Phosphorus in agriculture, a limited resource.

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Abstract Phosphorus (P) is a non-substitutable agricultural nutrient. Traditionally, agriculture was underpinned by natural processes leading to the release of phosphates which are available to crops, phosphate deposition from flooding and air, and often also by the recycling of organic residues. In parts of the world, these traditional P resources came to be viewed as a limiting factor to agricultural production in the nineteenth and early twentieth century. Feeding the current world population is dependent on these traditional P resources plus phosphate rock, which is the product of slow geological processes. Current practices are characterized by substantial P losses from agricultural soils, limited P use efficiency and limited recycling of organic residues to such soils. Continuation of such practices at current agricultural production levels will lead to a depletion of phosphate rock resources. Other potential P resources, such as P in steelmaking slags and landfills, seem relatively small if compared with phosphate rock resources. Phosphorus resources are limited but estimates regarding the timespan for depletion of phosphate rock resources vary much: between about 80 and about 1800 years at the current rate of mining. Phosphorus resources can be conserved by increased recycling of P to agricultural soils, reducing losses from agricultural soils and by improving the efficiency of P use in agriculture.