N2O EMISSION FROM ENERGY CROP FIELDS OF MISCANTHUS GIGANTEUS AND WINTER RYE

The emission of the greenhouse gas nitrous oxide (N2O) from energy cro p fields lower the reduction of the greenhouse effect achieved by the substitution of fossil fuels by energy crops. For that reason N2O flux es were measured during the cropping season in Miscanthus ''Giganteus' ' (M. ''Giganteus'') plots with and without N fertiliser addition and in fertilised winter rye (Secale cereale) plots by using a closed-cham ber technique, able to contain the growing plants. The highest N2O emi ssion from the M. ''Giganteus'' soil occurred after fertilisation in s pring with 75 kg NH4NO3-N ha(-1), whereas the rye soil showed no N2O e mission response at fertilisation with 120 kg NH4NO3-N ha(-1). The unf ertilised M. ''Giganteus'' soil and the rye soil both showed similar s mall N2O emissions. The largest proportion of the annual N2O emission occurred in the summer for the fertilised M. ''Giganteus'' and in autu mn for fertilised winter rye. The average N2O flux during 207 days was 109 mg N2O-N m(-2) from the fertilised M. ''Giganteus'' soil, which w as twice the amount emitted from the rye soil. The N2O emissions from the soils were equivalent to 1.5 and 0.5% of the fertiliser applied to M. ''Giganteus'' and rye, respectively, corresponding to 136 and 36 m g N2O-N (kg dry matter)(-1). The precipitation was low and therefore t he measured N2O fluxes may have been lower than expected of an average year. Still, the results suggest that the N2O emission from a sandy l oam cropped with rye or M. ''Giganteus'' is a minor problem in the use of energy crops for reducing of the greenhouse effect. (C) 1997 Elsev ier Science Ltd.