Rice irrigation in northern Italy: field and district scale evaluations

The majority of rice produced in the European Union is grown in Italy, where the crop requires relevant amounts of irrigation water for the continuous flooding (CF) of rice fields. In this area some water saving technologies such as delayed flooding (DF) and flush irrigation (FI) are spreading. To improve the understanding of water management issues in rice systems, the paper presents the results of both field scale and district scale studies on water requirements of rice grown with water techniques. At the field scale, we compared water balance terms and water performance indicators of CF, DF and FI rice over two growing seasons (2012 and 2013), whereas, at the district scale, we adopted a modelling approach to estimate the effects of a widespread conversion from CF to FI on the water requirements of the district. Results obtained from field-scale experiments suggested that water inputs to rice can be reduced by 20% and 60% on average CF is replaced by DF and FI respectively, but at the expense of lower yields, especially in case of FI (-3% and -28% for DF and FI, respectively). Moreover, a great difference in irrigation requirements CF and DF between the two subsequent seasons was observed. Such inter-annual variability was attributed to the combined effects of environmental factors (e.g. groundwater depth, changes in soil structure, etc.). With a focus on the district scale, the study highlighted the importance of carefully evaluating the effects of widespread changes in the water management of rice, since CF maintain a shallow water table which provides a direct water supply to other crops through the capillary rise. In fact, a complete conversion from CF to FI in the district resulted in a reduction of rice irrigation requirements by 60%, but it determined an increase of maize requirements by about 50% due to the decline of the groundwater depth