Soil Respiration across predominant Land-uses in the Vea catchment in the Sudan savannah zone, North-east Ghana

Abstract

A study to quantify soil respiration (SR) across predominant land-uses in the Vea catchment, a semi-arid Savannah ecosystem of Ghana, was carried out using the closed static chamber method and CO2 transmitter (GMD 20, Vaisala). The goal was to determine the magnitude of the contribution of soil CO2 flux from predominant land-uses to the global carbon budget. The annual soil CO2 fluxes determined from the predominant land-uses were related to the soil organic carbon (SOC) stocks under the land-uses. Additionally, the impact of cropping systems, field management practices, topography, soil temperature and moisture as well as their seasonal and spatial variability on soil CO2 fluxes were determined. The mean annual soil CO2 fluxes for the major land-uses, were significantly different (p=0.00); these were 12.79 ± 0.89, 9.10 ± 0.42 and 5.61 ± 0.29 t CO2 C ha-1 y-1 for woodland, graze-land and cropland respectively and these correlated strongly with SOC stock density of 37.91 ± 1.29 (woodland), 29.31 ± 1.74 (graze-land) and 27.36 ± 1.70 Mg C ha-1 (cropland). The overall mean annual soil CO2 flux from the catchment was 9.23 ± 0.53 t CO2 C ha-1 y-1. Carbon losses from land-use conversions of woodland to other land-uses were more pronounced in the cropland than in graze-land, which is poorly-managed native vegetation. Using the current (2013) SOC as the base year and assuming business as usual scenario, the IPCC SOC tool was used to estimate the decadal SOC dynamics of the land- uses for next 60 years. The mean soil CO2 flux under mixed cropping system was highest (114.67 ± 3.51) followed by rice monoculture (108.08 ± 2.82) whilst groundnut monoculture had the least (83.17 ± 2.85 [mgCO2 C m-2 h-1]). Fisher’s multiple tests revealed that mean soil CO2 fluxes were significantly different (p<0.05). The Soil CO2 fluxes were more sensitive to soil moisture stress than soil temperature at temperatures above 35 °C. Topography had significant impact on soil CO2 flux; lowland mean soil CO2 flux (86.3 [gCO2 C m-2month-1]) was over 30 percent higher than up-land mean soil CO2 flux (64.8 [gCO2 C m-2 month-1]) for all the land-uses and statistically, the CO2 fluxes were different (p<0.05) across the study field. There were marked seasonal and spatial variations in soil CO2 flux due to variations in local climate and soil attributes as influenced by the different land-uses. The mean C emission across the study field ranged between 8- 32 g m-2 week-1 depending on land-use type. The study concluded that land-uses and cropping systems, topography, porosity and soil moisture and temperature variations influence SR dynamics, SOC stocks and soil CO2 flux exchanges between land and atmosphere.