Imazamox loads in irrigation tailwaters and percolation fluxes from paddy fields in northern Italy

Abstract

Italy is the Europe leading rice producer, with more than half of the total production and a high quality level. Although the main function of paddy areas is the production of rice, these complex agro-ecosystems are linked to issues of great concern such as the freshwater conservation in terms of both water consumption and water quality. An intensive experimental activity was started in 2015, in the framework of the WATPAD project (Fondazione Cariplo, Grant No 2014-1260), to investigate the water balance terms and the water quality impacts on surface water and groundwater of four paddy fields located in Lomellina (western part of the Po river plain). A different irrigation management was adopted for the four paddies: wet seeding and continuous flooding (WFL) was applied within two fields, while dry-seeding and delayed flooding was adopted for the other two paddies. The four fields were instrumented with devices measuring irrigation inflows and outflows, water level in the fields, soil moisture and groundwater depths. Additionally, in each field, three couples of porous cups were installed at depths of 25 and 60 cm. Water samples of irrigation inflows and outflows, water in porous cups, and groundwater were collected along the agricultural season (26 sampling dates in 2015). Water samples were analyzed for various compounds, including the herbicide Imazamox and its degradation products. The contemporaneous quantification of water fluxes and Imazamox concentrations allowed the determination of Imazamox loads released in surface waters and groundwater along the agricultural season for each field. The main findings, which will be discussed in the poster, are the following: i) most of the Imazamox loads leave the paddies through percolation; consequently, fields characterized by more permeable soils contribute more to Imazamox concentrations in groundwater; ii) Imazamox loads in surface outflows are modest, as the half-life of Imazamox in surface waters reached by solar radiation is very low; iii) from the data available to date (agricultural season 2015) Imazamox concentrations in porous cups may seem to be influenced from the concomitant use of fertilizer products. In particular, it is known from the literature that the degradation of Imazamox is pH and oxygen dependent; thus, the use of fertilizers having an effect on these water parameters could influence the Imazamox persistence in the field, favoring its transport to groundwater; iv) more research is needed to investigate the eventual field interaction between Imazamox and the use of fertilizers, as well as to monitor the environmental fate of Imazamox degradation products