Carbon dioxide flux and soil carbon stock as affected by crop residue management and soil texture in semi-arid maize croplands in Tanzania

Crop residue management strategies must be adapted for improving carbon (C) balance and soil C stock in agroecosystems in sub-Saharan Africa with consideration of the crop residue availability and site-specific soil characteristics. We conducted field experiments to determine the effects of crop residue application method (incorporation/mulching) and quality (maize/cowpea) and N fertilizer application on the soil respiration rate and soil C stock in the surface soil layer (0-15 cm) in maize croplands with contrasting soil textures (clay/sandy) over 2 years from 2012 to 2014 in Tanzania. At the clay site, the incorporation of maize residues showed a 38% increase in CO2 flux compared to mulching, whereas, at the sandy site, mulching showed a 16% increase compared to the incorporation. At the sandy site, mulching practice retained soil moisture content and apparently enhanced the decomposition of the original soil organic C in the surface layer. It is, therefore, suggested that mulching practice may accelerate a long-term depletion of soil C stock at the sandy site. The cowpea residue incorporation led to rapid decomposition because of its high biodegradability at both sites. The N fertilizer application stimulated the decomposition of labile soil organic matter. The soil C stock in the surface layer did not significantly change after the 2-year experiment, irrespective of crop residue treatment and soil type. In conclusion, adequate crop residue management in terms of suppressing CO2 flux during a cropping season depends on soil type, but the long-term effect on soil C stock is unclear.

Automated summary

Crop residue management strategies need to be adapted for improving carbon balance and soil carbon stock in sub-Saharan Africa. In a 2-year field experiment in Tanzania, the effects of crop residue application methods and quality on soil respiration rate and carbon stock were studied, showing that mulching practice in sandy soils increased soil moisture, enhanced organic carbon decomposition, and may lead to long-term depletion of soil carbon stock.