Affiliations: Laboratory of Terrestrial Ecological Process,
Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016,
China. Email: gxchen @ iae. syb. ac. cn
Abstract: Laboratory and in situ experiments were done to investigate the
influences of cultivation on temperate semi-arid grassland (for 17years spring
wheat planted once every two years without fertilization) on soil N_2O emission
and quantitative variations of related soil microbes.In the laboratory
(25°C and soil moisture 18% ), cultivation increased soil transformations
of fertilizer nitrogen ( 100 µg N/g as NaNO_3, urea,or as urea with
dicyandiamide 1 µg N/g). The N_2O emissions from the cultivated and
uncultivated soils with or without nitrogen additions were relatively low, and
mainly originated from the nitrification. The soil N_2O emission due to
cultivation decreased somewhat upon no fertilization or NaNO_3 addition, but
significantly upon urea addition. The role of dicyandiamide as nitrification
inhibitor was only considerable in the cultivated soil, and had small influence
on decreasing N_2O emission in the two soils. The influence of cultivation on
soil N_2O emission was also reflected by the number variations of microbes
related with soil nitrogen transformation in the two soils. Compared to the
uncultivated grassland, in situ ammonifiem and denitrifiers in the cultivated
grassland quantitatively averagely increased, and aerobic no-symbiotic
azotobacters were quantitatively similar, leading to the continued decrease of
organic matter content and the decrease of N_2O emission from the cultivated
grassland soil.