Nitrogen Matters: Assessing the Effects of Nitrogen Fertilization on Maize Growth and Grain Productivity

Nitrogen deficiency is a major constraint on maize (Zea mays L.) productivity in Afghanistan, where poor soil fertility limits yields. This study investigated the effect of urea fertilizer on maize growth, physiology, and yield under semi-arid conditions in Balkh Province with a Calcisols soil type, focusing on maize cultivated for grain production. A field experiment was conducted in 2019 using a randomized complete block design with three replications and four nitrogen levels: 0 (control), 38.4, 76.8, and 115.2 kg ha−1. The region consists of fertile alluvial plains suitable for crop cultivation, though maize productivity is constrained by soil nutrient limitations, especially nitrogen deficiency. The soil at the experimental site is silty loam in texture, moderately fertile with alkaline pH (8.1), low organic matter (0.5%), and limited available nitrogen (15 mg kg−1). Growth traits (plant height, leaf number, leaf area, SPAD value), physiological parameters (leaf area index, crop growth rate, biomass), and yield components (cob length, cob diameter, seed number, 100-seed weight, biological yield, and Brix content) were recorded. Results showed that nitrogen application significantly improved all traits compared to the control. The highest values for plant height (260.2 cm), cob length (31.67 cm), biological yield (216.6 t ha−1), and Brix content (8.6%) were observed at 115.2 kg ha−1, although 76.8 kg ha−1 produced nearly similar results. Correlation analysis revealed strong positive associations between SPAD values, vegetative traits, and yield. The findings indicate that 115.2 kg ha−1 urea is an efficient and practical nitrogen rate for enhancing maize productivity under Afghan conditions.