Measurement and Simulation of Ammonia Volatilization From Urea Fertilizer in Cropping and Pasture System.

Ammonia (NH₃) volatilization is an important pathway in soil N cycling and often responsible for the low efficiency of N fertilizer in plant-soil systems.  The NH₃ volatilization is strongly influenced by soil and climatic factors and management practices. The quantifying NH₃ volatilization is a technically challenge and costly exercise.

We present the NH₃ volatilization losses from the field experiments after the nitrogen fertilizer application in wheat, maize and pasture systems in Australia and China under different soil and climate conditions and management practices. The NH₃ volatilizations were measured by micrometrological methods of full profile (mass balance), gradient fluxes and the recently developed technique of open path laser/FTIR- Lagrangian model of atmospheric dispersion.  

NH₃ volatilization accounts up to up to 50% total N applied to alkaline in the North China Plain, up to 20% in the acidic pasture soils in Australia. The fertilizer application and irrigation methods strongly influence the NH₃ volatilization as well as soil and climate conditions.  Green urea, a commercial product containing NBPT as a urease inhibitor, was effective in reducing the NH₃ volatilisation (up to 90% less) when applied to wheat crop and pasture by surface broadcasting.   

A NH₃ volatilization sub-model was developed under the simulation framework of Water and Nitrogen Management Model (WNMM). A unique feature of this simulation component is the introduction of fertilizer N distribution function in soils for different applying methods, surface broadcasting, surface broadcasting followed by irrigation and deep placement. This sub-model calculates ammonia volatilization from surface and subsurface soil separately. For the surface layer, ammonia volatilization is controlled by soil temperature and wind speed, while for the subsurface soil layer, it is regulated by soil temperature, soil moisture, CEC and depth. The effect of localized pH surrounding urea granules and urine patches due to urea hydrolysis has been simulated, which is the main cause of NH₃ volatilization in acidic soils.  The model also incorporate the effect of urease inhibitor.