Herbicides increase emission of ammonia by pearl millet and congo grass

Abstract

In previous works, we demonstrated that some herbicides could increase N losses from the soil–plant system under greenhouse conditions, but the N-output pathways were not investigated.In this context, the aim of this work was to evaluate ammonia(NH 3) emission by soil and plants and the total-N accumula-tion in the straw following herbicide application to pearl millet(Pennisetum glaucum) and congo grass (Urochloa ruziziensis).Two field experiments were conducted in a randomized block,with a factorial design and eight replicates per treatment. The treatments were: 1-control: without herbicide application, 2-glyphosate, 3-glufosinate-ammonium, and 4-paraquat. Periodic measurements of NH 3 emission by plants or soil at 48-h intervals were considered as repeated measurements. At the end of the experiment, the dry mass, ammonium (NH4+) in both plant tissues and soil, and total N in shoots were measured. All evaluated herbicides increased emission of NH 3 by pearl millet and congo grass with net losses ranging from 1.5 to 7.0 kg ha –1 ofNH 3 after herbicide application, but soil NH 3 emission was not affected. In congo grass, all herbicides reduced total N and dry mass content in plant tissues, but only the glyphosate herbicide reduced it in pearl millet. Herbicide usage increases emission of ammonia by plants and can decrease the total-N accumulation in cover crop straw. Further research should be done to inves-tigate how these ammonia losses and changes in total N from aboveground biomass affect crop production as well as the rec-ommended N fertilizer application rates.