AGRI-BRIEFS   AGRONOMIC NEWS ITEMS

From Agronomists of the Potash & Phosphate Institute 655 Engineering Drive, Suite 110 Norcross, Georgia 30092-2837 Phone (770) 447-0335

Spring 2001, No. 1

Producing and delivering fertilizers uses fossil fuel energy. Natural gas comprises 80 to 90 percent of the cost of producing ammonia. Phosphate production doesn’t use as much energy directly, but it depends on the petroleum industry for its supply of sulfur. It takes a ton of sulfur to produce a ton of P₂O₅. Potash mining uses little in the way of fossil fuel, but it requires energy to transport and apply any kind of fertilizer.

The raw materials for fertilizers are also non-renewable resources. While the supply of atmospheric nitrogen is virtually unlimited – about 37 thousand tons above every acre on the earth – it takes natural gas to make plant-available fertilizer from it. The estimated world reserves of phosphate rock amount to at least 3 billion tons of P₂O₅ – roughly 80 years’ supply at current rates of use. Known reserves of potash exceed 10 billion tons of K₂O – at least 400 years' supply.

But will North American reserves of phosphate rock run out within the next 25 years? Probably not. For both phosphate and potash, large resources that are uneconomical to mine with today’s technology and prices could potentially supply us into the future for 10 times as long as the known reserves. As recently as 1980 a publication forecast that Florida could run out of high-grade phosphate rock by the year 2000 – yet Florida today continues to supply most of North America’s demand. As with fossil fuels, new reserves continue to be discovered as fast as old ones are consumed.

Sustainability of fertilizer use also depends on its benefits to soil quality and health. Sustainable use recognizes that fertilizers boost the crop’s contribution of organic matter to the soil as well as its yield. Sustainable use aims to apply amounts in keeping with the needs of the cropping system, supplementing nutrients supplied by manures, crop residues, and other organic inputs. Sustainable use includes management that minimizes loss of nutrients to sensitive waters and the air, through knowledge of nutrient cycling.

The future will include more efficient capture of nutrients from animal manures, crop residues, and other organic materials. Agriculture will redesign itself to increase this efficiency, but some nutrients will continue to be lost to the larger cycles of nature. Nutrient demands will increase as yields continue to climb. Supplementing with fertilizers is a responsible use of natural resources from off the farm. Energy costs of transport and application are minimized when more concentrated nutrient sources are used.

No physical process is sustainable indefinitely. The key to sustainability is to use resources wisely to meet human needs for today and for future generations. Using mineral fertilizers to build soil health and to increase its capacity to produce food is a more sustainable investment than many others that are being made today.