Incorporating crop residues into the soil is an effective method for improving soil carbon sequestration, fertility, and crop productivity. Such potential benefits, however, may be offset if residue addition leads to a substantial increase in soil greenhouse gas (GHG) emissions. This study aimed to quantify the effect of different crop residues with varying C/N ratios and different nitrogen (N) fertilizers on GHG emissions, yield, and yield-scaled emissions (GHGI) in winter wheat. The field experiment was conducted during the 2018–2019 winter wheat season, comprising of four residue treatments (no residue, maize residue, soybean residue, and maize-soybean mixed residue) and four fertilizer treatments (control, urea, manure, and manure + urea). The experiment followed a randomized split-plot design, with N treatments as the main plot factor and crop residue treatments as the sub-plot factor. Except for the control, all N treatments received 150 kg N ha⁻¹ season⁻¹. The results showed that soils from all treatments acted as a net source of N₂O and CO₂ fluxes but as a net sink of CH₄ fluxes. Soybean residue significantly increased soil N₂O emissions, while mixed residue had the lowest N₂O emissions among the three residues. However, all residue amendments significantly increased soil CO₂ emissions. Furthermore, soybean and mixed residues significantly increased grain yield by 24% and 21%, respectively, compared to no residue amendment. Both soybean and mixed residues reduced GHGI by 25% compared to maize residue. Additionally, the urea and manure + urea treatments exhibited higher N₂O emissions among the N treatments, but they contributed to significantly higher grain yields and resulted in lower GHGI. Moreover, crop residue incorporation significantly altered soil N dynamics. In soybean residue-amended soil, both NH₄⁺ and NO₃⁻ concentrations were significantly higher (p < 0.05). Conversely, soil NO₃⁻ content was notably lower in the maize-soybean mixed residue amendment. Overall, our findings contribute to a comprehensive understanding of how different residue additions from different cropping systems influence soil N dynamics and GHG emissions, offering valuable insights into effective agroecosystems management for long-term food security and soil sustainability while mitigating GHG emissions.

The application of mineral fertilizers can effectively enhance crop yields. However, this potential benefit may be diminished if the use of mineral fertilizers leads to a substantial decline in soil organic carbon (SOC) and an increase in soil greenhouse gas (GHG) emissions. This study aimed to determine the optimal fertilizer combinations and rates for improving SOC and maize yield while reducing GHG emissions in the semi-arid uplands of Kenya. Data were collected from five different fertilizer treatments (N50, N100, N150, N100+manure, and N100+straw) compared to a control (N0) in a long-term experimental field, which was used to run and validate the DNDC model before using it for long-term predictions. The results showed that the combination of mineral fertilizer and straw resulted in the highest SOC balance, followed by that of fertilizer and manure. All fertilized treatments had higher maize grain yields compared to low-fertilizer treatment (N50) and control (N0). Daily CO₂ fluxes were highest in the treatment combining mineral fertilizer and manure, whereas there were no significant differences in N₂O fluxes among the three tested treatments. The findings of this study indicate that the judicious application of mineral fertilizer, animal manure, and straw has great potential in enhancing SOC and maize yields while reducing GHG emissions, thereby providing practical farming management strategies in semi-arid Kenya.

Bioethanol production from cereal straw is a sustainable alternative to meet the current energy demand, but its low nitrogen (N) content and high carbon to nitrogen (C/N) ratio are problematic during bioethanol processing. Intercropping cereals with legumes may increase the N content and reduce the C/N ratio in the harvested straw biomass. In order to investigate the combined production of food, feed, and suitable feedstock (low C/N ratio) for lignocellulosic bioethanol production, a field experiment on cereal-legume intercropping was carried out in southern Sweden. In the experiment, autumn-sown cereals (wheat, triticale, and rye) were grown as monocrops with two different N fertilization levels (60 and 120 kg N ha⁻¹) or intercropped with autumn-sown or spring-sown (undersown) clover-grass, autumn-sown or spring-sown (undersown) alfalfa, or autumn-sown faba bean. Total grain dry matter yield, cereal grain protein content, straw dry matter yield, and straw biomass C/N ratio were estimated. The results showed that the intercrops produced more straw biomass and had a lower C/N ratio, but produced less grain, than cereal monocrops. Among the cereals, rye showed significantly higher grain and straw yields, but lower grain protein content, in all treatments. Among the intercrop treatments, cereal with spring-sown clover-grass produced higher grain and straw yields and had a significantly lower C/N ratio (38:1) than the other treatments. Thus, cereal with spring-sown (undersown) clover-grass is a promising cropping system for lignocellulosic bioethanol production.