Performance of different rice varieties as influenced by water regimes under aerobic condition

The experiment assessed the growth and yield of four (4) varieties/lines as influenced by water regime during the dry season. The varieties/lines were PSBRc80 9control). IR 74371-54-1-1, IR 77080-B-34-3 and IR 71525- 19-1-1-1. Water regimes were once-a-week irrigation, twice-a-week irrigation and every-10-days irrigation. A 3 x 4 split-plot experiment in Randomized Complete Block Design with 4 replications was used. Results showed that the IR lines were genetically taller than PSBRc 80, the control variety. Except for plant height at flowering stage, there were no interaction effects observed. During the first 14-15 days after emergence (DAE), all the varieties showed comparable leaf area index (LAI). At 30-35 DAE, and 45-50 DAE, IR 770080-B-34-3 had greater (LAI) than IR 71525-19-1-1. At flowering stage, however, PSBRc 80 had significantly higher (LAI) than the IR lines. PSBRc 80 was the last to flower. Its biomass was significantly greater than the IT lines from the 30-35 DAE up to flowering. In general, irrigating twice a week and once a week significantly increased plant height up to maturity. LAI was only significantly influenced by frequency of irrigation during the flowering stage, while biomass at 45-50 DAE with twice a week and once a week irrigation, proving a better practice than every 10 days irrigation. The varieties flowered from 76 to 86 days after sowing with PSBRc 80 flowering significantly later than the IR lines. Days to flowering was significantly delayed by irrigating every 10 days compared to irrigating twice a week or once a week. PSBRc 80 produced significantly more productive tillers than IR 74371-54-1-1 and IR 715525-19-1-1 but number of spikelets per panicle, number of filled grains per panicle, and percent filled grains were significantly highest in IR 74371-54-1-1. All the varieties had similar length of panicle. Percent filled grains for all varieties/lines was low, ranging from 47.7 percent to 59.9 percent. This was attributed to the dry and hot condition prior to and up to flowering stage. The highest recorded temperature was 38.5oC, while the lowest relative humidity was 53%, a condition that might have caused desiccation of flowers during the period of pollination and spikelet sterility. Another factor was the heavy rain that occurred during the later part of the flowering stage. As a sequence, there was a low number of filled grains per panicle that eventually gave low yield. These two parameters were positively correlated. Yield of the varieties ranged from 0.86 tons to 1.82 tons per hectare. These are low compared to the yields obtained on aerobic rice in China, which ranged from 5 to 6 tons per hectare. Both IR 74371-54-1-1 and PSBRc 80 produced higher yield than IR 71525-19-1-1. Irrigating twice a week was more beneficial. It significantly increased the number of productive tillers, number of spikelets per panicle, number of filled grains per panicle, weight of 1000 grains, which resulted in significantly higher yield over plants irrigated once a week and every 10 days. Irrigating once a week also produced significantly higher yield than irrigating every 10 days. Harvest index of plants irrigated twice a week and once a week was significantly higher than those irrigated every 10 days. Yield was found to be significantly correlated with the number of productive tillers, number of filled grains per panicle and harvest index. On the other hand, harvest index and number of filled grains were also positively correlated. Low harvest indices of 0.12 to 0.22 were noted in all the varieties. IR 74371-54-1-1 and PSBRc 80, which had higher harvest indices of 0.22 and 0.16, respectively, produced significantly higher yields of 1.82 tons and 1.62 tons per hectare than the two other IR lines. Water productivity differed among varieties/lines and among water regimes. The trend of water productivity was IR 74371-54-1-1 PSBRc 80 IR 77080-B-34-1 IR 71525-19-1-1 and twice a week irrigation once a week irrigation once every 10 days irrigation. Water productivity ranged from 0.13 to 0.28 kg grain/m3 water.