Carbon and nitrogen budgets of four agro-ecosystems with annual and perennial crops, with and without N fertilization.
In field trials at Kjettslinge near Uppsala in 1980-85, annual C and N budgets were calculated for the following systems: (a) barley without fertilizer; (b) barley + 120 kg N fertilizer/ha per year; (c) Festuca pratensis + 200 kg N; (d) Medicago sativa ley without applied N. Annual net primary production (including rhizodeposition) was 240, 480, 740 and 790 g C/m2 in (a), (b), (c) and (d), resp., and annual organic C inputs to the soil were 150-180 g C/m2 in (a) and (b) and 350-400 g C in the leys. Total annual soil respiration was 230 g C in (a) and (b) and 350-400 g C in (c) and (d) and closely matched C input to decomposer organisms and C respired by roots. C accumulated in (c) and (d) mainly as increases in plant standing crop. Total N inputs and outputs balanced in (b) but decreased by 4 g/m2 per year in (a). Total annual net increased in (c) by 9 g in plant standing crop and 3 g in soil. Net N mineralization corresponded to 1% of total soil N in barley and 2% in leys. Denitrification rates were lowest and leaching losses were highest in barley. Estimated microbial production was 50% higher in the leys than in the barley systems.