Reducing cadmium accumulation and increasing grain yield with proper timing of flood irrigation in the second season of ratoon rice

Abstract

Context or problemThe second season of ratoon rice (ratoon crop, RC) exhibits a high risk of cadmium (Cd) contamination in grains, requiring effective irrigation management strategies to reduce its grain Cd concentration. Objective or research questionThis study aimed to determine the crucial growing period for Cd accumulation and provide irrigation recommendations for reducing grain Cd concentrations with limited water input in the ratoon season. MethodsA two-year field experiment was conducted in Hubei province, central China. The entire growth duration of RC was divided into three short periods: from harvest of the main crop (HM) to initial heading of RC (IH), from IH to full heading of RC (FH), and from FH to maturity of RC (MR). During each growth period of RC, two water regimes (flooded and rainfed) were established. Therefore, there were a total of eight water treatment combinations in this experiment, using a randomized complete block design. Two hybrid varieties were planted in this study. ResultsAcross years, varieties and treatments, the grain Cd concentration of RC ranged from 27.8 to 314.1 µg kg−1, with 37.5% of rice samples exceeding the national food safety standard for Cd (200 µg kg−1). RC grown under continuous flooding conditions produced the lowest grain Cd concentration and highest grain yield. Compared with rainfed conditions, maintaining flooded conditions from HM to IH, from IH to FH, and from FH to MR resulted in decreases of 28.4%, 62.7%, and 12.0% in grain Cd concentration and decreases of 25.5%, 49.9%, and 16.3% in total Cd accumulation at maturity, respectively. RC took up the most Cd during the period from IH to FH under rainfed conditions; however, maintaining flooded conditions reduced Cd uptake by 95.4% during this period. Moreover, flooding from IH to FH had the most positive impact on the grain yield of RC, with an increase of 8.1% compared with rainfed conditions. ConclusionsMaintaining flooded conditions from initial to full heading for 15–18 days was not only effective in reducing grain Cd concentration but also beneficial for improving grain yield in the ratoon season. Implications and significanceThis study clarified the effects of water management during different growing periods on Cd accumulation and grain yield in the ratoon season. We emphasized the necessity of flooding during heading period to control Cd accumulation in RC grains, especially in areas with limited water resources and high soil Cd concentration.