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Evaluation of carbon dynamics is of great concern worldwide in terms of climate change and soil fertility. However, the annual CO₂ flux and the effect of land management on the carbon budget are poorly understood in Sub-Saharan Africa, owing to the relative dearth of data for in situ CO₂ fluxes. Here, we evaluated seasonal variations in CO₂ efflux rate with hourly climate data in two dry tropical croplands in Tanzania at two sites with contrasting soil textures, viz. clayey or sandy, over four consecutive crop-cultivation periods of 40 months. We then: (1) estimated the annual CO₂ flux, and (2) evaluated the effect of land management (control plot, plant residue treatment plot, fertilizer treatment plot, and plant residue and fertilizer treatment plot) on the CO₂ flux and soil carbon stock at both sites. Estimated annual CO₂ fluxes were 1.0–2.2 and 0.9–1.9 Mg C ha⁻¹ yr⁻¹ for the clayey and sandy sites, respectively. At the end of the experiment, crop cultivation had decreased the surface soil carbon stocks by 2.4 and 3.0 Mg C ha⁻¹ (soil depth 0–15 cm) at the clayey and sandy sites, respectively. On the other hand, plant residue application (7.5 Mg C ha⁻¹ yr⁻¹) significantly increased the surface soil carbon stocks, i.e., 3.5–3.8 and 1.7–2.1 Mg C ha⁻¹ (soil depth 0–15 cm) at the clayey and sandy sites, respectively, while it also increased the annual CO₂ fluxes substantially, i.e., 2.5–4.0 and 2.4–3.4 Mg C ha⁻¹ yr⁻¹ for the clayey and sandy soils, respectively. Our results indicate that these dry tropical croplands at least may act as a carbon sink, though the efficiency of carbon accumulation was substantially lower in sandy soil (6.8–8.4%) compared to clayey soil (14.0–15.2%), possibly owing to higher carbon loss by leaching and macro-faunal activity.
