Effect of Water-saving Technologies on Growth, Yield, and Water-saving Potential of Lowland Rice

Alternative methods of rice production that use fewer freshwater inputs are crucial for sustainable rice production in the context of decreasing irrigation water availability, which may further exacerbate due to climate change. The direct seeding (DS) method of cultivation (either dry or wet) and alternate wetting and drying (AWD) are among such ways, which could contribute to decreasing irrigation water inputs in rice production without a considerable yield penalty, thus increasing water productivity. The objective of the study was to investigate the performance of a popular, lowland, Thai rice variety (Pathumthani 1) under different cultivation methods subjected to different threshold levels of AWD. The treatments involved three cultivation methods (dry direct seeding [DDS], wet direct seeding [WDS], and transplanting [TP]) and four soil moisture levels of 0, ?5, ?15, and ?30 kPa, maintained through a permanently installed tensiometer. The growth, yield components, grain yield, and water-saving potential of rice under different cultivation methods and soil moisture levels were determined. There were more unfilled grains at ?30 kPa under the DDS method. At the severe moisture stress of ?30 kPa, the DDS method resulted in a 24% higher grain yield than did the TP method, whereas the difference in grain yield between WDS and TP was nonsignificant at moisture levels of 0, ?15, and ?30 kPa. The highest water-saving potential of 62% compared with the traditional continuous flooding method was observed at ?30 kPa, which was reduced by 24–82% for the other soil moisture levels. The performance of Pathumthani 1 was better under the DDS method at all soil moisture levels. The threshold level of AWD could be ?30 kPa for soil and weather conditions comparable to the present study for its high water productivity compared with yield reduction.

Alternate wetting and drying; Continuous flooding; Dry direct seeding; Water productivity; Wet direct seeding

Freshwater resources around the world are consistently declining, leading toward competition for this precious natural resource. Agricultural water availability is steadily decreasing for various reasons, including competition among different economic sectors, reduced investment in irrigation infrastructure, water quality deterioration due to pollution, and alarming population growth (Rijsberman, 2006; Datta et al., 2017). In most of the Asian countries, per capita availability of water declined by 40–60% between 1955 and 1990 and is projected to decline further by 15–54% over the next 35 years (Gleick, 1993). Agricultural production needs to be doubled in the twenty-first century to feed the growing world population in the context of decreasing water availability for agricultural purposes (Foley et al., 2011). It is, therefore, necessary to find alternative methods with fewer water inputs for agricultural purposes in order to maintain productivity and sustainability. Rice (Oryza sativa L.) is the main staple food crop for almost one-third of the global population who are mostly poor, and thus it is critically important to global food security (Ullah et al., 2018). Rice is not an exclusive hydrophyte, but its cultivation under inundated conditions has been in practice for a long time. On average, rice production requires double the amount of water for each unit of production than for that of any other cereal crop (Maclean et al., 2002). A total of 93 million ha of irrigated lowland area provides 75% of the world’s rice production, and increasing water scarcity can threaten the sustainability of its production. A considerable amount of water is lost from rice fields during land preparation and the crop-growth period through unproductive evaporation, seepage, and percolation flows (Bouman & Tuong, 2001). Therefore, wastage of freshwater in the rice field needs to be minimized because more irrigated land is devoted to rice production than to any other crop in the world (IRRI, 2003). Rice is a primary source of caloric intake for most Asian people. Most of the Asian countries face severe challenges of rapid population growth, widespread poverty, and vulnerability of its major rice-producing areas to climate change. By 2025, 15–20 million ha of irrigated rice land is projected to suffer from some degree of water scarcity (Tuong & Bouman, 2003). Therefore, it is of the utmost importance to identify alternative methods by which more food can be produced with less water, given the projected increase in freshwater scarcity for irrigated agriculture and the rising demand of food in the coming future.

The water-use efficiency of rice is very low in the Asian region, especially for small farmers, who could contribute 75% of rice production in the coming decade. The yield gap in this region is very high, and there is a general belief that this gap could be narrowed through the efficient use of resources and increased water-use efficiency of rice. For this reason, a number of rice production management strategies have been developed, some of which are closely related. Among these techniques, the most common are alternate wetting and drying (AWD) (Belder et al., 2004), integrated crop management, aerobic rice culture (Bouman & Tuong, 2001), use of controlled-release fertilizers (Shoji & Kanno, 1994), and the system of rice intensification (SRI) (Stoop et al., 2002). DS is also an important strategy for efficient water management. This technique is very useful in reducing water loss during land preparation. Because rice is a high water-demanding crop, a slight decrease in water input for its cultivation would save huge amounts of freshwater, which could be used for other economic sectors, or would allow further areas to be brought under cultivation. A major shift has been observed in Asia toward adopting the DS method of cultivation due to increasing water scarcity and high labor wages (Datta et al., 2017; Ullah et al., 2017). Farmers in areas with sufficient irrigation water and labor availability practice the traditional transplanting cultivation method, in which fields remain flooded for most of the growing period, but farmers in areas with shortages of water and labor generally prefer water-saving cultivation techniques. The dire predictions for 2025 indicate a serious water shortage problem for irrigated rice cultivation in most of the rice-growing areas, including Thailand. On the other hand, most of the popularly grown rice varieties are cultivated under lowland conditions, and evaluation of the performance of such varieties under water-saving cultivation techniques is critically important. Therefore, the present study was designed to evaluate the performance of a popularly grown rice variety, Pathumthani 1, under different cultivation methods and thresholds of AWD water regime.

A water-saving cultivation method (DDS or WDS) could be safely recommended for the tested rice variety under soil and weather conditions comparable to the present study. Pathumthani 1 performed better under DDS in all soil moisture regimes and could be adopted as a water-saving cultivation technique. Application of different soil moisture regimes helped save significant amounts of water compared with traditional flooding conditions, albeit with some yield penalty. The threshold AWD level of –30 kPa could be recommended, resulting in some degree of yield loss but with a high water-saving potential for soil and weather conditions comparable to the present study. Evaluation of the current study under field conditions is recommended to validate the experimental findings.

The authors thank the Higher Education Commission, Pakistan, and the Asian Institute of Technology, Thailand, for providing financial assistance with a scholarship to the first author for graduate studies at the Asian Institute of Technology, Thailand.

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