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 5mm) 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 the expected for sub-tropical conditions.

Keywords: air temperature; ammonia; ammonium nitrate; dryland; fertilization; fertilizer; kikuyu pastures; limestone ammonium nitrate; natal; nitrate; nitrogen; pasture; rainfall; relative humidity; south africa; ukulinga research station; urea; wind speed

African Journal of Range & Forage Science, 10(2): pp. 86-91