The Importance of Phosphorus

• Phosphorus is a critical part of plant energy transfer functions and other cellular functions within the plant, according to University of Arizona extension agent Jeff Schaulau. Plant roots take up phosphorus in the form of phosphate ions and quickly transfer it throughout the plants from roots to leaves. Phosphorus is the second letter, P, in the N-P-K formula listed on fertilizer bags. These formulas tell the purchaser what percentage of phosphorus is in the fertilizer mixture. When this P number is higher than the others, the fertilizer is high in phosphorus and can help correct phosphorus deficiencies in garden soil.
  
  

Phosphorus Deficiency

• Symptoms of phosphorus deficiency in plants include reduced growth, darker-than-normal or purple foliage, weak stems, limited lateral bud growth, reduced flowering and fruiting and the loss of lower leaves on stems. If these symptoms appear in your plants, adding additional phosphorus to your soil will help to correct the problem.
  
  

Adding Phosphorus to Soil

• Phosphorus comes in both organic and chemical forms. Organic sources of phosphorus include vermicompost, that is, manure digested by worms, rock phosphate and bone meal, according to Colorado State University soil specialists A.L. Elliot et al. Chemical phosphorus fertilizer is made first with the production of phosphoric acid. This substance is then heated and then treated with ammonia to combine phosphorus with nitrogen. Fertilizers containing high percentages of phosphorus should be applied only as needed to correct soil deficiencies. Excess amounts of phosphorus in the soil can be detrimental to both plants and the environment.
  
  

Phosphorus & the Environment

• Phosphorus is held in the soil, resulting in reduced need for additional amounts over time. Excess phosphorus is not easily leached out of soil. When soil is washed into local waterways by rainfall and flooding, the phosphorus causes "eutrophication," an explosive growth of algae. As this large amount of algae decomposes, it restricts the amount of oxygen available for fish and other aquatic life forms, which can disrupt entire ecologies of plant and animal life. Phosphates can also find their way into the groundwater that humans use. Gardeners and homeowners should use phosphorus fertilizers with great care to prevent the environmental disruption and high cost of restoring these waterways to health.