Soil organic carbon (SOC), the largest terrestrial organic carbon stored on land, plays a crucial role in regulating climate via soil carbon sequestration. Soil carbon sequestration, also known as “carbon farming” or “regenerative agriculture,” refers to various practices that manage land, especially farmland, to increase the amount of carbon stored in soils. In the soil, SOC acts as a major carbon sink by absorbing and storing atmospheric CO₂. Approximately 1,550 gigatons of organic carbon are stored in soils, accounting for about 73% of the estimated 2,110 gigatons of organic carbon in the biosphere. Also a vital component of land ecosystems, it significantly influences soil fertility, structure, and overall ecosystem health. Carbon sequestration can affect the mitigation of climate change, soil health and productivity, food security, and ecosystem services. The dynamics of SOC are regulated by the balance between inputs, including plant residues, root exudates, and microbial activity, and outputs, such as decomposition and mineralization processes These processes are governed by physical, chemical, and biological mechanisms. It also affected agricultural management like conservation tillage, crop rotation, cover crops, organic amendments (manure, compost, and biochar), and agroforestry systems. Measuring SOC is challenging due to factors like spatial variability, temporal variation, and sampling depth. Therefore, using modeling to understand and quantify soil carbon sequestration is vital for sustaining agricultural systems and directing climate policy.

Soil acidification and carbon sequestration are central challenges for sustainable agriculture, particularly across China’s extensive acidic red soil regions, which comprise 32.4% of the national soil area. This study evaluated the long-term effects of straw and manure incorporation on aluminum (Al) and iron (Fe) oxide fractions, soil organic carbon (SOC) sequestration, and crop yield in acidic red upland soil. A 33-year field experiment was conducted with four treatments: no fertilizer (CK), chemical fertilizer (NPK), NPK plus straw (NPKS), and NPK plus manure (NPKM). Soil samples were collected from three depths (0–10, 10–20, and 20–30 cm), and Al and Fe oxide fractions were quantified. Relationships among Al/Fe fractions, soil pH, and SOC were assessed using ANOVA, Pearson’s correlation, and Redundancy Analysis (RDA). Compared with CK, NPKM increased reactive Al (Alo) by 43.84%, 42.94%, and 43.06% and reactive Fe (Feo) by 132.98%, 91.54%, and 55.75% at 0–10, 10–20, and 20–30 cm, respectively. The highest carbon sequestration rate (0.21 t ha⁻¹ year⁻¹) occurred under NPKM in the 0–10 cm depth. Strong positive relationships were observed between reactive/non-crystalline Al and Fe oxides and both SOC sequestration and crop yield, particularly within the 0–20 cm depth, while SOC stock and CSR declined with depth across all treatments. These results highlight the critical role of manure in alleviating soil acidity, enhancing SOC stabilization capacity, and increasing crop productivity in acidic red upland soils. Overall, integrating organic amendments such as manure and straw substantially improves SOC accumulation and supports sustainable agricultural management in acidic red soils.

Water scarcity and the rising cost of chemical fertilizers pose major challenges to sustainable crop production in Egypt, particularly in sandy soils with low fertility. This study was conducted during the winters of 2022–2023 and 2023–2024 to investigate the combined effects of different irrigation levels and Nostoc algae extract on soil properties and wheat (Triticum aestivum) productivity. Three irrigation levels (100%, 80%, and 60% of crop evapotranspiration [ETc]) were evaluated with and without added algae. To analyze our data, we performed an analysis of variance (ANOVA) to evaluate differences among the treatments; correlation analysis was conducted to assess the relationships among soil properties and plant properties. The results showed that application of algae significantly increased soil organic matter under all irrigation treatments. In contrast, soil pH decreased in response to addition of algae, with the greatest reduction observed under the 60% ETc treatment (0.29 and 0.31 units in the first and second growing seasons, respectively). Water productivity differed significantly among treatments, following the order: 80% ETc > 100% ETc > 60% ETc (p ≤ 0.05). The application of algae under the 80% ETc regime increased water productivity by 12.01% and 12.19% in the first and second seasons, respectively, compared with the treatment without algae. Moreover, organic matter exhibited a strong positive correlation with N, P, and K contents in both straw and grain. The total yield reached its greatest level at 100% ETc with algae (5,526.43 ± 61.30 kg feddan⁻¹), whereas the lowest value was reported at 60% ETc without algae (2,880.97 ± 37.81 kg feddan⁻¹). Overall, application of algae contributed to improved soil properties, enhanced soil nutrients, structure and moisture retention, and mitigated yield losses associated with reduced irrigation. These findings suggest that integrating algae biofertilizers with deficit irrigation strategies can serve as a sustainable approach to improve wheat production in sandy soils under water-limited conditions.

Lime application represents an established approach for ameliorating soil acidity, and understanding its effects on the interactions between aluminum (Al) and iron (Fe) oxides and soil organic carbon (SOC) fractions is essential for promoting sustainable agricultural practices that enhance carbon sequestration. This investigation examined the interactions among Al and Fe oxides and SOC fractions under long-term fertilization and liming. A long-term field experiment was implemented with five treatments: CK (no fertilizer), N (nitrogen fertilizer), NCa (N plus lime), NPK (nitrogen, phosphorus, and potassium fertilizer), and NPKCa (NPK plus lime). Soil samples were obtained from three depths: 0–10, 10–20, and 20–30 cm. The findings revealed that lime application increased SOC by 20.84% under the N treatment but decreased SOC by 9.97% under NPK. At the 0–10 cm depth, dissolved organic carbon (DOC) was substantially higher under NCa (410.51 mg kg^–1) and NPKCa (372.83 mg kg^–1) compared with CK. Particulate organic carbon (POC) and mineral-associated organic carbon (MAOC) demonstrated consistent enhancement under NPK and NPKCa across all soil depths compared with CK. DOC exhibited significant positive correlations with both aluminum (Ald), reactive aluminum (Alo) and aluminum (Alp), indicating a key role of organically bound and reactive Al in carbon dynamics. Compared to the CK treatment, SOC stock increased significantly by 43.49% under NPK and by 36.82% under NPKCa. Structural equation modeling demonstrated that lime application mitigated the negative effects of free Al (Ald) on carbon sequestration, while Fe oxides (Fed) contributed positively to SOC stabilization. DOC showed no significant impact on carbon sequestration rate (CSR), while easily oxidizable carbon (EOC) negatively affected CSR directly. These results highlight the crucial role of lime in improving acidic soil conditions and enhancing the stability and sequestration of soil organic carbon.