Building Up Organic Matter in a Subtropical Paleudult under Legume Cover‐Crop‐Based Rotations

Abstract

The potential of conservation management systems to ameliorate degraded agricultural soils and mitigate global warming is related to their potential for long‐term stabilization of soil organic matter (SOM). This study was performed in a 19‐yr‐old experiment that was set up on a degraded Paleudult (220 g kg −1 clay) in southern Brazil to (i) evaluate the effect of seven no‐till crop rotations (grass‐ and legume‐based cover crop systems) and mineral N fertilization (0 and 145 kg ha −1 yr −1 ) on soil organic C (SOC) stocks (0–17.5‐cm depth) and (ii) estimate rates of SOM dynamics in these systems under subtropical climate conditions. Annual C input (shoot + root) ranged from 2.61 to 7.84 Mg ha −1 , with the highest values in legume‐based and N‐fertilized cropping systems. The SOC stocks were closely related to C input levels, and a minimum C input of 4.05 Mg ha −1 yr −1 was estimated to maintain the original SOC stock of 31.38 Mg ha −1 Based on the one‐compartment model of SOM dynamics, the SOM decomposition rate was estimated to be 1.2% and the humification coefficient was estimated to be 9.6%. After 19 yr, the stock of the original SOC decreased to about 24.78 Mg ha −1 , while accumulation of SOC derived from the crops ranged from 4.26 to 12.79 Mg ha −1 Our results highlighted the benefits of legume cover crop species in no‐till systems for the stabilization of SOC in degraded agricultural soils.