Effect of Environmental Factors on Ammonia Volatilization from a Urea‐Fertilized Soil

Abstract

Abstract A greenhouse experiment using 15 N followed by wind tunnel experiments using a micrometeorological technique were conducted to identify some of the factors that contribute most significantly to ammonia (NH 3 ) volatilization in a simulated semiarid environment following application of urea. An Aridic Calciustolls with high urease activity was subjected to a variety of initial soil moisture contents, rainfall patterns, wind speeds, air‐humidity, and urea application methods. Losses of broadcast urea‐N in the greenhouse at 42‐d harvest, presumably due to NH 3 volatilization, were reduced from 40% with a first rain of 1 cm (7 d after fertilizer application) to 13% with a first rain of 4 cm. Nitrogen losses were increased by 8% when initial soil moisture was increased from 21% (≅ permanent wilting point or PWP) to 31%. Wind tunnel experiments verified that nitrogen can be conserved either by heavy initial rain events (showing no NH 3 volatilization with application of 2.5 cm rain immediately after urea application) or by banding of urea at a depth of 2.5 cm. Losses were maximized by maintaining adequate moisture in the topsoil for urea hydrolysis without inducing leaching, either by humidifying the air between 80 and 95% or by applications of 8 mm rain every 3 d. Increasing wind velocity from 1.7 to 3.4 ms −1 reduced NH 3 loss from 19 to 7.5%, likely due to more rapid drying of the soil surface.