Comprehension of the long-term effects of irrigation on basic soil characteristics and quality is essential for sustainable land management and agricultural production, particularly in arid regions where water availability is limited. This study aimed to investigate long-term irrigation effects on soil quality, soil organic carbon (SOC), and nitrogen (N) stocks in the arid lands of Egypt. Seventy soil samples were collected and analyzed to determine various soil properties. A soil quality index (SQI), SOC, and N stocks were computed. ANOVA and PCA analyses were used to identify significant differences between alluvial soils in the southwest part of the investigated area and coastal marine soils in the northeast of the study area. The results demonstrated that most of the studied soil parameters had significantly greater values in alluvial compared to coastal marine soils. Long-term irrigation led to an 8.00% increase in SOC and 7.22% increase in N stocks compared to coastal marine soils production. Furthermore, a 39.53% increase was found in the SQI upon long-term irrigation practice. These results suggest that shifting from rain-fed in coastal marine areas to irrigated production systems in alluvial fields can improve soil quality, SOC, and N stocks. Therefore, further studies are required to investigate the impact of additional factors, such as irrigation method and salinity status of sub-surface soil layers, to enhance agricultural productivity and sustainable land use.

Biochar derived from poultry manure increases nutrient availability and promotes plant growth. This study investigated the effect of biochar with mycorrhizal and/or plant growth-promoting rhizobacteria on soil fertility, chemical properties, oil, and seed yield of Black Cumin (Nigella sativa L.) plants. A split-plot design with three replicates was employed, with biochar derived from poultry litter (BC) applied at rates of 0, 5, and 10 t ha⁻¹, with beneficial microbes such as arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria (PGPR) affecting the growth of Black Cumin plants, and some soil properties, such as pH, electrical conductivity (EC), soil organic matter (SOM) and fertility index (FI), showing significant differences (p ≤ 0.05) among biochar and/or bio-fertilizer treatments. All biochar treatments with or without bio-fertilizers significantly increased pH, EC, OM and FI in comparison to the control treatment. The results demonstrated that applying biochar at the highest rate (10 t ha⁻¹) increased fresh and dry capsule weights by 94.51% and 63.34%, respectively, compared to the control treatment (C). These values were significantly increased by 53.05 and 18.37%, compared to untreated plants when combined with AMF and PGPR. Furthermore, when biochar was applied in conjunction with both AMF and PGPR, fresh and dry capsule weights saw significant increases of 208.84% and 91.18%, respectively, compared to the untreated control treatment. The interaction between biochar, AMF, and PGPR significantly improved plant growth, yield, soil properties, and the fixed and volatile oil content of Black Cumin. These findings suggest that the combined application of biochar, AMF, and PGPR enhances nutrient availability and uptake, leading to improved growth and higher yields in Black Cumin plants, resulting in increased yield production.

The relationships between soil aggregates, aggregate-associated carbon (C), and soil compaction indices in pomegranate orchards of varying ages (0–30 years) in Assiut, Egypt, were investigated. Soil bulk density (Bd) and organic carbon (OC) content increased with orchard age in both the surface (0.00–0.20 m) and subsurface (0.20–0.40 m) layers 0.20–0.40 m). The percentage of macroaggregates (R_0.25) and their OC content in the aggregate fraction > 0.250 mm increased as the pomegranate orchard ages increased in the surface layer (0.00–0.20 m). Older pomegranate orchards show improved soil structure, indicated by higher mean weight diameter (MWD) and geometric mean diameter (GMD), alongside reduced fractal dimension (D) and erodibility (K). As orchard ages increased, maximum bulk density (B_Max) decreased due to an increase in OC, while the degree of compactness (DC) increased, reaching a maximum at both soil layers for the 30 Y orchards. Soil organic carbon and aggregate-associated C significantly influenced B_Max, which led to reducing the soil compaction risk. Multivariate analyses identified the >2 mm aggregate fraction as the most critical factor influencing the DC, soil compaction, and K indices in pomegranate orchards. The OC content in the >2 mm aggregates negatively correlated with B_Max, DC, and K but was positively associated with MWD and GMD. Moreover, DC and Bd decreased with higher proportions of >2 mm aggregates, whereas DC increased with a higher fraction of 2–0.250 mm aggregation. These findings highlight the role of aggregate size fractions and their associated C in enhancing soil structure stability, mitigating compaction, and reducing erosion risks in pomegranate orchards.

Excessive nitrogen (N) fertilization poses environmental risks and can induce micronutrient imbalances that limit crop productivity. This two-season field study (2024/2025–2025/2026) investigated the interactive effects of four nitrogen (N) rates (0, 75, 150, and 225 kg N ha⁻¹) and four foliar iron (Fe) concentrations (0, 100, 200, and 300 mg L⁻¹) on Canola (Brassica napus L.) yield and oil quality under the arid conditions of Upper Egypt. The highest N rate (225 kg N ha⁻¹) increased seed yield by 240% and oil yield by 271% compared to the unfertilized control, but substantially reduced Nitrogen Use Efficiency (NUE), with Partial Factor Productivity of Nitrogen (PFPN) declining from 52.5 to 11.2 kg seed kg⁻¹ N. Foliar Fe at 300 mg L⁻¹ enhanced seed yield by an additional 29.9–37.0%. The combined N₃Fe₃ treatment produced maximum biological (8258 kg ha⁻¹), seed (2892 kg ha⁻¹), and oil (812 kg ha⁻¹) yields, establishing a maximum yield threshold under the tested conditions. However, at the highest N rate, there were no statistically significant differences in oil yield among Fe₁ (100 mg L⁻¹), Fe₂ (200 mg L⁻¹), and Fe₃ (300 mg L⁻¹), indicating that the lowest tested Fe concentration was sufficient to achieve yields comparable to higher rates. The N × Fe interaction was characterized as additive for seed yield but synergistic for leaf iron uptake and translocation. While integrated N-Fe fertilization offers a promising strategy for sustaining Canola productivity in nutrient-poor calcareous soils, the declining N use efficiency at higher N rates and the absence of economic and environmental indicators (nitrate leaching, nitrous oxide (N₂O) emissions) highlight the need for further research to identify true optima for arid-zone Canola production.