Nitrogen cycling in conventional and no-tillage agro-ecosystems: analysis of pathways and processes.
Sorghum cv. Funk's 522 was grown in 1978 followed by rye cv. Abruzzi under conventional tillage (CT) (disc ploughing) or no tillage (NT). Soyabean cv. Bragg sown in 1980 and followed by rye cv. Abruzzi was also grown under conventional tillage (mouldboard and disc ploughing) or no tillage. Crop biomass, aboveground weed biomass and litter were sampled fortnightly for the first 2 months and then at 4-week intervals. N fixation by soyabeans was determined twice in 1980. Changes in crop biomass, weed biomass, and surface litter during 1978-81 were similar for both CT and NT, although weed biomass was higher in NT. Seasonal changes in shoot:root ratios for total biomass, percentage N content and total N content occurred in parallel for CT and NT. Crop N content on an area basis was higher for CT on several occasions while percentage N content of soyabean foliage was also higher in CT systems. Annual N budgets for CT and NT sorghum/rye and soyabean/rye agro-ecosystems suggested that N cycling processes showed some similarity in both CT and NT, with a trend of increasing divergence. N fluxes between component pairs were increased by ploughing. Grain yields were unaffected by tillage practices. It was concluded that soil tillage practices provide some regulation of N fluxes and N storage capacity within ecosystems. The undisturbed soil and litter layers of NT systems generated decomposition processes similar to those in natural terrestrial ecosystems.