Nitrogen

China has implemented extensive land restoration programs and now leads the world in artificial forest area. However, such plantations often face degradation, largely due to soil nutrient deficiency. In contrast, near-natural restoration tends to result in better soil quality, ecosystem integrity, and stability. This study focuses on three near-naturally restored sites on the Loess Plateau—a critical part of China’s National Ecological Security Barrier System, which has undergone substantial ecological restoration in recent decades. Using soil stoichiometry to assess nutrient balance and land sustainability, we investigated two forest types (Betula platyphylla, BP; Larix principis-rupprechtii, LP) and a mixed shrubland (Ostryopsis davidiana and Cotoneaster multiflorus, OD–CM). Soil profiles were sampled at 20 cm intervals from the surface to bedrock. We measured soil carbon (C), nitrogen (N), and phosphorus (P) contents, along with key environmental factors. The results show the following: (1) The two forest lands exhibited similar C and N levels, which were 1.23–1.26 and 1.40–1.51 times higher, respectively, than those in the shrubland. (2) Lower C/N (BP: 25.05; LP: 23.46) and higher N/P (BP: 4.83; LP: 5.00) in the forest lands indicated lower nitrogen limitation versus the shrubland (C/N: 28.55; N/P: 3.44). (3) Key influencing factors varied across land restoration types, indicating that the vegetation community’s composition mediates nutrient cycling through nutrient uptake and litter input. (4) Relative to plantations in the same region, near-naturally restored lands had 3.47–5.64 times higher C content and 1.51–2.51 times higher N content. Moreover, near-natural communities exhibited higher C/N (21.68–30.56) and C/P (85.92–132.97) compared to plantations (C/N: 8.8–13.1; C/P: 9.16–31.2), reflecting more efficient nitrogen and phosphorus utilization. Thus, near-natural land restoration enhances soil carbon sequestration, nitrogen fixation, and nutrient use efficiency on the Loess Plateau, supporting its promotion as a superior land management strategy for enhancing land sustainability and ecosystem services in this area.

Optimizing nitrogen fertilization and planting date is essential for improving forage maize productivity under semi-arid conditions. This study evaluated the effects of nitrogen application rates and planting dates on growth, forage yield, and quality of maize (Zea mays L.) in Upper Egypt. A two-year field experiment (2024–2025) was conducted at the Experimental Farm of Assiut University using a strip-plot design arranged in a randomized complete block design with three replications. Four planting dates (15 April, 15 May, 15 June, and 15 July) were assigned horizontally, while three nitrogen rates (167, 238, and 309 kg N ha⁻¹) were applied vertically. Growth traits, fresh and dry forage yield, dry matter percentage, crude protein content, and protein yield were recorded at 60 days after sowing. Results showed that planting date, nitrogen rate, and their interaction significantly affected most measured traits in both seasons. Sowing in mid-May consistently produced the highest plant height, chlorophyll content, fresh and dry forage yield, and protein yield. Increasing nitrogen application enhanced biomass production and forage quality, with the highest values generally recorded at 309 kg N ha⁻¹. The strongest yield response to nitrogen occurred when maize was sown at the optimal planting date, indicating that nitrogen utilization was closely linked to favorable environmental conditions. Phenotypic correlation and multivariate analyses revealed strong associations among vegetative growth traits and forage yield, with a single dominant factor explaining more than 91% of the variation in yield-related traits across seasons. Overall, the results demonstrate that synchronizing planting date with appropriate nitrogen fertilization is critical for maximizing maize forage yield and quality under semi-arid conditions. Mid-May sowing combined with adequate nitrogen supply represents an effective management strategy for forage maize production in Upper Egypt, while further research is needed to optimize nitrogen-use efficiency and long-term sustainability.

Biological nitrogen fixation (BNF) is crucial for enhancing soybean productivity while reducing reliance on mineral nitrogen fertilizers. The accurate estimation of BNF via the δ¹⁵N natural abundance method depends on reliable B-values, which represent plants that derive all their nitrogen from fixation. This study aimed to assess the B-values and symbiotic efficiency of Bradyrhizobium-inoculated soybean varieties using δ¹⁵N natural abundance techniques. Eight strains and five soybean varieties were evaluated in sterilized sand culture using a factorial completely randomized design under lath-house conditions. Plants were analyzed for δ¹⁵N, shoot N concentration, shoot N content, and symbiotic efficiency (SE). The applied treatments showed highly significant effects with strong interactions, reflecting substantial genotypic variation in symbiotic performance. Strain SD-53 produced the lowest δ¹⁵N values (−0.24 to 0.14‰) and the highest SE, with several strain–variety combinations surpassing N-fertilized controls. Shoot N concentration and content ranged from 0.96–3.16% and 9.90–52.73 mg plant⁻¹, respectively, and SE varied from 29.07 to 136.29%. δ¹⁵N showed strong negative correlations with SE and plant N traits. The study identified SD-53 as a promising inoculant candidate and generated the first regional soybean B-values (−0.24 to 0.14‰ for each tested variety and a mean of −0.08 ± 0.14‰) for Ethiopia. These values provide an important baseline for %Ndfa calculations and support future field validation and inoculant formulation.