The role of water management and environmental factors on field irrigation requirements and water productivity of rice

Rice cultivation requires a significant share of irrigation water, mostly because of the practice of continuous flooding; therefore, interest for alternative water managements is increasing. The paper presents results of a 2-year experiment in Northern Italy comparing three rice water managements: Water seeding-continuous FLooding (WFL), Dry seeding-delayed FLooding (DFL) and Dry seeding-intermittent IRrigation (DIR). The main objective was to assess the effects of water regimes on the agroecosystem as a whole (from water use and yield components to nutrient dynamics, etc.). This paper is focussed on water use aspects with the aim of: (1) comparing and discussing water balance terms, water use efficiencies and water productivities; (2) analysing percolation fluxes of flooded treatments (WFL and DFL); and (3) discussing interannual variations of paddy irrigation requirements due to environmental factors. Net irrigation requirements of WFL ranged between 1500 and 3000 mm in the two seasons, while DFL and DIR determined average reductions by 20 and 60 %. On the other hand, WFL provided an average yield of 10.2 t ha(-1), which decreased by 3 and 28 % in DFL and DIR, respectively. Between-years variability can be attributed to environmental factors including groundwater levels and soil responses to abiotic and biotic factors. Percolations of flooded treatments showed a strong correlation with groundwater levels, especially during the first part of the season (R (2) 0.90 and 0.95, respectively). Data analysis highlighted complex subsurface water dynamics dependent on groundwater levels and influenced by soil characteristics.