Soil nitrogen dynamics under different quality and application methods of crop residues in maize croplands with contrasting soil textures in Tanzania
Nishigaki, Tomohiro | Sugihara, Soh | Kilasara, Method | Funakawa, Shinya
Soil nitrogen (N) dynamics in croplands need to be improved for the increase of food production in sub-Saharan Africa. Our objective was to investigate the crop residue management in terms of quality and application method to improve soil N dynamics during the period of crop growth in maize croplands with special reference to soil textures in dry tropical agroecosystems. Field experiments were conducted during the rainy seasons of 2012 and 2013 at clayey and sandy sites in Tanzania. Five treatment plots were established: plots with no residue applied (Ctrl plot), chemical fertilizer applied (F plot), maize residue (high C:N ratio = 60) incorporated (M-In plot) or mulched (M-On plot), and cowpea residue (low C:N ratio = 21) incorporated (P-In plot). In each plot, we regularly collected surface soil and crop samples and measured inorganic N (NO ₃⁻–N and NH ₄⁺–N), the soil respiration rate, and crop N uptake. Rainfall and soil moisture content were also continuously monitored. Our results showed that cowpea residue with high biodegradability caused prompt increases in the soil respiration rate and soil inorganic N because decomposition of the applied residue occurred within ca. 2 weeks after the application at both the clayey and sandy sites. It resulted in high N use efficiency in the early growing period and 18–73% higher total crop N uptake than that in the maize residue plots at both sites. The application methods (incorporation and mulching) showed no significant difference in soil N dynamics and crop yield, although higher soil respiration was observed in the M-In plot than the M-On plot at the clayey site. However, at the sandy site, mulching of maize residue resulted in the increased soil inorganic N content in the M-On plot by 18–26% compared with that in the M-In plot during the cropping season because of the higher soil moisture content. Consequently, crop N uptake in the mulching plot resulted in 26–59% higher than that in the incorporation plot.
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