RICE RATOONING - IRRI books - International Rice Research Institute

164 RICE RATOONINGEFFECT OF ENVIRONMENTAmong the environmental factors affecting plant growth, temperature and lighthave been found to greatly influence ratooning performance, particularly tillerproduction.TemperatureAmong other plant traits, Ichii (26) studied differences in ratoon height andpercentage of ratoon tillers/cut plant exposed to high (30 °C) or low (20 °C)temperatures (Fig. 1). He noted that the higher the temperature, the greater theratoon plant height and percentage of tillers at early stages of development (5, 10,and 20 d after cutting). Maximum tillering was before 10 d at 30 °C and before 20 dat 20 °C.However, temperature had a different effect on plant characters in latergrowth stages. Plants exposed to low temperature (20/20 °C) at booting formed 3times more basal ratoon tillers than those exposed to high (35/27 °C) temperatureand 2 times more than those exposed to normal (29/21 °C) temperature (41)(Table 1). Total and productive tillers were significantly higher under low thanunder normal temperature. However, grain yield at 20/20 °C was significantly lowerthan yields at high and normal temperatures because of high spikelet sterility.Temperature also affected ratoon growth duration. Crop maturity lengthened from56 d at high temperature to 96 d at low temperature.Light intensityShading the main crop affected ratoon tillers, height, weight, and grain yield (28, 39).For example, ratoon height and percentage of tillers of plants grown under differentlight intensities (full sunlight, 50% shading, and 75% shading) for 2 wk before cuttingsignificantly decreased with increased shading (28) (Fig. 2). Maximum ratoon heightdiffered with light intensity, tillering did not. Maximum height was attained in 30 dat full sunlight, 25 d at 50% shading, and 20 d at 75% shading. Tillering stoppedaltogether at about 15 d, regardless of light intensity. Ratoon weight and percentageof tillers/cut plant were also lower in dark than in light environments (26). However,ratoons were taller in dark than in light environments.Shade duration also influenced ratoon growth (39). Shading from flowering ofthe main crop to 7 d after harvest (28 d) resulted in significantly lower ratoon yieldsTable 1. Plant characters of rice ratoon as influenced by temperature regime (4).Plant character aTemperatureregime (°C)Tillers (no./hill)Maturity Grain yieldDay Night Basal Total Productive (days) (g/hill)20 2029 2135 2733 a16 b11 b47 a27 b36 ab41 a26 b33 ab96 c 1.9 b61 b 5.7 a56 a5.8 aa Av of 4 replications and 2 (IR22 and IR36) rices. In a column, means followedby a common letter are not significantly different et the 5% level.