Introduction

1. Introduction Materials and Methods NO3- NH4+ • Experiments were conducted in a Reed Canarygrass (Phalaris arundinaceae) field with Andisol, northeastern Japan (39o48'N, 141o05'E). • Cow slurry was splashed over the field on DOY 300 in 2004. • Closed chambers were placed 10m apart along a 150m-long transect in a slope (Photo 1). Gas samples were collected at 0, 15, and 30min. • Soil water content was measured with a 20cm-long TDR probe. • Surface soil samples were collected for chemical and d15N analyses (Fig. 1). • Photo 1. Closed chambers.Fig 1. d15N in NH4+ and NO3-. • The emission of greenhouse gases is a big concern. Agriculture is thought to be one of the largest sources of nitrous oxide (N2O). N2O is a by-product of both processes of nitrification and denitrification. Little information is available on which process is dominant in the field because most of such studies has been done in the laboratories. • We measured N2O gas flux after cow slurry application, and also measured NH4+- and NO3--N contents in soil and the natural abundance of nitrogen isotope (d15N). Fig. 4. N2O gas flux vs. NH4+ content and d15N-NH4+ in soil. Fig. 5. N2O gas flux vs. NO3-content and d15N-NO3- in soil. Acknowledgements This research was supported in part by the Grant-in-Aid for Scientific Research (B) (15380160) of JSPS. We are grateful to Mr. Muneaki Yokota for maintaining the grass field and his support to our research. References De Mello, W.Z., and M.E. Hines. 1994. Application of static and dynamic enclosure for determining dimethyl sulfide and carbonyl sulfide exchange in Sphagnum peatlands: Implications for the magnitude and direction of flux. J. Geophys. Res. 99:14601-14607. Nitrous oxide emission from dairy cow slurry applied to an Andisol grass field K. Noborio1, K. Ode2, C. Mizota3, N. Satta3, K. Koga3, and Y. Mukaida3 1 School of Agriculture, Meiji University, Kawasaki, Japan; 2 Utsunomiya University, Japan; 3 Iwate University, Japan Results Fig. 2. Finding parameters by fitting to N2O gas concentration. Fig. 3. Changes in air temperature and soil water content. • A large spike of N2O flux was observed on DOY 309, nine days after slurry application. • After the spike, the N2O flux was relatively steady with small fluctuations attributing to soil water content. • Increases in d15N of residual NH4+ and decreases in NH4+ content with steady NO3- content indicated the volatilization of NH4+ as NH3 gas. • Increases in d15N of both residual NH4+ and NO3- with increases in N2O flux indicated that N2O occurred both from nitrification and denitrification processes.