N budget and NH3 exchange of a grass/clover crop at two levels of N application

B Herrmann, SK Jones, J Fuhrer, U Feller, Albrecht Neftel

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23 Citations (Scopus)

Abstract

Atmospheric ammonia (NH3) exchange during a single growing season was measured over two grass/clover fields managed by cutting and treated with different rates of mineral nitrogen (N) fertilizer. The aim was to quantify
the total NH3 exchange of the two systems in relation to their N budget, the latter was split into N derived from symbiotic fixation, from fertilization, and from the soil. The experimental site was located in an intensively managed agricultural area on the Swiss plateau. Two adjacent fields with mixtures of perennial ryegrass (Lolium perenne L.), cocks foot (Dactylis glomerata L.), white clover (Trifolium repens L.) and red clover (Trifolium pratense L.) were used. These were treated with either 80 or 160 kg N ha−1 applied as NH4NO3 fertilizer in equal portions after each of four cuts. Continuous NH3 flux measurements were carried out by micrometeorological techniques. To determine the contribution of each species to the overall NH3 canopy compensation point, stomatal NH3 compensation points of the individual plant species were determined on the basis of NH4 + + NH3 (NHx)
concentrations and pH in the apoplast. Symbiotic N2 fixation was measured by the 15N dilution method. In the field with the lower rate of mineral N application, the clover fraction was higher, and a higher symbiotic N2 fixation rate completely compensated for the lower mineral N input. During the measurement period, except after N fertilization, NH3 concentration ([NH3]) above the canopy was between 3 and 4 μg m−3, which was generally higher than the measured canopy NH3 compensation point. Thus, deposition from the atmosphere to the grass/clover canopy was predominant, and the system acted as net sink for NH3. The total amount of N emitted as NH3 was slightly higher for the high N treatment compared to the low N treatment but accounted for less than 1% of the N removed by cutting in both treatments. The results show that net NH3 emission from the frequently cut grass/clover field was restricted to short periods after ammonium nitrate application, and that on a seasonal basis
fertilizer N and N derived from N2 fixation had equal effects on the exchange of NH3 between the canopy and the atmosphere.
Original languageEnglish
Pages (from-to)243–252
JournalPlant and Soil
Volume235
Issue number2
DOIs
Publication statusPrint publication - Aug 2001
Externally publishedYes

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