Effects of no-tillage and liming amendment combination on soil carbon and nitrogen mineralization

Although no-tillage (NT), as opposed to traditional tillage (TT), and lime application are both common practices to increase productivity of degraded soils, our understanding of their interactive effects on C and N cycling remains limited. Structural Equation Model (SEM) provides the opportunity to assess the direct and indirect effect of each agronomic practice on soil biogeochemical processes and determine the causal links among studied variables. We investigated the causal relationships among soil chemical and biological properties and C and N mineralization rates as affected by tillage practices (NT versus TT) and liming amendment (sugar foam plus red gypsum versus no amendment) using SEM. The adoption of NT increased soil C content (38.3 and 33.7 g C kg(-1) in NT and TT, respectively), microbial activity and C mineralization in the topsoil, while amendment increased soil pH from 4.25 to 5.49 pH units and accelerated the N cycling. The SEM revealed that C mineralization was only affected by tillage practices while net N mineralization (NNM) was increased by NT adoption and liming amendment. The absence of relevant effects of amendment on C mineralization indicated that there is no C depletion risk. However, these results suggest a possible decoupling between the C and N mineralization processes with potential implications for N losses. In addition, SEM revealed that the impact of tillage practice on C and N mineralization was mediated by changes in the microbial biomass, which highlights the importance of the inclusions of microbial parameters in the nutrient cycling studies as affected by agronomic practices. In conclusion, the combination of NT and liming amendment increased soil C content, and stimulated N cycling, which could enhance N availability N for crops or increase N losses. This study showed the usefulness of SEM in agronomic experiments, which could help in the future to improve agronomic management and enhance sustainable use of agricultural land.