NH3 SOIL AND SOIL SURFACE GAS MEASUREMENTS IN A TRITICALE WHEAT FIELD

We present a new approach for a continuous determination of NH3 concen tration in the open pore space of the soil and on the soil surface. In a semi-permeable membrane of 0.5 m length a flow of 0.5 s1pm maintain ed. In the tube the NH3 concentration adjusts itself to the surroundin g air concentration by diffusion through the membrane. Continuous meas urements have been performed in a triticale wheat field over a period of several weeks in a field experiment at Bellheim (FRG) during June a nd July 1995 within the frame of the European program EXAMINE (Exchang e of Atmospheric Ammonia with European Ecosystems). Soil concentration s are generally below the detection limit of 0.1 mu gm(-3). We conclud e, that the investigated soil is generally a sink for NH3. The NH3 con centration on the soil surface shows a diurnal variation due to a comb ination of physico-chemical desorption and adsorption phenomena associ ated with changes in wetness of the surrounding surfaces and the NH3 c oncentration in the canopy. (C) 1998 Elsevier Science Ltd. All rights reserved.