Pattern of volatilized nitrogen loss from dryland kikuyu pastures after fertilization

Abstract

The pattern of nitrogen (N) loss through volatilization as ammonia (NH₃) may have important fertilizer management implications. A micrometeorological mass balance was used to measure this pattern after application of limestone ammonium nitrate (LAN; 28% N) and urea (46% N). Variables monitored included air temperature, relative humidity (RH), wind speed, and rainfall. The influence of these variables on patterns of NH₃ loss was assessed graphically and by using Spearman's ranked correlation analysis. A daily pattern of loss was observed in the flux of NH₃, with the greatest losses occurring between 10h00 and 14h00 on every sampling day. High temperatures and wind speeds promoted losses whilst rainfall events (in excess of 5 mm) inhibited losses, apparently by transporting applied fertilizer into the soil profile. Losses were suppressed at low temperatures, low wind speeds, and high RH. The highest overall loss recorded (3.7% of applied N) was lower than that expected for sub‐tropical conditions.