Glyphosate [(N-(phosphonomethyl)glycine] is a post emergence herbicide used to weed control, cover crop desiccation in conservationist systems and pre-harvesting desiccation. The widespread use of this herbicide has been related to some environmental concerns. In the last years, some studies have shown that glyphosate could affect nitrogen (N) transformations in the soil-plant systems, enhancing nitrogen losses and changing N mineralization rates (Haney et al. 2002, Damin et al. 2008, 2010a, Castoldi et al. 2012. Damin et al. (2008) demonstrated that signal grass (Urochloa decumbens) desiccation with glyphosate enhances N losses from plant-soil system, with more than 16% of the N from fertilizer being lost 15 days after herbicide application. The higher N losses observed after glyphosate application may be related to ammonia (NH 3 ) emission by plants. The main factors driving NH 3 emission are the NH 4 + content in leaves, stomata conductance, plant's age and species and NH 3 levels in the atmosphere (Loubet et al. 2002, Mattsson andSchjoerring 2002). Herbicides affect more than one of these factors, so their application may affect NH 3 emission by plants.NH 3 emission by agricultural areas account for 10% up to 20% of global NH 3 emission (Behera et al. 2013). It is an important process of N output in agriculture lands, reducing N use efficiency; moreover, it is an environmental concern as well (Galloway et al. 2003).In Brazilian agroecosystems, signal grass is one of the most widespread weeds (Neto et al. 2008). Moreover, it is used as a cover crop in no-till systems, in the area between rows of plant species such as coffee (Coffea spp.) and orange (Citrus spp.) and for farming-cattle integration systems; all these systems use glyphosate to control weeds and/or kill cover crops. Within this context, the objective of this study was to evaluate NH 4 + and total nitrogen (N tot ) levels in plant's tissues and NH 3 emission by foliage after glyphosate application on signal grass.
Emissions of ammonia following glyphosate application on Urochloa decumbens
ABSTRACTThis work was carried out with the objective of evaluating the ammonium (NH 4 + ) levels and emissions of ammonia (NH 3 ) after glyphosate application on signal grass (Urochloa decumbens). Two experiments were carried out and the following treatments were used: (1) Control -mechanic harvest with no herbicide application on signal grass; (2) Glyphosate -signal grass desiccation with the herbicide glyphosate. Ammonium (NH 4 + ); total nitrogen (N tot ) levels in plant's tissues (experiment 1) and ammonia (NH 3 ) emission by the plants or the soil (experiment 2) were evaluated over time, under field conditions. Signal grass desiccation with the herbicide glyphosate enhanced NH 4 + levels from 2-24% of the N tot at 12 days after herbicide application. The cumulative NH 3 emission by leaves were increased from 2.8-5.3 kg/ha 30 days after herbicide application. Glyphosate application increases NH 3 losses by plant, but it does not affect the NH 3 emissions by ...