Soil nitrogen dynamics under different quality and application methods of crop residues in maize croplands with contrasting soil textures in Tanzania

Abstract

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.

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

“…Presumably, the soil respiration observed in the M‐On plot was derived more through the decomposition of the original soil organic matter (SOM), which generally has a narrow C:N ratio compared to maize residue (Table 1). This is corroborated by our previous study, in which there was a larger increase in soil inorganic N in the surface layer of the M‐On plot than the M‐In plot (Nishigaki et al., 2017). In terms of conservation agriculture in tropical semi‐arid sandy soils, this finding indicates that surface crop residue application can increase the availability of soil moisture, subsequently increasing inorganic N in the surface layer, whereas it might reduce soil fertility through the depletion of labile SOM stock on a long‐term scale.…”

“…The estimated decomposition of maize ranged 15%–33% of the applied residue, which was consistent with our previous study conducted at the same sites (22%–26%) (Sugihara et al., 2012). In addition to the leftover residues, the C input from the root biomass grown in the cropping seasons, although not measured in this study, was estimated to be 1.2 Mg C ha −1 over the 2‐year experiment based on above‐ground biomass and root‐to‐shoot ratio (Nishigaki et al., 2017; Turan et al., 2010). Considering the possibility of high input from leftover residues and belowground biomass, the C balance in maize residue‐applied plots (M‐In and M‐On plots) was lower than expected from the calculation.…”

Effect of Soil Tillage and Crop Sequence on Grain Yield and Quality of Durum Wheat in Mediterranean Areas

“…Besides, fertilization strategies [18] as well as soil management, cover crops, and crop rotation are fundamental variables that affect physiological traits, and consequently, the quality (protein profile) and yields [19]. Crop rotation and residues influence carbon and N dynamics in soil [20], especially in low organic matter and N environments (i.e., Mediterranean areas); crop residues on soil surface are, indeed, not only mere soil protectors from erosion, but affect nutrient and water availability that in turn increase and stabilize yields [21][22][23][24][25].…”