Effects of single and mixed plant types on soil carbon and nitrogen dynamics in homestead agroforestry systems in Northern Bangladesh

Abstract

The importance of plant types and diversity have been focused for studying aboveground nutrients dynamics in the agroforestry system; however, a substantial knowledge gap remains for the belowground nutrients. We tested the effects of plant types (shrub vs. tree vs. tree-shrub) and diversity indices on soil organic carbon (SOC) and soil nitrogen (SN) dynamics in 64 homesteads in northern Bangladesh. We found that SOC, SN and soil C:N ratio were higher in the mixed plant types (tree-shrub) homesteads than single plant types (tree or shrub) homesteads. Both SOC and SN were higher in 0–10 cm than 10–20 cm soil depth in shrub homesteads (SOC: P = 0.011; SN: P = 0.023), and tree-shrub homesteads (SN: P = 0.03). In contrast, C:N ratio was consistently higher in 10–20 cm soil depth (P < 0.05) but no differences were found in bulk density (BD) (P > 0.05) across homesteads. Shannon diversity, Simpson richness and plant density positively related with SOC and SN. High plant diversity and density promoted SOC and SN more in tree-shrub homesteads than in shrub and tree homesteads, while none of the relationships differ between shrub or tree homesteads. These results indicate that mixture of plant types and their diversity elevate SOC and SN contents in homesteads. Hence, the integration of both tree and shrub under homestead agroforestry system have great potential for SOC and SN storage in the study sites and areas in other subtropical countries with substantial homestead coverage.