Document Type : Research Paper

Authors

• Seyyede Fahime Safdari ¹
• Fatemeh Benakashani ²
• Azam borzouei ³
• Farhad Saberali ⁴

¹ Agronomy and plant breeding science-Faculty of Agricultural Technology (Aborihan)-University of Tehran

² Faculty of Agricultural Technology (Aborihan)- University of Tehran

³ Agricultural Research School, Nuclear Science and Technology Research Institute

⁴ Faculty of agriculture-Tarbiat Modares

Abstract

Objective: Nitrogen plays a pivotal role in modern agriculture as a key determinant of crop productivity, particularly in oilseed crops like rapeseed (Brassica napus L.). However, nitrogen use efficiency (NUE) in agricultural systems remains alarmingly low, with significant nitrogen losses occurring through nitrification, leaching, and volatilization processes. These losses not only represent economic waste but also contribute to serious environmental concerns, including groundwater contamination and greenhouse gas emissions. This study was designed to comprehensively evaluate the effects of different nitrogen fertilizer levels combined with the nitrification inhibitor nitrapyrin on growth parameters, yield components, and nitrogen use efficiency of two commercially important rapeseed genotypes under the warm and humid agro-climatic conditions of Pakdasht, Tehran province.
Method: The experiment was conducted as a split-plot arrangement within a randomized complete block design with three replications during the 2021-2022 growing season. The main factor included two rapeseed genotypes (Roshana and Zafar), while the sub-factor consisted of five urea fertilizer levels (0, 50, 100, 150, and 200 kg ha⁻¹) with and without nitrapyrin (2-chloro-6-trichloromethyl pyridine). Measured traits included seed yield, biological yield, harvest index, plant height, and other morphological characteristics.
Results: The study revealed several important findings: (1) Nitrogen application up to 150 kg ha⁻¹ significantly improved all growth and yield parameters, with diminishing returns observed at higher application rates; (2) Nitrapyrin application consistently enhanced nitrogen use efficiency by 18-22% across all nitrogen levels; (3) The combination of 150 kg N ha⁻¹ with nitrapyrin produced optimal results, increasing seed yield by 23.5% (3542 kg ha⁻¹) compared to the same nitrogen level without inhibitor; (4) Biological yield showed an 11.2% improvement with nitrapyrin use; (5) The inhibitor extended nitrogen availability in the ammonium form by 3-4 weeks, better matching crop demand; (6) Environmental nitrogen losses were reduced by 28-35% with nitrapyrin application. (7) Grain nitrogen percentage and harvest index were significantly influenced by varying nitrogen fertilizer levels. Increasing nitrogen application rates led to a rise in both harvest index and grain nitrogen concentration. However, shoot nitrogen content remained unaffected by the different nitrogen treatments.
Conclusions: This research demonstrates that the judicious combination of moderate nitrogen fertilization (150 kg ha⁻¹) with nitrapyrin represents an optimal management strategy for rapeseed production in warm, humid environments. The treatment balanced crop nutritional requirements with environmental protection, improving nitrogen use efficiency while reducing potential pollution. These findings have significant implications for sustainable nitrogen management protocols in oilseed production systems, particularly in regions facing similar climatic challenges and environmental concerns. Future research should investigate long-term soil health impacts and economic feasibility of this approach across different agro-ecosystems.

Keywords

• Rapeseed
• Nitrogen management
• Nitrapyrin
• Seed yield
• Sustainable agriculture