Alternate wetting and drying irrigation with field aged biochar may enhance water and rice productivity

Abstract

Rice is traditionally cultivated worldwide under continuous flooding irrigation. However, in Mediterranean environments, there has recently been a decline in the area of rice cultivation in several producing regions where water supplies for this crop cannot always be guaranteed. Therefore, it is necessary to identify alternative crop management strategies that improve water-use efficiency in order to ensure the sustainability of rice production. It has been postulated that rice production under alternate wetting and drying (AWD) irrigation requires less water than flooding. However, the effects of the AWD system on rice yield components remain unclear, with different trends observed. It has been suggested that the soil properties are a crucial factor in this regard. In fact, drops in rice yields under AWD have been attributed to the low soil organic matter content. Consequently, the incorporation of organic amendments could offset this organic matter deficit, and the subsequent enhancement in rice productivity might also ensure its sustainability in areas where water availability is scarce. This study is the first to analyse how the soils properties, rice yields components, and water productivity were influenced by fresh and field aged biochar applied to rice soils under conventional flooding and AWD using two-threshold (mild and severe). The results showed that the transition from flood management to AWD management has had a significant impact on soil properties and rice yields, though this was dependent on the threshold. Consequently, yield losses occurred under severe AWD conditions in comparison to the flooded systems. Nevertheless, the use of holm oak biochar was found to enhance rice yields under AWD systems, particularly under severe conditions and following the field ageing process. Thus, the combined use of biochar and AWD may be a sustainable strategy to enhance water productivity, which is one of the main objectives in the rice crop.