Understanding the Priming Effect and the Routes and Stocks of C in Incubated Soil with Residue Inputs

Abstract

The priming effect is a strong short-term change of organic matter decomposition that can accelerate or slow residue decomposition, and release or immobilize a large amount of carbon (C) and nitrogen (N) in soil. Our goal here was to (i) monitor the influence of residue additions in stocks of C and N in residues and soil (ii) and identify the main routes of C stabilization and the priming effect in soil. An incubation study was run with residue additions of high C:N (brachiaria and sugarcane) and low C:N (soybean) in soil. CO2 emissions, stocks of C (humic substance; labile C and C mic) and N (soil and residues) were monitored for 50 days, and the priming effect and route of C were calculated. Results showed that after incubation the final stocks of humin increased (31%), while there were reductions of humic (54%) and fulvic acids (42%). The stocks of soil total C and N were constant, while the residue C was decreased. The residues with high C:N immobilized N, while there was a decrease of N in residues with low C:N. There was a positive priming effect and a C stabilization route concentrated from C mic to humic substances with the addition of low C:N, while inputs of high C:N diversified the C stabilization routes from C mic or labile C to humic substances. The C routes were intense because the study was run in control conditions with a loam soil and adequate conditions of water, oxygen, and temperature.