, 55 % lower compared to CF30, while no differences in nitrous oxide emissions were observed between treatments (p > 0.05). No yield differences between irrigation systems were observed in two of the rice seasons (p > 0.05) while AWDI promoted yield reduction in one of the seasons (p < 0.05). When rice yield and greenhouse gases (GHG) emissions were considered together, the AWDI irrigation system allowed for lower yield-scaled total global warming potential (GWP). Higher irrigation water productivity was achieved under AWDI in two of the three rice seasons. These findings suggest that AWDI could be an option for reducing GHG emissions and increasing irrigation water productivity. However, AWDI may compromise grain yield in certain years, reflecting the importance of the need for fine tuning of this irrigation strategy and an assessment of the overall tradeoff between relationships in order to promote its adoption by farmers.

The environmental impact of rice agriculture is poorly studied in developing countries, mainly, due to limitations of the analytical capacity. Here we report the development of a clomazone ELISA as a fast and cost-effective tool to monitor the dissipation of this herbicide along the harvest. Antibodies were prepared using different strategies of hapten conjugation, and the best hapten/antibody pair was selected. It proved to be a reliable tool to measure the herbicide in the 2.0-20 ng/mL range in field samples, with excellent correlation with HPLC results. The assay was used to study the dissipation of the herbicide in floodwater of experimental rice paddies in Uruguay. Large differences in the residual amount of herbicide were observed depending on the flooding practices. Due to its robustness and simplicity, the assay may be useful to delineate and monitor management practices that can contribute to minimizing the release of the herbicide in the environment.

Environmental impact and sustainability of agricultural systems and management practices leading to climate change mitigation are one of the most relevant issues to agricultural production nowadays. Mitigation is the process of reducing emissions or enhancing sinks of greenhouse gases (GHG), to limit global warming potential and restrict future climate change. The most relevant GHG are Carbon dioxide (CO2), Methane (CH4) and Nitrous Oxide (N2O). The steady increase of its concentrations in the atmosphere over several decades has led to enhance global warming. CH4 and N2O are the most relevant GHG emitted mainly in the agricultural sector. It is well known that water management has great impact on GHG emissions from rice paddy fields. One of the most important tools for rice crop production and mitigation of CH4 emission is the controlled irrigation. However, it could result in a N2O emission increase and reduced rice yields. For these reasons, it is remarkably important to assess the tradeoff relationship between both GHG and the effect on rice productivity. A 3 year field experiment with two different irrigation systems was set at southeast of Uruguay. Conventional water management (continuous flooding after 30 days of emergence, CF30) and an alternative irrigation system (controlled deficit irrigation allowing wetting and drying, AWDI) were compared. The objective was to study the effect of water management on GHG emission, water productivity and rice yields in order to identify strategies for further progress in sustainable intensification of Uruguayan rice. Results showed that mean cumulative CH4 emission values for AWDI were 55% lower than CF30 systems; on the other hand, there were no significant differences in N2O emission among systems. Significant yield differences were not observed in two of the rice seasons, while AWDI recorded a significant yield reduction in one of them. Total irrigation water applied and irrigation water productivity did not showed differences in two of the rice seasons, while CF30 reported a higher amount of water applied and lower water productivity in one of the seasons. It can be concluded that AWDI could be an option to enhance water productivity and GHG emission mitigation. However, grain yield can be compromised in AWDI systems. The adoption of these technology is based on the indispensable assess of an overall tradeoff between the risk of possible yield losses, total water used and GHG emissions.

Soil organic carbon (SOC) is a key soil quality indicator for cropping systems sustainability. We evaluated 20 yrs. soil use intensity effects on SOC (0-5 cm and 5-15 cm depth) in a 72 ha no-till crop-pasture rotation experiment (33°:15’36"S, 54°:29’26"W, 60-m elevation) in Treinta y Tres, Uruguay (Abruptic Argiaquolls and Oxiaquic Vertic Argiudolls). Treatments between 1995-2005 were: Continuous cropping (CC) of ryegrass (Lolium multiflorum Lam. or oat Avena sp. in winter and sorghum (Sorghum bicolor L.) or foxtail millet (Setaria italica) in summer; 2) Short Rotation (SR): two years idem CC and two years pasture of red clover (Trifolium pretense L.) and Holcus lanatus L.; 3) Long Rotation (LR) two years idem CC and four years pasture of tall fescue (Festuca arundinacea L.), white clover (Trifolium repens L.) and birdsfoot trefoil (Lotus corniculatus L.); 4) Permanent Pasture (PP): natural pasture overseeded with legumes used in RL. Since 2005 until now, grain crops substituted forage crops in the «cropping phase» of all rotations (CC, SR, LR), maintaining without modifications the pasture phase of them. Grain cropping sequence was: Oat (Avena sativa L.), Sorghum bicolor (L.), black oat (Avena sp., as a winter cover crop), soybean (Glycine max L.) and wheat (Triticum aestivum). After 20 years, significant SOC differences (0-5 cm) were found between rotations. Continuous cropping decreased SOC by 16%, 18%, 31% compared to SR (25.55 g kg-1), LR (26.17 g kg-1) and PP (31.32 g kg-1), respectively. Although no SOC differences were found between rotations that include perennial pastures (SR and LR), both had 18% lower SOC than PP. A trend of SOC decrease (12%) was observed also in PP compared to the original situation that existed at the beginning of the experiment (natural pasture 35.25 g kg-1). No SOC differences were found in the 5-15 cm depth between treatments that included pastures. However, there was an average SOC increase of 14% in these treatments (13.34 g kg-1) compared to CC. The aggregate of data suggest that, even under no-till, continuous cropping reduced SOC compared with cropping systems that include some proportion of pastures in the rotation. For undisturbed fragile soils incorporated to grain production, like those prevalent in 1 million ha in Eastern Uruguay, the inclusion of perennial pastures in the rotations is critical for soil conservation and mitigation of SOC losses in cropping systems.