Effects of land management on CO2 flux and soil C stock in two Tanzanian croplands with contrasting soil texture

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.

► Estimated CO2 flux in Control plot was 0.9–2.2 Mg C ha−1 yr−1 in both soil textures.
► Plant residue application increased the CO2 flux by ∼100% in each site.
► Plant residue application also increased soil C stock by ∼15% in each texture.
► Efficiency of C accumulation was 7.6% in sandy soil, though was 14.6% in clayey soil.
► Our results indicate that dry tropical croplands may be used as a C sink.