Carbon and nitrogen mineralization during decomposition of crop residues in a calcareous soil

The present work was aimed at evaluating, under laboratory conditions, the medium-term influence of pepper residues applied at different rates (2,3 and 5 g kg(-1)) on carbon and nitrogen cycles in an agricultural soil. The cumulative quantities of CO2-C that evolved from the pepper residue mineralization were fitted to a first-order kinetic model. These values are equivalent to similar to 30% of the organic carbon added for all doses, with similar mineralization constant rate (similar to 0.09 days(-1)). Net ammonification followed the same pattern in all doses indicating a net loss of NH4+-N by nitrification or immobilization. Net nitrification followed a different pattern depending on the dose. Final positive values were observed for the two highest doses, but when 2 g kg(-1) was applied, net nitrification was always negative, suggesting net immobilization of N. The net N mineralization was -3.1, 13.7 and 56.7 mg kg(-1) for doses 2,3 and 5 g kg(-1), respectively. Thus, the addition of pepper residues at low doses produced a net N immobilization in soil. This trend may indicate that N is likely a limiting factor for microbial growth. The activities of soil enzymes involved in C and N cycles responded differently according to the dose, indicating that only the highest dose would increase the capacity of soil to perform useful ecosystem functions. These results highlight the importance of dose when applying pepper residues, since doses <5 g kg(-1) do not easily release available N for plant growth in the loamy calcareous soil used for this experiment. (C) 2014 Elsevier B.V. All rights reserved.