The combined effects of slope gradient, rainfall intensity, and nitrogen fertilizer source on infiltration, runoff, soil loss, and nitrogen (N) leaching in agricultural areas are not thoroughly understood, despite their critical importance in sustainable agriculture. Previous studies have focused on these factors individually, leaving a significant gap in knowledge regarding their synergistic impact. Investigating the interplay between slope gradients, rainfall intensities, and N fertilizer sources is vital to developing effective soil and water conservation strategies and implementing sustainable agricultural practices. This study is comprised of two experiments. Experiment 1 was designed as a 3 × 2 × 3 factorial arrangement, incorporating three levels of rainfall intensity (RI) (45, 70, and 100 mm/h), two slope gradients (5 and 8°), and three soil types (sandy loam, silt loam, and clay loam), aimed at assessing runoff, infiltration, and soil loss. Experiment 2, laid out as 3 × 2 × 3 × 3 factorial, expanded on this, adding N fertilizer source (urea, CaCN₂, and limestone ammonium nitrate (LAN) at 130 kg/ha N) and assessing N leaching alongside the previous metrics. Both experiments used a rotating disc rainfall simulator and were replicated four times. Results revealed that steeper slopes (8°) led to increased runoff and soil loss, impeding infiltration, while gentler slopes (5°) facilitated greater infiltration and minimized soil loss. Rainfall intensity played a significant role, with 70 mm/h/5° combinations promoting higher infiltration rates (48.14 mm/h) and 100 mm/h/8° resulting in lower rates (37.07 mm/h for sandy loam and silt loam, 26.09 mm/h for clay loam). Nitrogen leaching varied based on N source; urea at 130 kg/ha N led to higher losses (7.2% in sandy loam, 6.9% in silt loam, 6.5% in clay loam), followed by LAN (6.9% in sandy loam, 6.7% in silt loam, 6.3% in clay loam) while CaCN₂ at the same rate resulted in lower N losses (6.4% in sandy soil, 4.4% in silt loam, 4.2% in clay soil). This research highlights the critical need to consider both slope gradient and rainfall intensity in conjunction with appropriate nitrogen fertilizer sources when developing strategies to mitigate soil erosion and nutrient loss in agricultural settings.

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.

Onion (Allium cepa) is one of the world’s most consumed, nutrient-dense foods, low in calories and containing a rich amount of major bioactive compounds, vitamins, and minerals. The purpose of this study was to determine the influence of different nitrogen (N) fertilizer sources on the nutritional and phytochemical qualities of short-day onions. A white-type onion (cv. Texas Grano) was subjected to different fertilizer application treatments, namely (i) pre-plant base application of 80 kg ha⁻¹ N from CaCN₂, alone or in combination with (ii) top-dressing with 50 kg ha⁻¹ N from limestone ammonium nitrate (LAN), or (iii) top-dressing with 50 kg ha⁻¹ N from urea, (iv) pre-plant base application of 80 kg ha⁻¹ N from LAN and top-dressing with 50 kg ha⁻¹ N from LAN, (v) pre-plant base application of 80 kg ha⁻¹ N from urea and top-dressing with 50 kg ha⁻¹ N from urea, and (vi) 0 kg ha⁻¹ N. Pre-plant application of CaCN₂ (80 kg ha⁻¹ N) outperformed standard onion fertilizers, urea (130 kg ha⁻¹ N) and LAN (130 kg ha⁻¹ N), significantly enhancing total phenolic content, antioxidant activity, and calcium (Ca) and potassium (K) content in onion bulbs. Applying 50 kg ha⁻¹ N from urea as top-dressing with the pre-plant application of CaCN₂ (80 kg ha⁻¹ N) elevated total phenolics (5.48 mg GAE g⁻¹) and flavonoids (0.741 mg CE g⁻¹) in the onion bulbs. The highest antioxidant activity (55.9%) and free radical scavenging activity (26.3%) were achieved with top-dressing 50 kg ha⁻¹ N from LAN following CaCN₂ pre-plant application. Application of CaCN₂ + urea also significantly increased onion bulb potassium (2335 mg kg⁻¹) and calcium (828 mg kg⁻¹) contents, while CaCN₂ combined with LAN improved magnesium (123.3 mg kg⁻¹) content. This study recommends pre-plant CaCN₂, top-dressed with either LAN or urea, for improved phytochemical components, antioxidant activities, and certain mineral content in onion bulbs. These findings present a practical approach for cultivating nutrient-rich and phytochemically abundant onion bulbs, promoting improved human health.

Calcium cyanamide (CaCN₂), commercially known as Perlka^®, is re-emerging as a multifunctional nitrogen (N) fertilizer with significant agronomic and environmental advantages. Composed of 19.8% nitrogen and 50% calcium oxide (CaO), CaCN₂ not only supplies slow-release nitrogen but also acts as a liming agent, improving soil pH and structure. Its transformation pathway: cyanamide → urea → ammonium → nitrate—ensures a gradual nitrogen release that aligns with crop demand, enhances nitrogen use efficiency, and minimizes nitrate leaching and nitrous oxide emissions. Additionally, the presence of dicyandiamide, a known nitrification inhibitor, further stabilizes nitrogen in the soil. Field studies across diverse cropping systems, including curly endive and short-day onions, have demonstrated that CaCN₂ improves yield, crop quality, and soil health. In onions, preplant application of 80 kg ha⁻¹ N from CaCN₂ increased bulb yield by up to 18%, enhanced phytochemical content (e.g., phenolics and flavonoids), and reduced nitrate leaching by over 40% compared to urea and limestone ammonium nitrate (LAN). In curly endive, CaCN₂ significantly improved ascorbic acid, total soluble solids, and phenolic content, particularly in fall-grown crops, while reducing nitrate accumulation and improving physiological and recovery efficiency of applied nitrogen. Beyond its role as a nutrient supplier, CaCN₂ exhibits biocidal properties that suppress soil-borne pathogens such as Sclerotinia and Plasmodiophora brassicae, reduce weed pressure, and stimulate beneficial microbial activity. Its high calcium content also addresses physiological disorders linked to calcium deficiency, such as tip-burn and blossom-end rot. However, proper application timing and dosage are critical to avoid phytotoxicity, especially in sensitive crops. This review synthesizes current knowledge on CaCN₂’s chemical behavior, agronomic performance, and environmental implications, and identifies research gaps to guide its optimized use in climate-smart and resource-efficient agriculture.