RICE RATOONING - IRRI books - International Rice Research Institute

48 RICE RATOONINGplot size is 6 rows × 6.1 m with 17.8 cm row spacing. Plots are drill-seeded at112/kg ha and standard cultural practices are followed. From the 2 center rows, 4.88m are harvested by hand to determine yield. Following the main crop harvest, theborder rows are discarded, leaving a uniform stubble with a height about 70% that ofthe main crop. The stubble is topdressed with 67 kg N/ha. Ratoon plots are floodedto harvest. The same 2 rows used to measure main crop yield are used to measureratoon yield.The ratoon crop shows considerably more variability in grain yield than themain crop. Table 1 presents coefficients of variation for main crop yield, ratoon cropyield, and total yield in the Regional Uniform Rice Nurseries at Beaumont for 1977,1978, 1981, and 1982. In most years for most groups, the coefficients of variation forthe ratoon crop tended to be double or triple those for the main crop. The inherentlyhigher ratoon crop yield variability may be caused by main crop lodging; diseases;bird, rodent, and weather damage; soil nutrient deficiencies; and low temperature.Despite the high variability in ratoon data, the tests tend to identify superiorratooning lines. The correlation coefficient between 1977 and 1978 ratoon yields was0.508; between 1981 and 1982, it was 0.824. An example of the range of main andratoon crop yields in the very-early-maturing group of the 1978 Regional UniformRice Nurseries is presented in Table 2.Although ratooning ability is an important objective of the rice breedingprogram in Texas, the primary emphasis is on main crop yield. The main crop,which constitutes the major portion of the total yield, generally has better millingquality and is more stable and reliable than the ratoon crop. If a superior ratooningline is identified, it will be of value only if it is combined with satisfactory main cropyielding ability and with other important attributes required in a successful cultivar.When superior main and ratoon crop yielding abilities are combined in acultivar, extraordinarily high total yields are possible and the cost per unit ofproduction is reduced significantly. In 1985, a combined main and ratoon crop yieldof 13.6 t/ha was obtained with the semidwarf cultivar Lemont in research plots inLouisiana (3). In commercial production, a total main and ratoon crop yield of11.8 t/ha (12% moisture) was obtained on a 160-ha field of Lemont in Texas. TheTable 1. Coefficients of variation for main and ratoon crop yields in groups of theRegional Uniform Nurseries at Beaumont, Texas.Group I Group II Group Ill Group IV Group V Av1977Main crop yieldRatoon crop yield1978Main crop yieldRatoon crop yield1981Main crop yieldRatoon crop yield1982Main crop yieldRatoon crop yield5.411.37.734.311.28.312.317.44.216.65.321.39.011.1––7.8–14.3–7.719.3––4.227.39.937.9––––5.0–13.6–7.910.85.823.85.318.410.131.28.912.49.020.6