Irrigated transplanted rice is a prolific user of water. According to one estimate it takes up to 3,000 liters of water to produce 1 kg of rice. However, due to looming water crisis we have to look for ways such that we increase water productivity in rice. We envisage that even a small savings of water due to a change in the current practices will translate into a significant bearing on reducing the total consumption of fresh water for rice farming.
Therefore, we undertook this study to identify rice varieties, both inbreds and hybrids, suitable for alternate wetting-and-drying (AWD) irrigation during the vegetative phase, saving around 17% of water, without any significant reduction in yield. In fact, we have observed a great deal of genetic variation for tolerance to water stress during the vegetative phase and have identified promising inbred and hybrid genotypes for further study to elucidate the underlying mechanisms. Our data suggest that 18 of the 31 inbreds bred for irrigated ecology did not experience any significant decline in yield due to AWD. Similarly, there was no significant yield decline in 3 of 7 hybrids tested. We have identified three hybrids and six inbreds which are water-efficient and produced 5.5 t/ha or more under AWD conditions with no significant yield loss as compared to conventional irrigated conditions.
We have identified elite hybrids and inbred lines suitable for growing under alternate-wetting and drying conditions thus saving around 17% irrigation water, without sacrificing yield.
Water saving technology, conventional irrigation, germplasm, genetic variability.
Irrigated transplanted rice on puddled soil is the traditional system practiced over several centuries in Asia. Irrigated rice is a prolific user of water and it uses two to three times more water than other important cereals such as wheat and maize. However, over the past decade there had been declining quality and availability as well as increasing competition and cost of fresh water that threaten the sustainability of the irrigated rice system in Asia. Tuong and Bowman (2003) estimate that, by 2025, about 2 million ha of Asia’s irrigated dry-season rice and 13 million ha of its irrigated wet-season rice will experience “physical water scarcity,” and most of the 22 million ha of irrigated dry-season rice in South and Southeast Asia will suffer “economic water scarcity.” To tackle this problem of severe water shortage for rice production, we urgently need new methods of irrigation to save water and related crop management technologies to sustain yield (Bouman and Tuong 2001, Tuong and Bouman 2003).
During the 1990s, IRRI and national researchers successfully tested several water-saving technologies such as saturated soil culture, saturated soil and soil drying, and alternate wetting and drying (AWD) in farmers’ fields. These methods have been reported to increase water productivity by reducing water input by up to 35% compared with continuous flooding, but grain yield decreased (Borell et al 1997, Lu et al 2000, Bouman and Tuong 2001, Tabbal et al 2002). To maintain yield, AWD appears to be promising because of its high water productivity with the lowest penalty to grain yield. In trials conducted in China and the Philippines, reported savings in water for AWD range from 13% to 30%, with no significant reduction in yield (Cabangon et al 2001, Belder et al 2002).
Two major factors, the use of inappropriate rice varieties and inadequate weed management, appear to be responsible for yield loss under AWD (Tabbal et al 1992, Shi et al 2002). In the present study we have evaluated several elite inbred lines, varieties, and hybrids under AWD during the vegetative phase, with a view to identify promising high yielding genotypes without any significant loss of yield due to AWD in comparison with traditional puddle system. In many areas such as Punjab (India), a traditional wheat belt, where rice-wheat is intensively grown, the water table receded on average 0.2 m per year during 1979-1991 (Singla 1992). The area under the critical water table below 10 m in central Punjab increased from 3% in 1973 to 25% in 1990 and 53% in 2000.
To tackle this problem of severe water shortage for rice production, we urgently need new methods of irrigation and appropriate varieties to save water and related crop management technologies to sustain yield (Bouman and Tuong 2001, Tuong and Bouman 2003). In this study we are testing one of the promising water saving technology namely alternate wetting and drying coupled with the selection of appropriate rice hybrids and inbred varieties.
Forty-four genotypes (7 hybrids and 37 inbreds) were evaluated during 2003 dry season at IRRI (Table1) under conventional puddled irrigation (CI) and alternate wetting and drying conditions (AWD) . A randomized complete block design with four replications and 5 m long plots of 10 rows was used in each of the experiments. A uniform spacing of 20 cm between rows and between hills within rows was maintained. The grain yield in t/ha was recorded from each of the plots at maturity from 6 m2 harvested area. In all 6 AWD cycles were applied. The first AWD cycle was initiated 3 weeks after transplanting. In each of the AWD cycle 5 cm water depth was attained and the field was re-irrigated after the water level had receded to 25 cm below ground.
In comparison to the conventional irrigation conditions, a saving of 17% of water was achieved in the alternate wetting-drying method. Yield losses due to AWD varied from 3 to 23% for the hybrids while for inbred it varied from a gain of 6% to a loss of 26%. Apparently the pattern of response of both hybrids and inbreds is quite similar under CI and AWD. There was no correlation between yield obtained from AWD and CI methods suggesting a significant genotype x environment interaction.
Interestingly, 18 of the 31 inbred lines bred for irrigated ecology did not experience any significant decline in yield due to AWD. In fact, there was some evidence of yield gain due to AWD for 4 entries. Also, there was no significant yield decline in 3 of 7 hybrids tested, due to AWD method. On the other hand, for varieties and elite lines suitable for rainfed ecology, 3 of the 6 inbreds suffered a significant yield decline due to AWD. Three hybrids and six inbreds were found to be water-efficient and they produced 5.5 t/ha or more under AWD conditions with no significant yield loss as compared to conventional irrigated conditions (Figure 1).
Table 1. A list of the material used in the present study.
IR77266H, IR77843H, IR78386H, IR80224H, IR80227H, IR80228H, MAGAT
IR69715-72-1-3, IR71604-4-1-4-7-10-2-1-3, IR71700-247-1-1-2,
CT6510-24-1-2, IR68098-B-78-2-2-B-1, IR20, PSBRc70, PSB Rc9, PSBRc68
Figure 1. Yield kg/ha of nine promising inbreds and hybrids under irrigated and AWD conditions
There is a great deal of genetic variability for tolerance to relatively mild water stress conditions during the vegetative phase in both hybrids and inbreds. Three promising hybrids and six inbred varieties have been identified for limited water stress conditions at least during vegetative phase. We are conducting further experiments during 2004 dry season and for the promising candidate materials it would be critical to develop appropriate crop management practices to ensure early seedling vigor, high tillering, and high yield for rice under AWD.
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