Glufosinate treatment of weeds results in ammonia emission by plants

Herbicide treatment caused a rapid increase in shoot ammonium concentration and the ammonium portion of the plant total nitrogen ranged from 0.6 to 0.9% and from 17 to 44% before and after PPT application, respectively. S. nigrum showed a strong increase in ammonium portion (35%) followed by a decrease (20%), which may have resulted from ammonia volatilization. The difference in total shoot nitrogen content per ground area at the start and 2 weeks after PPT application averaged for the three C3 weed species to a nitrogen loss of ca. 0.4 g N m−2 or approximately 13% of the total nitrogen in the weed canopy. Analysis of the apoplastic fluid yielded an increase in ammonium concentration and a pH decrease after an initial increase on day 1 after the PPT treatment. In order to evaluate the potential for ammonia loss, the Γ-value was calculated for both apoplastic and tissue water. S. nigrum showed the most dramatic increases in both apoplastic and tissue-water Γ-values 4 days after PPT treatment. The calculated stomatal NH3 compensation point was strongly elevated after PPT treatment. However, temporal changes of apoplastic pH and ammonium concentration varied between the species and the modelled ammonia emission ranged from 0.03 to 0.09 g N m−2. It is concluded that PPT application results in an ammonia emission of ca. <10% of the canopy nitrogen content. This is negligible with respect to the nitrogen balance of an agroecosystem; however, the ammonia pollution of the atmosphere has to be taken into account.