Synergistic Biochar–Nitrogen Application Enhances Soil Fertility and Compensates for Nutrient Deficiency, Improving Wheat Production in Calcareous Soil

Nutrient deficiencies, low organic matter content, and a limited soil–water saturation percentage in calcareous soils hinder plant growth and crop production. To address these challenges, sustainable and green-based farming practices have been introduced. This study investigates the synergistic effects of biochar and nitrogen levels as sustainable solutions for improving soil fertility and supporting wheat growth in calcareous soils. A pot experiment assessed the effects of biochar (5-, 10-, and 15-tons ha −1 ) and nitrogen levels (60, 90, and 120 kg ha −1 ) on soil physicochemical properties, nutrient availability, and wheat growth. The randomized complete block design included three replicates and a control. The results highlight that the highest biochar rate (15 tons ha −1 ) combined with the highest nitrogen level (120 kg ha −1 ) significantly ( p ≤ 0.05) improved soil physicochemical properties and nutrient status. Notably, soil pH increased by 2.8%, electrical conductivity by 29.8%, and soil organic matter by 185%, while bulk density decreased by 22.3%. Soil total nitrogen surged by 163.7%, soil–water saturation percentage by 27.2%, plant-available phosphorus by 66.8%, and plant-available potassium by 96.8%. Wheat growth parameters also showed marked improvement, with plant height up 29.7%, spike length by 20.7%, grains per spike by 41.5%, thousand-grain weight by 24.7%, grain yield by 81.3%, and biological yield by 26.5%. There was a strong positive correlation between enhanced soil properties and improved wheat growth, except for soil bulk density, which showed a negative correlation. This underscores the role of biochar in boosting soil fertility and crop productivity. A principal component analysis further validated these findings, suggesting that integrating biochar with appropriate nitrogen fertilization offers a sustainable strategy to enhance soil health, manage nutrient availability, and strengthen crop yields in calcareous soil. Biochar application combined with elevated nitrogen levels significantly enhances soil fertility and wheat productivity in semi-arid regions, offering a sustainable solution for improving calcareous soils. Future studies should explore the long-term impacts and scalability of this approach.