Carbon and nitrogen dynamics in a successional agroforestry system in the Neotropics

The present study aimed to assess the effect of fourteen years of implementation of a successional and biodiverse agroforestry system (AFS) in a degraded agricultural field located in the Cerrado region of Central Brazil on the carbon and nitrogen dynamics. To track short term soil N dynamics we sampled instantaneous soil N rates in four seasonal periods (wet-dry, dry, dry-wet, wet) and to track long term C and N dynamics we measured C and N stable isotopes in the plant-litter-soil system. As additional data we determined the aboveground biomass; resorption rates of foliar and, soil C and N stocks.  The measured aboveground biomass was 19.2 Mg C ha-1. The mean resorption rate of foliar N was 49.3%. C:N ratio was 20.4 ± 1.4 and 14.2 ± 0.32 in the litter layer and the topsoil, respectively. Soil N-NH4+ was predominant over N-NO3-. After 40 days, the cumulative N-N2O emission was 0.33 kg ha-1. The mean C and N stocks were 3.8 Mg N ha-1 and 43.6 Mg C ha-1, respectively. The averaged soil δ15N was 6.8‰. Soil δ13C was -20.3‰. After 14 years of implementation, approximately 40% of the total C in the topsoil (0-20 cm depth) was derived from the AFS biomass input, predominantly from the C3 photosynthetic pathway. The studied biodiverse AFS that replaced a degraded agricultural field in the Cerrado region showed to be responsive both in terms of soil and plant C and N pools and fluxes.