Measurement, Simulation and Mitigation of Ammonia Volatilization From Intensive Agriculture.

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.  

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. 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.

NH₃ volatilization accounts up to up to 50% total N applied to alkaline in the North China Plain, up to 29% in the acidic pasture soils in Australia and 70% of dietary N in the intensive feedlot in Australia. The fertilizer application and irrigation methods strongly influence the NH₃ volatilization as well as soil and climate conditions.  The WNMM model satisfactorily simulated NH₃ volatilization from soil under different agricultural systems and different application methods, which can be used to identify the better management practices to reduces nitrogen losses and improve fertilizer use efficiency. The incorporation of urea fertilizer into soils and irrigation immediately followed urea application reduced NH₃ volatilization by up to 75%. Application of urease inhibitor with urea in rain-feed wheat resulted in significant reduction in NH_3­ volatilization by up to 80%. Application lignite (brown coal) into the feedlot manure reduced NH₃ volatilization by more than 50%.