Effects of Fertilizer Source, Application Strategy, and Water Regime on Nitrogen Loss Pathways Under Controlled Conditions

Abstract

Nitrogen (N) fertilization can cause environmental losses through ammonia (NH3) volatilization, nitrous oxide (N2O) emissions, and nitrate leaching. Urease (UI) and nitrification (NI) inhibitors, together with improved fertilization strategies, have been proposed to mitigate these losses. Under controlled conditions, this study evaluated the effects of UI and NI on N losses: (i) under contrasting water regimes, and (ii) different fertilization strategies. Two experiments were conducted using soil columns (0–20 cm) to quantify NH3 volatilization, N2O emissions, nitrate leaching, and soil residual N after fertilization. Treatments included urea, urea with a UI (Urea + UI), urea with a NI (Urea + NI), and calcium ammonium nitrate (CAN), evaluated under contrasting water regimes (dry and wet) and fertilization strategies (single-rate vs. split). NH3 losses reached up to 9.5% of applied N and were greater under dry conditions. Urea + UI reduced volatilization relative to urea (15–59%), while split applications reduced losses by 66–81%. Nitrous oxide emissions were low (≤ 0.026% of applied N) and showed no consistent treatment effects. Nitrate leaching was the dominant loss pathway (23.8–55.7% of applied N), highest under wet conditions and with CAN, whereas Urea + NI applied at a single-rate reduced leaching compared to full-rate urea. Residual mineral N was higher under dry conditions and split applications, particularly with NI. The effectiveness of N loss mitigation strategies was highly dependent on water regime. Under dry conditions, CAN or split-applied Urea + UI reduced NH3 volatilization, while under leaching-prone conditions, split Urea applications, especially when combined with a NI, improved soil N retention.