MITIGATION ALTERNATIVES TO DECREASE NITROUS OXIDES EMISSIONS AND UREA-NITROGEN LOSS AND THEIR EFFECT ON METHANE FLUX

Nitrous oxide (N2O) and methane (CH4) are greenhouse gases that are co ntributing to global warming potential. Nitrogen (N) fertilizer is one of the most important sources of anthropogenic N2O emissions. A field study was conducted to compare N-use efficiency and effect on N2O and CH4 flux, of urea, urea plus the nitrification inhibitor dicyandiamid e (U + DCD), and a control release fertilizer, polyolefin coated urea (POCU) in irrigated spring barley (Hordeum vulgare L.) in northeastern Colorado. Each treatment received 90 kg urea-N ha(-1) and microplots labeled with N-15-fertilizer were established. Average N2O emissions w ere 4.5, 5.2, 6.9, and 8.2 g N ha(-1) d(-1) for control, U + DCD, POCU , and urea, respectively. During the initial 21 d after fertilization, N2O emissions were reduced by 82 and 71% in the U + DCD and POCU trea tments, respectively, but continued release of N fertilizer from POCU maintained higher N2O emissions through the remainder of the growing s eason. No treatment effect on CH4 oxidation in soils was observed. Fer tilizer N-15 found 50 to 110 cm below the soil surface was lower in th e POCU and U + DCD treatments. At harvest, recovery of N-15-fertilizer in the plant-soil system was 98, 90, and 85% from POCU, urea, and U DCD, respectively. Grain yield was 2.2, 2.5, and 2.7 Mg ha(-1) for PO CU, urea, and U + DCD, respectively. Dicyandiamide and POCU showed the potential to be used as mitigation alternatives to decrease N2O emiss ions from N fertilizer and movement of N out of the root zone, but N r elease from POCU does need to be formulated to better match crop growt h demands.