Nitrogen loss in Brachiaria decumbens after application of glyphosate or glufosinate-ammonium

Henrique Coutinho Junqueira Franco,Milton Ferreira Moraes,Virginia Damin,Paulo Cesar Ocheuze Trivelin,Ademir Franco

doi:10.1590/s0103-90162008000400012

Abstract

Nitrogen losses from the soil-plant system may be influenced by herbicide applications. In order to evaluate N loss in brachiaria (Brachiaria decumbens) after application of the herbicides glyphosate and glufosinate-ammonium, an experiment was carried out in a greenhouse as a completely randomized design, with three treatments and six replicates. Treatments were as follows: i) desiccation of brachiaria-plants with glyphosate; ii) desiccation of brachiaria-plants with glufosinate-ammonium; and iii) control, without herbicide application. The plants were cultivated in 4 kg pots of sandy soil and fertilized with ammonium sulfate- 15N, (200 mg kg-1) in order to quantify the allocation of the fertilizer-N and its recovery in the soil-plant system. Plants treated with the herbicides had less N accumulation and less recovery of the fertilizer-N (15N) relative to the control. In the soil, the greatest recovery of 15N-fertilizer occurred for treatments where N was applied, possibly due to the occurrence of other N compound losses to the soil, like root exudation and root death. The total recovery of 15N-fertilizer in the soil-plant system was higher in the control than in the treated plants showing the direct action of the herbicides on nitrogen loss, and especially by the above-ground part of the brachiaria plants.

Highlights

Nitrogen fertilization is one of the recommended practices to obtain good productivities in agricultural systems
The dry mass yield of the above-ground parts and from the entire brachiaria plants was smaller in the glufosinate treatment (Table 1)
This difference could be linked to the rapid action of the herbicide, since plants receiving this herbicide showed earlier senescence than those treated with glyphosate

Summary

Introduction

Nitrogen fertilization is one of the recommended practices to obtain good productivities in agricultural systems. Nitrogen losses by the above-ground part of plants may contribute to increase ammonium levels in the atmosphere, e.g. NH -N emission values by plants in the order of 5-15 kg h3a-1 year-1 (Sutton et al, 1993). This nitrogen loss pathway could be responsible for 15-20% of all gaseous emissions of NH (Asman et al, 1998). The magnitude of natural nitrogen losses by the aerial part of crops may vary according to the grown species, plant developmental stage, nitrogen availability in the soil, stomatal conductance, leaf temperature, plant stress due to diseases, water deficit, NH level in the atmosphere, ammonium concentration in the plant, and the activity of the glutamine synthetase enzyme (Schjoerring et al, 1998; Parton et al, 1988). Some herbicides may affect one or more of these factors and, as a result, may increase N losses by the above-ground part of plants

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Results