Constant, K. M. (1992). World nitrogen survey. World Bank.
Cita Chicago (17th ed.)Constant, Kurt Michael. World Nitrogen Survey. Washington, D.C: World Bank, 1992.
Cita MLA (9th ed.)Constant, Kurt Michael. World Nitrogen Survey. World Bank, 1992.
Atenció: Aquestes cites poden no estar 100% correctes.