contrast to carbon and nitrogen, phosphorus is not present in a gaseous form in the atmosphere. The greatest quantities of phosphorus are found as minerals in oceanic rock. Large amounts are deposited on the ocean floor.
The phosphorus cycleglossary term (opens in a new window) involves the transfer of phosphorus, primarily in the form of phosphate (PO43–) between rocks, soil, water, and organisms. The weathering of rocks is the primary way that phosphate enters the soil. Plants absorb phosphate through their roots. Animals obtain the phosphorus they need from eating plants and other food. Phosphorus is returned to soil by decomposition and waste from organisms. Phosphorus compounds are lost from the soil in runoff.
Farmers and gardeners replace phosphorus compounds lost from the soil using manures and fertilizers. Bone meal is one important source of phosphorus compounds that is used by gardeners. Most farmers use inorganic fertilizers rich in phosphates. As with nitrogen, over-fertilization can add too much phosphorus to soil and water. In water, too much phosphorus can cause algae to overgrow and die. When microorganisms decompose the algae, they use oxygen in the water. Without enough oxygen, fish and other organisms in the water may die.
Teacher Note: Practices
In this item, students will think about how technology can be used to improve farming. They analyze data using tools in order to determine an optimal design solution. Before students complete this item, help them study how fertilizers flow from farms by demonstrating a model of how water moves from farmland. Place dirt in a box and pour water over it. Ask them where the water goes. What strategies prevent water carrying phosphate from flowing away from the dirt?
