Effect of Calcium Cyanamide as an Alternative Nitrogen Source on Growth, Yield, and Nitrogen Use Efficiency of Short-Day Onion

Effective nitrogen (N) management in agriculture is vital to optimize crop growth and yield while minimizing environmental impact. Conventional nitrogen (N) sources, such as urea, have limitations in promoting growth and reducing N leaching. A two-year field experiment was carried out to investigate the effects of calcium cyanamide (CaCN₂) as a slow-release N source on short-day onion growth, yield, and N use efficiency (NUE). Six types of N sources were administered: (i) an initial application of 80 kg ha⁻¹ N in the form of CaCN₂ before planting; (ii) an initial application of 80 kg ha⁻¹ N in the form of CaCN₂ before planting, followed by a topdressing of 50 kg ha⁻¹ N in the form of limestone ammonium nitrate (LAN); (iii) an initial application of 80 kg ha⁻¹ N in the form of CaCN₂ before planting, followed by a topdressing of 50 kg ha⁻¹ N in the form of urea; (iv) an initial application of 80 kg ha⁻¹ N in the form of LAN before planting, followed by a topdressing of 50 kg ha⁻¹ N in the form of LAN; (v) an initial application of 80 kg ha⁻¹ N in the form of urea before planting, followed by a topdressing of 50 kg ha⁻¹ N in the form of urea; and (vi) control (0 kg ha⁻¹ N). Preplant CaCN₂ (80 kg ha⁻¹ N) outperformed the standard fertilizers used in onion as an N source (urea and LAN) by improving growth and yield, and reducing N leaching. Preplant CaCN₂ topdressed with either LAN or urea led to a significant increase in plant growth and total yield compared to using LAN or urea alone. The application of CaCN₂, followed by topdressing with either LAN or urea, decreased onion bolting by 1.6% and 1.83%, respectively, compared to the control. The study suggests that applying LAN or urea as a topdressing to preplant CaCN₂ enhances N utilization efficiency, leading to increased onion bulb yield and quality while reducing N leaching. This approach can help mitigate farm-level environmental pollution and provide valuable insights for improving onion production and sustainable agriculture practices in South Africa.