Extenders and Additives Nitrogen FOR FIELD CROPS

Nitrogen management continues to be diffi cult due to transformations of nitrogen fertilizers that are possible when applied to soil and the uncertainties of weather (Cabrera et al., 2008). Nitrogen (N) fertilizer in the form of urea is subject to ammonia volatilization through the activity of the urease enzyme found ubiquitously in soil (Kissel et al., 2008). Nitrate fertilizer is subject to leaching (Randall et al., 2008) or denitrifi cation (Coyne, 2008), depending on the water content of the soil and water movement through the soil. Ammonium forms of N can be fi xed (Kissel et al., 2008) or transformed to nitrate through the activities of specifi c soil bacteria (Norton, 2008). Because of these and other processes, nitrogen use effi ciency is low.