CARBON AND NITROGEN BUDGETS OF 4 AGROECOSYSTEMS WITH ANNUAL AND PERENNIAL CROPS, WITH AND WITHOUT N-FERTILIZATION

Annual carbon and nitrogen budgets were calculated for barley Hordeum vulgare without N fertilizer (B0), barley fertilized with 120 kg N ha-1 yr-1 (B120), a meadow fescue Festuca pratensis ley with 200 kg N ha-1 yr-1 (GL), and a lucerne Medicago sativa ley (LL) capable of fixing nitrogen. Net annual primary production was 260, 480, 740 and 790 g C m-2 in B0, B120, GL and LL, respectively. Annual inputs of organic carbon to the soil were less different between crops; 150-180 g C m-2 in barley and 260-270 g C m-2 in the leys. Total annual soil respiration, 230 g C m-2 in barley and 350-400 g C m-2 in the leys, closely matched the input of C to decomposer organisms plus C respired by roots. Both leys accumulated C, mainly as increases in plant standing crop. Total inputs and outputs of N were roughly balanced in the fertilized barley, while total n in the unfertilized barley declined by 4 g m-2 yr-1. Total N increased in the N-fixing lucerne ley, with a net increase in plant standing crop of 9 g N m-2 yr-1 and in soil N of 3 g N m-2 yr-1. The grass ley showed a net change in total N of -5 g m-2 yr-1. Net nitrogen mineralization ranged between 8 g m-2 yr-1 in B0 and 21 g m-2 yr-1 in GL, and corresponded to c1% of total soil N in barley and 2% of total soil N in the leys. The grass ley considerably enhanced net mineralization of soil organic matter N. Total losses of nitrogen due to leaching and gaseous emissions ranged between 1 g N m-2 yr-1 in B0 and GL to 2 g m-2 yr-1 in LL. Denitrification rates were lowest in barley, but both unfertilized and fertilized barley leached more N than the leys. There were no large differences in microbial biomass between treatments but microbial production was 50% higher in the leys than in the barley treatments. This pattern corresponded to that of soil meso- and macrofauna biomass and total faunal consumption and respiration, where B0 < B120 < GL < LL. -from Authors