Phosphorus is a key element in biological reactions so that small changes in phosphorus availability can have major impacts on ecosystem function and structure. In soils and ecosystems, P is derived from the parent rocks. Although phosphate is relatively insoluble it is eventually weathered and leached out so that many old soils are P deficient and their associated ecosystems are P limited. High productivity agriculture relies on P fertilisation. Phosphorus is highly concentrated in plant seeds (grains), animals and animal (and human) excrements. Consequently environments with intensive animal production or high population density receive a surplus of P that commonly causes environmental pollution. The imbalance between regions of low and of surplus P must be addressed through more efficient P management, both in fertilisation practices and efforts to recycle P from wastes. This is particularly important as the principal source of P, rock phosphates are becoming more expensive, reserves more difficult to find and mine, and are globally strategically unevenly distributed.

Key Concepts:

• The only source of P in soils are the parent rocks or added fertilisers.
  
• Weathering slowly removes P from soils, so that many old and tropical environments are P deficient.
  
• P is essential to all life and is concentrated by organisms to levels thousands of times higher than environmental concentrations.
  
• High environmental P concentrations usually result from the excretions or residues of organisms.
  
• Being limiting to life, P stimulates biological growth and when in excess will cause ecosystem disruptions through eutrophication.
  
• The principal source of fertiliser P are rock phosphates which are sedimentary deposits of marine organisms.
  
• Approximately 1000 million t of P have been mined and added to the environment.
  
• Finite P resources have caused concern about ‘peak production’ occurring near the middle of the twenty-first century, followed by declines and higher prices that may limit food production.