Natural gas is the primary input to ammonia production, which, in turn, is the major input to production of nitrogen fertilizer. In recent years, increasing demand for natural gas and variations in supply have caused shortrun fluctuations in natural gas prices, affecting nitrogen fertilizer production costs and prices. Phosphate and potash fertilizers are mined, with prices reflecting increased mining costs and annual variations in demand. The long-term upward trends in natural gas and fertilizer prices are expected to continue as production costs increase.