Vertical distribution of soil properties and organic carbon under different land use systems in saline soils of Bangladesh

This study has been conducted to investigate the impact on different land-use on soil organic carbon stock and selected soil properties in soil profiles; along with a preponderance of SOC into different pools of oxidizability with depth increment; under different land-use systems in saline soil and to screen out which land practices are best for soil carbon storage. Soil samples were collected at 0–15, 15–30, 30–45, 45–60, 60–75, 75–90, and >90 cm depths by the opening pit in three different locations under different cropping patterns (Rice-vegetable, Rice-fallow, and Rice-shrimp) with three replicates, then analyzed. Results showed that the SOC content and SOC stock significantly (p ≤ 0.05) increased with depth increments in Rice-vegetables land-use system while it decreased with depth in the Rice-fallow system. At the greater depth of >90 cm, SOC stock has been found highest which is true for both Rice-vegetables (3375 t C/ha) and the Rice-shrimp system (2268 t C/ha). But the greater depth of the Rice-fallow system contains the least amount (296.4 t C/ha). Also, textural analysis of soil showed that the soils from each cropping system were dominant in silt particles. It is found that both clay and silt particles had accumulated at a lower depth in all of the cropping systems which was also significant (p ≤ 0.05) along soil profile may be due to the puddling and tillage operations for rice cultivation. Higher content of CaCO3 was obtained under both Rice-vegetable and Rice-fallow land-use systems (5.19%) at 75–90 cm and 60-75 cm depth, respectively which may be attributed to the process of calcium leaching and subsequently precipitated as CaCO3 at a lower profile. An increase in depth, active pools of carbon decreased significantly (p ≤ 0.05) in Rice-vegetables, Rice-shrimp and Rice-fallow land-use system till from 30 to 45 cm, 30 to 90 cm, and 45 to 90 cm respectively which is an early indicator of soil quality. The highest (5.1 g C/kg) and lowest (0.2 g C/kg) amount of very labile fraction was obtained under Rice-vegetable and Rice-shrimp system at 75–90 cm and 0–15 cm depth, respectively. By contrast, passive pools of carbon and its recalcitrant nature increased significantly (p ≤ 0.05) with depth for Rice-vegetable and Rice-shrimp land-use systems.