With an increasing interest in closing the nutrient loop in agroecosystems, organic amendments are highly recommended as a reliable resource for soil nutrient recycling. However, from a carbon sequestration perspective, not much has been reported on the contribution of different organic amendments to soil organic carbon (SOC), crop carbon (C) uptake, and soil carbon dioxide (CO₂) emissions in wheat-maize cropping systems of sloppy upland soil. To fill the knowledge gap, a two-year lysimeter-field plots experiment was conducted in a sloppy upland purplish soil under wheat-maize cropping systems. The experiments were arranged in a complete random block design with five treatment plots, namely; fresh pig slurry as organic manure (OM), crop residues (CR), conventional mineral fertilizers (NPK) as the control, organic manure plus mineral fertilizers (OMNPK), and crop residues plus mineral fertilizers (CRNPK). Our results showed the leaf photosynthesis rate was not significantly increased by organic amendment application treatments compared to NPK treatment, and was within a range of 4.8 to 45.3 µmol m⁻² s⁻¹ for the wheat season and −20.1 to 40.4 µmol m⁻² s⁻¹ for the maize season across the five treatments and the measured growth stages. The soil CO₂ emissions for the maize season (in the range of 203 to 362 g C m⁻²) were higher than for the wheat season (in the range of 118 to 252 g C m⁻²) on average across the different experimental treatments over the two-year experiment. The organic amendment application increased annual cumulative CO₂ emissions from 30% to 51% compared to NPK treatment. Over the two years, the average crop C uptake ranged from 174 to 378 g C m⁻² and from 287 to 488 g C m⁻² for the wheat and maize seasons, respectively, and the organic amendment application increased the crop C uptake by 4% to 23% compared to NPK treatment. In the organic amendment treatments, the C balance ranged from −160 to 460 g C m⁻² and from −301 to 334 g C m⁻² for the wheat and the maize seasons, respectively, which were greater than those in the NPK treatment. Overall, the present study results suggest incorporation of organic amendments could be an effective strategy for increasing C sequestration and sustaining crop productivity in sloppy upland soil.

Vegetated drainage ditches (eco-ditches) have drawn much attention in recent years for the ability to remediate diffuse contaminants in rural wastewater through sediment retention, plant uptake and interception, and microbial metabolic activities. However, the effect of plant species on microbial community structure and nitrogen (N) retention in ditch sediment remains poorly understood. In this study, mesocosm plastic drums were planted with eight plant species commonly found in ditches and nurtured with wastewater for 150 days. Sediment total nitrogen (TN) was greatly increased after 150-day nurturing with rural wastewater, from 296.03 mg∙kg⁻¹ (Iris japonica Thunb) to 607.88 mg∙kg⁻¹ (Acorus gramineusO). This study also presents the effect of different plant species on sediment microbial communities, thus providing insight into N removal mechanisms in eco-ditch. Fifty-eight differentially abundant taxa were identified, and sediment microbial community structure for no plant (CK), Acg, Canna indica (Cai), and Typha latifolia L. (Tyl) was primarily linked to sediment NH₄⁺-N and TN. Extremely small proportions of ammonia oxidizing bacteria (AOB) and nitrifying bacteria were detected for all treatments, but large proportions of Crenarchaeota, which comprises the widely existent ammonium oxidized archaea (AOA), were found in CK, Acg and Cai. The abundance of Nitrosotalea from Crenarchaeota presented positive correlations with sediment NH₄⁺-N contents and ammonia oxidation function predicted by Faprotax, indicating Nitrosotalea might be the dominant ammonium-oxidizing microbes in sediment samples. The probable NH₄⁺-N removal pathway in wastewater sediment was through a combined effect of AOA, nitrifying bacteria, and anammox.

Soil acidification seriously threatens sustainable agriculture by promoting phytotoxic exchangeable aluminum ions (Al3+) accumulation and impairing crop growth. However, conventional soil amendments, such as lime and biochar, have known limitations, making the introduction of more sustainable soil amendments crucial for mitigating soil acidification. Furthermore, the biological and chemical mechanisms by which amendments alleviate acidification and enhance soil fertility remain unclear. This impedes the search for more cost-effective soil amendments to rehabilitate infertile acidic soils. In this study, pot experiments, microbial sequencing, and molecular modeling calculations were employed to assess the response of soil fertility and maize yield to the combined application of sodium carboxymethylcellulose (CMC) and desulfurized phosphogypsum (DP) in strongly acidic soils, as well as the underlying biological and molecular dynamic mechanisms. The results indicated that CMC + DP significantly reduced soil exchangeable Al3+ by 78.68–79.60%, while enhancing the base ion concentration by 59.93–102.27% and acid buffering capacity by 46.47–49.55% compared to the control (CK) in strongly acidic soils. Additionally, CMC + DP-amended soil exhibited a 24.47–48.65% increase in photosynthetic rate and a 50.57–155.48% increase in the weight of 100 grains. CMC contributed to Al3+ immobilization and base ion release via competitive electrostatic attraction and complexation of Al3+ on the surface of –COOH and –OH functional groups. CMC + DP application promoted direct enrichment of microbial communities, increasing the abundance of functional microbial taxa, including Acidobacteriota, Gemmatimonadota, and Ascomycota, and soil enzymes related to organic matter decomposition and phosphorus metabolism. These findings suggest that CMC + DP could be used as a promising strategy to mitigate soil acidification, enhance soil fertility and crop yield, and highlight the synergistic potential of biodegradable polymers and industrial by-products for acidic soil remediation. They enhance our understanding of the synergistic biological and molecular dynamic mechanisms of amendments, mitigating soil acidification and enhancing soil fertility. These findings may help identify more effective soil amendments and application strategies to ensure cropland health and promote sustainable agriculture.