Olfa Gharsallah

Traditional surface irrigation remains the most widespread practice in the Po Plain, supporting one of Italy’s most productive agricultural regions. The system relies on large river withdrawals that are distributed through an extensive network of unlined, often centuries-old canals supplying agricultural fields. Although frequently criticized for inefficiency, surface irrigation generates hydrological effects that extend well beyond direct crop water supply. Indeed, percolation from irrigated soils and seepage from open channels contribute substantially to groundwater recharge, thereby moderating seasonal fluctuations in surface water availability and alleviating drought stress.Despite its hydrological relevance, irrigation-induced groundwater recharge in the Po Plain remains poorly quantified. The region exhibits a highly complex hydrological system, dominated by strong surface water–groundwater interactions, while detailed data on irrigation practices, water deliveries, land use information and dynamic shallow water table fluctuations are limited. Robust estimates of the contribution of traditional irrigation to aquifer replenishment are therefore essential for sustainable water resources management, particularly in case of relevant climatic variability.Within the MidAS-Po project, a comprehensive methodological framework was developed to quantify groundwater recharge across the entire Po Plain, accounting for contributions from both percolation from irrigated fields and seepage from unlined irrigation channels. The approach integrates two components. First, the distributed agro-hydrological model IdrAgra was applied to simulate the daily soil water balance and estimate percolation from agricultural soils. Second, recharge associated with canal seepage was assessed using a simplified methodology based on the estimation of the channel distribution efficiency.The results indicate that recharge of aquifers induced by traditional surface irrigation accounts for between 50% and 65% of total recharge. The lower percentage is obtained when considering the role of the saturated soil zone in limiting percolation flows, and allowing root uptake from the capillary fringe in those areas of the Po Plain, where the aquifer is shallow; the higher percentage reflects the results of a simulation in which free drainage conditions were assumed at the base of the rooted soil volume. Given the considerable limitations in the knowledge of the spatial distribution of the phreatic aquifer depth, it is currently impossible to say which of the two estimates is more accurate.These findings challenge conventional views on traditional irrigation efficiency, highlighting that water “losses” from irrigated fields and open channels are not merely waste but represent an important source of aquifer recharge. Further refinements are needed to improve these estimates. In particular, shallow water table depth data are currently not sufficiently accurate in terms of spatial resolution and are inadequate for capturing the seasonal and inter-annual fluctuations. Enhanced data on shallow water table depth would strengthen the model performance, improving estimates of crop irrigation requirements and of groundwater recharge.

The Po Valley, Italy's largest and most economically significant region, heavily relies on intensive irrigation to sustain its very productive agriculture and meet the demand of a variety of high-value food productions. Historically, the region's agricultural success has been driven by widespread traditional surface irrigation systems, which primarily draw water from rivers and deliver it to fields through an extensive network of irrigation canals. These systems, that in many areas have been operational for centuries, not only enhance agricultural productivity but also contribute to groundwater recharge, helping to mitigate river droughts and seasonal fluctuations in surface water availability. In recent years, however, declining surface water availability and increasing reliance on groundwater extraction have already been observed, because of a higher variability of summer precipitation and decreasing winter snow accumulation in the Alps caused by climate change. Consequently, accurately estimating groundwater recharge from irrigation excess has become crucial. Despite its importance, the impact of irrigation on groundwater recharge across the Po Valley remains poorly investigated. This is mainly due to the complexity of the region's hydrological systems characterized by strong interactions between groundwater and surface water, and to the lack of reliable data covering the entire Po Valley.In the context of MidAS-Po project, a methodological approach has been developed for the preliminary estimation of groundwater recharge through percolation from irrigated areas and seepage from irrigation channels over the whole Po Valley.This approach involves two main steps. First, the application of a distributed agro-hydrological model, IdrAgra-Po, simulating daily soil water balance terms, including percolation from the agricultural soil layer (1 meter deep) in irrigated fields. The model was implemented over the period 2010–2022, with a spatial resolution of 0.25 km², and incorporates several input datasets: i) agro-meteorological conditions from the E-OBS dataset, produced by the Copernicus Land Monitoring Service of the European Environment Agency; ii) soil hydro-pedological data sourced from four regional databases, processed and harmonized over the study area; iii) land use data provided by the CORINE project and integrated with local information; and iv) depth of the shallow groundwater table. The second step is the estimation of groundwater recharge due to seepage from the irrigation network using a simplified methodology that relies on the data of the national agricultural information system SIGRIAN. This approach estimates channel seepage as the ratio between the measured water volumes allocated upstream of the irrigation districts into which SIGRIAN splits the Po Valley and the irrigation requirements determined by the IdrAgra-Po model for the same districts.The resulting preliminary estimate of groundwater recharge linked to irrigation practices represents a significant step toward understanding the role of irrigation in the aquifer recharge in Po Valley. However, further investigations should be conducted to improve the quality of the input data, mainly, information on local irrigation methods and practices, land use and irrigation volumes diverted from rivers and withdrawn from aquifers.Acknowledgment This contribution is presented in the framework of the MidAS-Po project, funded by Italy's Development and Cohesion Fund - FSC 2014-2020.

Rice is the world's most important food crop, as it is a staple food for more than half of the world's population, and the global demand for rice is expected to increase. More than 1,000,000 hectares in the Mediterranean basin are devoted to rice cultivation. The most important producing countries are Italy (IT) and Spain (SP) in Europe (over 310,000 ha), and Egypt (EG) and Turkey (TR) among non-EU countries (over 600,000 ha). In the Mediterranean region, rice production is of great socio-economic and environmental importance, as rice is often a crucial product for internal consumption and export, especially in Egypt, where it is considered strategic for food security. Despite of this, the peculiar flooding conditions in which rice is traditionally grown lead to the use of huge water volumes, as well as to the potential release of greenhouse gases and pesticides into the environment. For this reason, the introduction of water-saving irrigation strategies could reduce water consumption and decrease the harmful environmental impacts associated with rice flooding, while maintaining yield and rice grain quality.In the context of the MEDWATERICE project (https://www.medwaterice.org/; PRIMA-2018), alternative irrigation methods to WFL were tested in case studies implemented in five Mediterranean countries (Italy, Spain, Portugal, Turkey, Egypt). Irrigation strategies for each CS were selected with the support of local Stake-Holder groups and applied in experimental fields measuring/estimating all the water balance terms on a daily basis. Wet seeding and alternate wetting and drying (AWD), dry seeding and delayed flooding (DFL), reduction of inlet/outlet discharges (WIR), a better control of ponding water level through automated gates (DFL-aut), hybrid irrigation (HYBRID), sprinkler irrigation (SPRINKLER), surface drip (DRIP) and subsurface drip irrigation (SDI) were implemented for at least two years in the period 2019-2021 alongside the traditional WFL, to investigate their environmental and economic sustainability and social acceptability.

The study presents a bibliometric analysis of scientific literature on alternate wetting and drying (AWD) as a water-saving irrigation practice for rice cultivation. Data were collected from the Web of Science, resulting in a database of 439 articles written by 2574 authors in 167 journals. The study reveals the growing importance of AWD in publications from the 90s to mid-2022, with fast growth and reaching its peak in the last 5 years, suggesting that the full potential of AWD remains yet to be realised and explored. Most papers are produced in oriental countries, except the USA and Australia. The trend of keywords in the research on AWD reveals a persistence of certain themes throughout the years while simultaneously showcasing a clear evolution of the topics being addressed. In addition to optimising productivity and agricultural yields, research now encompasses environmental issues and human and crop health, reflecting a broader trend in agriculture and research towards sustainable and environmentally responsible practices. This analysis provides insights into the development and direction of research in AWD, emphasising the need for future research to address the emerging concerns of the impact of AWD on the environment, human and crop health, and economic profitability of AWD adoption.

Italy is the Europe’s leading rice producer, with over half of total European production. The main rice area is in the north-western part of the country (Lombardy and Piedmont regions). In this area, irrigation of rice has been traditionally carried out by flooding; the introduction of alternative water-saving irrigation strategies could reduce water consumption, but their overall environmental and economic sustainability, as well as their social acceptability, should be investigated.An experimental platform was set up in the core of the Italian rice district (Lomellina, PV) to compare different rice irrigation management options: wet seeding and traditional flooding (WFL), dry seeding and delayed flooding (DFL), wet seeding and alternated wetting and drying (AWD). Six plots of about 20 m x 80 m each were set-up, with two replicates for each irrigation option. One out of two replicates for each option was instrumented with: water inflow and outflow meters, set of piezometers, set of tensiometers and water tubes for the irrigation management in the AWD plots. Proper agronomic practices were adopted for the three management options. Periodic measurements of crop biometric parameters (LAI, crop height, crop rooting depth) were performed and rice grain yields and quality (As and Cd in the grain) were determined. Data measured in the field, together with those provided by the farmer, concerning the agronomic inputs and the economic costs incurred for the three irrigation options, were used to assess their economic and environmental sustainability through a set of quantitative indicators. Finally, through interviews with rice growers of the area, barriers to the adoption of the AWD technique were assessed and ways of overcoming them identified. In order to support water management decisions and policies, data collected at the farm level are extrapolated to the irrigation district level through a semi-distributed agro-hydrological model, used to compare the overall irrigation efficiency achieved implementing AWD when compared to WFL.

The intensification of agricultural production is connected to the increased use of fertilizers, pesticides, irrigation water, and energy. Among all cropping systems, rice cultivation is considered to be one of the most significant sources of environmental harm due to the flooding conditions in which rice normally grows; at the same time, rice has important economic and social implications, especially in areas where it is a staple food. In the last 20 years, sustainable development of agricultural production has become a priority for scientific research and policy programs. Several studies proposed methodological frameworks to assess the impacts of different management practices adopted in agro-ecosystems and to identify strategies to mitigate the negative effects of agricultural intensification. Such methodologies are based on the use of particular indicators, which are increasingly seen as crucial tools in impact assessment studies and for decision making. This paper aims to review and analyze the most significant methodological frameworks developed to assess the sustainability of agricultural production systems, with a particular focus on rice cultivation. The analysis includes highlighting which dimensions of sustainability (economic, environmental, social, and governance) are covered by each method and identifying which indicators are used to describe the different dimensions. The spatial scale of the application of the indicators, their typology, the data needed for their implementation, and the criteria for formulating the overall sustainability judgment were then examined. The analysis highlighted the scarce availability of clear operational data for the calculation of the indicators and the often-limited involvement of stakeholders in the development and implementation of the methodologies. The exceptions to these limitations are represented by a few methodologies developed under the umbrella of important international organizations to promote sustainability and research efficiency in specific agricultural production systems, such as the SRP (sustainable rice platform) for rice. Finally, the analysis shows that there is a need to develop methodologies that are applicable not only to an individual farm or group of farms, but also at larger spatial scales (district, watershed, region), which are often those of greatest interest to decision makers.