Improvement of submergence tolerance in rice through efficient application of potassium under submergence-prone rainfed ecology of Indo-Gangetic Plain Sharad Kumar Dwivedi A,B , Santosh Kumar A , Narayan Bhakta A , Shishir Kant Singh A , Karnena Koteswara Rao A , Janki Sharan Mishra A and Anil Kumar Singh A A Indian Council of Agricultural Research – Research Complex for Eastern Region, Patna, Bihar- 800 014, India. B Corresponding author. Email: sharad.dwivedi9736@gmail.com Abstract. Potassium (K) is one of the limiting factors that negatively influenced rice growth and yield in submergence- prone soils. We conducted an experiment during the wet season of 2014–15 to achieve optimal doses of K and understand the effect of K application on submerged rice in terms of survival, chlorophyll content, non-structural carbohydrates (NSC), anti-oxidant activities and yield. Results revealed that chlorophyll and NSC content were significantly (P  0.05) lower whereas the activity of anti-oxidants (catalase, superoxide dismutase and total peroxidase) were significantly (P  0.05) higher after submergence compared with pre-submergence. Further, application of K at a higher basal dose (40 kg ha –1 ) was more beneficial to improve survival after de-submergence by maintaining NSC, chlorophyll content and higher activity of anti-oxidants with lower level of lipid peroxidation. Furthermore, results showed superiority of the treatments having application of higher doses with one foliar spray (T9–40 kg K 2 O ha –1 (basal) + one foliar spray at 0.5% K at panicle initiation (PI) stage) for grain yield. We conclude that application of a higher dose of K with one foliar application at PI stage is more beneficial to enhance plant survival, better recovery and yield gain of rice during complete submergence. Additional keywords: anti-oxidative defence system, foliar spray, K management, physiological traits, split application. Received 1 October 2016, accepted 19 May 2017, published online 21 June 2017 Introduction Rice (Oryza sativa L.) is the staple food of more than three billion people in the world; most of them live in Asia (IRRI 2009). Approximately one fourth of the global rice production area (~40 million ha) is located in rainfed lowlands of the humid and subhumid tropics of south and south-east Asia and Africa. Rainfed lowlands constitute highly fragile ecosystems that are prone to flash-flooding with an average productivity of only 1.2 t ha –1 in normal years and ~0.5 t ha –1 in case of submergence (Sarkar et al. 2006). Eastern India alone has ~10 million ha of rice lands affected by flash-flooding and complete submergence. Flooding, therefore, is a major constraint to increasing rice yield in eastern India where transient submergence (short-term floods) is very common (Ram et al. 2002). Lowland rice is typically cultivated in paddies of 5–25 cm of standing water, which are highly vulnerable to monsoon flash floods of 50 cm or more that can rapidly and completely submerge plants. The flash-flood situations are extremely unpredictable and mostly of relatively short duration (7–14 days), leading to partial or complete failure of crop (Setter et al. 1997). The optimal potential of an improved variety can only be harnessed when layered with appropriate management practices. Although the rice plant is well adapted to aquatic environments, it is unable to survive if completely submerged in water for an extended period. During recent years, the submergence-tolerance gene SUB1 was identified, fine-mapped and transferred into several mega-varieties of rice in South Asia. Swarna-Sub1 – a product of marker-assisted backcross of Swarna – has performed well under submergence conditions. Considering this scenario, the elite variety Swarna-Sub1 was included in the present study. Environmental stresses reduce rice growth and severely affect the seedling biomass, photosynthesis, stomatal conductance, plant water relations and starch metabolism (Farooq et al. 2009). Potassium in rice-producing soils is one of the limiting factors influencing rice yield (Yang et al. 2003). There is a considerable decrease in available K due to increased cropping intensity and lower K application rates (Zhang et al. 2004). The regulation of K + homeostasis is essential for plant adaptation to biotic and abiotic stresses. Under flooded conditions, K + is leaked from flooded roots, which has a detrimental effect on overall plant nutrition and is mainly responsible for K + deficiency in crops grown in waterlogged soils (Marschner 1995; Shabala 2011). Thus, avoiding K + loss during hypoxia or anoxia conditions is the key mechanism for resistance in plants under submergence conditions (Pang et al. 2006; Mugnai et al. 2011; Gautam et al. 2016). This adaptation is associated with the wide range of functions in which K + participates (Demidchik 2014; Shabala and Pottosin 2014). However, very little work has investigated CSIRO PUBLISHING Functional Plant Biology http://dx.doi.org/10.1071/FP17054 Journal compilation Ó CSIRO 2017 www.publish.csiro.au/journals/fpb