Effects of Rainfall Intensity and Slope on Infiltration Rate, Soil Losses, Runoff and Nitrogen Leaching from Different Nitrogen Sources with a Rainfall Simulator

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.