IINNNTTTEEERRRNNNAAATTTIIIOOONNNAAALL AAgggrrroooppphhhyyysssiiicccss www.international-agrophysics.org Int. Agrophys., 2013, 27, 203-209 doi: 10.2478/v10247-012-0086-7 Adsorption of glyphosate and aminomethylphosphonic acid in soils N. Rampazzo*, G. Rampazzo Todorovic, A. Mentler, and W.E.H. Blum Institute of Soil Research, Department of Forest and Soil Sciences, University of Natural Resources and Life Sciences, Peter Jordan-Strasse 82, 1190 Vienna, Austria Received February 15, 2012; accepted October 26, 2012 A b s t r a c t. The results showed that glyphosate is initially Glyphosate (N-(phosphonomethyl)glycine) is the active adsorbed mostly in the upper 2 cm. It is than transported and ad- compound in Roundup Max, a post-emergency non-selec- sorbed after few days in deeper soil horizons with concomitant tive broad spectrum herbicide widely applied in agricultural increasing content of its metabolite aminomethylphosphonic acid. practice. Glyphosate itself is an acid, but it is commonly Moreover, Fe-oxides seem to be a key parameter for glyphosate and aminomethylphosphonic adsorption in soils. This study con- used as a salt, most commonly as isopropylammoniumsalt. firmed previous studies: the analysis showed lower contents of The persistence is typically up to 170 days, with a half- dithionite-soluble and Fe-oxides for the Chernozem, with con- life time of 45-60 days (Peruzzo et al., 2008). Some studies sequently lower adsorption of glyphosate and aminomethylphos- however, show a half-life time of years. The major degrada- phonic as compared with the Cambisol and the Stagnosol. tion product of glyphosate is aminomethylphosphonic acid K e y w o r d s: adsorption, glyphosate, aminomethylphospho- (AMPA), (Gimsing et al., 2004; Locke and Zablotowicz, nic acid, soils 2004; Peruzzo et al., 2008). The glyphosate fate and behaviour in soil are affected INTRODUCTION by different soil factors and processes, but depends also on Soils play an important role in the regulation of conta- interactions between herbicide and soil under the specific minants in ecosystems. Identification and understanding of local conditions (Gimsing et al., 2004; Locke and Zabloto- the mechanisms controlling the fate of chemicals as a source wicz, 2004; Soulas and Lagacherie, 2001). Thus, traces of of environmental contamination, especially in soils and this herbicide have been found in many surface- and ground- water are of major concern. A better understanding for the water systems, (Landry et al., 2005; Peruzzo et al., 2008). organic pollutant behaviour in soils is important for the Consequently, farmers should strive for improved manage- improvement of environmental protection. ment practices in the use and release of these chemicals. This The behaviour of organic contaminants in soils is gene- calls for considering the pesticide type and application rates rally governed by a variety of physical, chemical and biolo- as well as the characteristics of the application site (Soulas gical processes, including sorption-desorption, volatiliza- and Lagacherie, 2001). tion, chemical and biological degradation, uptake by plants, run-off, and leaching (Mamy et al., 2005). One of the key problems for obtaining reliable results Organophosphonates are released into the environment from field samples is to control the possible biodegradation in enormous quantities and, among the non-selective herbi- of glyphosate during storage and preparation of the soil cides, glyphosate is applied at a volume corresponding with samples because the glyphosate content can be influenced about 60% of the global sales (Candela et al., 2007). Glypho- by soil microbes. sate is a polar, highly water-soluble substance that easily The aim of this study was to investigate the behaviour of forms complexes with metals and binds tightly to soil com- glyphosate and AMPA at different soils and time intervals ponents (Ghanem et al., 2007; Gimsing et al., 2004; after field application. Schnurer et al., 2006). *Corresponding author e-mail: [email protected] © 2013 Institute of Agrophysics, Polish Academy of Sciences 204 N. RAMPAZZO et al. MATERIAL AND METHODS Pyhra: – immediately after the Roundup Max application, at 0-2 cm The experiments were carried out at agricultural experi- soil depth; mental fields, where different tillage systems: no-tillage (NT), – 28 days after application at 0-2, 2-5, and 5-10 cm soil direct drill, no plough, with a winter green vegetation cover depth; and maize crop in spring, and conventional tillage (CT), Pixendorf: plough with or without a winter green vegetation cover in – immediately after the Roundup Max application, at 0-2 cm 3 field replications are tested since 2007 (Kirchberg, Styria), soil depth; 1999 (Pyhra and Pixendorf, Lower Austria). – 3 days after application at 0-2 and 2-5 cm soil depth; Three soils under different climatic conditions and fea- – 10 days after application at 0-2, 2-5, and 5-10 cm soil depth. turing different physico-mineral composition were investi- After each soil sampling soil samples were immediately gated: a sandy stagnic Cambisol (WRB, 2006; Nestroy et al., transported to the laboratory in cooling boxes. In the labo- 2000) at Kirchberg (Styria) from tertiary carbonate free sedi- ratory all samples were stored at -18 °C until measurements. ments, a loamy Stagnosol (WRB, 2006; Nestroy et al., 2000) All physical, chemical and mineralogical analyses were from carbonate free sediments (flysch, sandstone) at Pyhra carried out according to the standard methods. (Lower Austria) and a Chernozem (WRB, 2006; Nestroy et al., RESULTS AND DISCUSSION 2000) from loess at Pixendorf (Lower Austria). Moreover, these three soil types were selected because of their contrast- The investigated soils show their distinguished forma- ing physico-chemico-mineralogical parameters eg texture, car- tion through very different textures. The Chernozem shows bonate content, pH-value, and Fe-oxides for a better under- the development from loess with typical high silt content. The Stagnosol has a heterogeneous texture, typical for standing of their influence on the glyphosate behaviour and a loamy soil and the high amount of silt and clay explains the extraction from soils. All three sites were under comparable water stagnation of this soil. The Cambisol is a sandy soil, tillage systems (no-tillage and conventional tillage) in long- with over 50% mass of sand fraction. term experiments (Klik et al., 2010). There is a distinguished difference between the CT- The soils investigated are representative for the main plots and the NT-plots. NT-plots show higher bulk density agricultural regions of Austria, where Cambisols – 50%, Cherno- and lower total porosity than (CT) plots. This compaction is zems – 18%, and Stagnosols cover approximately – 10% of known from the literature and is due to a natural settlement the agricultural land use of Austria (Haslmayr, 2010). of particles free from tillage practices. As a consequence, The Roundup Max application was performed at all there is a loss of coarse pores which leads to a slightly three sites according to the common agricultural practice ie diminished available water capacity (Table 1). 4 l Roundup Max (450 g glyphosate /l Roundup Max) were The silty Chernozem is slightly alkaline with a medium dissolved in 200 l of water and applied per ha (2 % herbicide carbonate content. The siliceous Stagnosol and Cambisol solution). This corresponds to an application of 1 800 g gly- are weakly acidic, according to their formation conditions. phosate ha-1 or 180 mg glyphosate m-2. The application was The contents of soil organic matter decrease with soil depth carried out at sunny and not windy weather at the NT-plots. (Table 2). Soil bulk samples from all plots (NT and CT) were taken Pedogenic Fe-(Al)-oxides are important indicators for for physico-chemico-mineralogical analysis at each site at eg weathering intensity and redox processes in soils. They two soil depths (0-5 and 5-20 cm), collected from 10 diffe- play also a major role as absorbers for glyphosate in soils. rent points/field replication. The samples were air-dried and The dithionite-soluble Fe(Fed) indicates the total amount of sieved at 2 mm size (fine earth). Moreover, for further phy- pedogenic formed Fe-oxides, that means organically bound, sical analysis undisturbed samples (cylinders with 200 cm3) amorphous and well crystallized. This Fe-extraction does were taken separated from each NT and CT field replication not allow any conclusion about the type of Fe-oxide (goet- at 5-15 cm soil depth each in 5 repetitions. hite is however the most relevant Fe-oxide in Central Europe). In order to investigate the fate of glyphosate and AMPA The Chernozem features a low content, the Stagnosol in depth and time after Roundup Max application, soil bulk a medium content and the Cambisol a high content of Fe- samples were taken at different time intervals after applica- oxides (Table 3). From this, the expected sorption capacity tion at 10 points within each NT-field replication (pooled for glyphosate and AMPA increases respectively from the than to one sample per site) as follows: Chernozem, over the Stagnosol to the higher weathered Kirchberg: Cambisol. All sites show a low Fe-oxides/ dithionite-soluble – immediately after the Roundup Max application, at 0-2 cm Fe(Feo/Fed) ratio which indicates that in all soils investi- soil depth; gated the most relevant amount of pedogenic Fe-oxides is – 3 days after application at 0-2 and 2-5 cm soil depth; well cristallized (Table