How water amounts and management options drive Irrigation Water Productivity of rice : a multivariate analysis based on field experiment data

Rice cultivation is globally hampered by several conditions, which urge farmers to maintain adequate production levels while properly managing irrigation water. This has noticeable repercussions on the efficient use of the resource and on water productivity. Nonetheless, more often, this latter topic is addressed by estimating the respective values, without deeply investigating the possible causes behind such discrepancies. The main objective of this paper is to overcome such limitations, by (i) providing a comprehensive and updated overview of Irrigation Water Productivity (IWP) for rice, and (ii) exploring the role of irrigation water in determining IWP value. The analysis of experimental data collected from 51 studies reveals IWP to vary between 0.09 and 8.10 kg m-3, with mean and median values of 1.36 and 0.85 kg m-3 respectively; moreover, a non-linear relationship between irrigation water amounts and IWP (r2= 0.81) is depicted. Further on, data are analyzed using an econometric approach. Specifically, a multivariate linear regression model is used to shed light on the joint contribution of water inputs, regime and irrigation method to productivity. This demonstrates the significant roles of irrigation (B = 1.006) and rainfall (B = 0.062) amounts, while aerobic regime and irrigation method is proved to be a further key driver (B = -0.305). Such results enable identifying the elements to be enforced, if increasing IWP for rice is the prime objective. Finally, some implications are derived for water policy and the connections with weather-climatic and environmental conditions that are globally affecting the availability of water in agriculture.