TY - JOUR T1 - Quantifying the loss mechanisms of nitrogen JF - Journal of Soil and Water Conservation SP - 389 LP - 398 VL - 57 IS - 6 AU - J. A. Delgado Y1 - 2002/11/01 UR - http://www.jswconline.org/content/57/6/389.abstract N2 - Nitrogen (N) is a key factor in maintaining higher yield production and worldwide economic viability of agricultural systems. Since N is one of the most dynamic and mobile elements, its management is difficult, especially in irrigated systems where significant losses can be produced by leaching or denitrification. The major pathways for N loss are ammonia (NH3) volatilization; emissions of nitrous oxide (N2O), oxides of N (NO and NO2), and dinitrogen (N2) gases; leaching of nitrates (NO3); and off-site transport due to wind and water erosion of N tied in the organic matter and in the inorganic NO3 and ammonium (NH4) compartments. Nitrogen is dynamic and mobile. Its fate and transport in agricultural systems is affected by management and unpredictable events. Its average worldwide N use efficiencies (NUEs) have been reported to be about 50% and even as low as 33% for cereals. Farmers usually apply a uniform rate of N to agricultural fields assuming that N sources, sinks, and mechanisms for loss are constant across fields. It is well documented that variability of soil properties that affect N sources makes managing N to maximize NUE difficult. Such variable soil properties include soil organic matter content, residual soil NO3-N, amount of crop residue returned to the surface soil, yield variability (N sink), and changes in soil chemical and physical properties. Fields vary from coarse gravelly areas where N losses are primarily attributed to NO3-leaching, to clayey areas where water is ponded and N losses may be primarily dominated by denitrification (N2/N2O). Management is being established as the predominant factor that can reduce N losses in the environment. If we are to improve N management to increase NUE we will need to do it within the context of the N cycle accounting for N loss mechanisms and how to manage them. This paper will review how we can quantify these N losses. ER -