ice (Oryza sativa), the most important staple crop in South and Southeast Asia is commonly grown by transplanting seedlings into puddled soil. Although puddled transplanted rice (PTR) has several benefits, particularly in terms of weed control and water conservation, it is highly water-labour and energy intensive. PTR is also a major greenhouse gas (GHG) emitter, contributing up to 20% of total global methane emissions. The drudgery associated with manual transplanting (a job largely done by female farmers) is deleterious for human health. The sustainability of PTR method of rice cultivation and rice-based cropping systems in Asia is at risk with the predicted water-labor shortages, increased cost of irrigation, expensive labor, and change in rainfall pattern/distribution. Increase in agricultural productivity through a combination of improved water control, proper land management, better agronomic practices, introduction of water saving technologies and varieties, identification of ideal plant type, mechanization, development of new data sources, superior models, powerful data analysis tools/techniques, with the design of adaptive management approaches can help in responding effectively to changing and uncertain conditions.
In the face of global water scarcity and escalating labour rates, when the future of rice production is under threat and innovative solutions to increase water productivity are being developed Dry Direct Seeded Rice (DDSR) offers a viable alternative to PTR. The practice of growing rice into dry soil reduces the need for water in land preparation and also allows farmers to plant rice crops before the rains of the wet season arrive to utilize rainfall to support crop growth rather than land preparation activities. Early planting can also help rice to escape drought, which generally occurs late in the wet season in rainfed ecosystem.The case study of United States, Malaysia, and Sri Lanka where more than 90% of the rice has been direct-seeded for the past few decades provide important lessons for the countries that are moving toward DSR. Now a day’s direct seeded rice cultivation practices are getting more popularity in South Asia (India, Nepal, Bangladesh), South East Asia (Philippines, Cambodia, Vietnam, Laos and Myanmar) and to some extent in West Africa. Lack of suitable rice varieties for DDSR has been a major constraint for adoption in these areas. A successful transition of rice cultivation from PTR to DDSR will rely on the development of new rice varieties possessing better adaptability to DDSR.
Mechanized DDSR method of rice cultivation have been estimated to provide a potential rice yield increase of 0.5 t/ha, irrigation water savings of 40 cm/ha, labour savings of 25 person-days/ha, energy savings of 1,500 MJ/ha, a reduction of GHG emissions of 1,500 kg CO2 equivalent/ha and increased net economic return of USD 50/ha in most of the rice-growing countries (Kumar and Ladha, 2011). DDSR method of rice cultivation looks to be more adapted to future climate change process and shall help develop a sustainable rice-based cropping pattern. DDSR accounts for less than a quarter of global rice production but it is becoming popular and is likely to be widely practiced in many areas where it has been shown to provide economic, social and environmental advantages over PTR. To obtain higher yield under DDSR, a suitable plant type with combination of traits in a variety that are different from traits present in rice plant type suitable for PTR are needed.
The studies conducted at CCS Haryana Agricultural University, Hisar and at International Rice Research Institute (IRRI) have identified the donors and the genetic regions associated with increased nutrient uptake under dry direct seeded situation, early vigor, nodal root, total root length, root volume, root dry weight, root hair length, root hair density (Sandhu et al. 2013; Sandhu et al. 2015) as well as for plasticity for root dry weight, root length density, % lateral roots (Sandhu et al. 2016).
Development of fast uniform emerging, nutrient efficient, biotic resistance and high yielding dry direct seeded rice varieties with appropriate climate smart plant type will be a sustainable solution to the water-labor scarcity, drudgery, global warming and future unpredicted environment. Development of eco-friendly genotypes with stable yield across different environments will be increasingly desirable for rice farmers in the face of climate change-related variability. Modernization employing mechanistic understanding, new traits, donors, genes and genomic techniques from research platform will contribute to future transformation of existing puddled transplanted system of rice cultivation.
References: Sandhu N, Jain S, Kumar A,Mehla BS, Jain R (2013) Genetic variation, linkage mapping of QTL andcorrelation studies for yield, root, and agronomic traits for aerobic adaptation. BMC Genet 14:104–119. Sandhu N, Torres R, Sta Cruz MT,Maturan PC, JainR, Kumar A, Henry A (2015) Traits and QTLs fordevelopment of dry direct seeded rainfed rice varieties J Exp Bot 66:225–244 Sandhu N, Raman KA, Torres RO, Audebert A, Dardou A, Kumar A, Henry A (2016) Rice root architectural plasticity traits and genetic regions foradaptability to variable cultivation and stress conditions. Plant Physiol 171:2562–2576. Kumar V, Ladha JK (2011) Direct seeding of rice: recent developmentsand future research needs. AdvAgron111:297–413