RICE RATOONING - IRRI books - International Rice Research Institute

RICE RATOONING IN RIO DE JANEIRO 57Table 2. Mean grain yield and growth duration of main crop and ratoon crop of three rice cultivarssown on different dates. 1978-79.Sowing CultivarGrowth duration (d)Main crop, Ratoon, firsta Yield (t/ha)emergence to harvest to Main Ratoon b Totalripening ratoon crop cropflowering18 Sep 197820 Oct 197821 Nov 197821 Dec 197823 Jan 197922 Feb 1979De AbrilIR841-63-5P899-55-6-4-6-1 BDe AbrilIR841-63-5P899-55-6-4-6-1BDe Abril*IR841-63-5P899-55-6-4-6-1BDe Abril*IR841-63-5*P899-55-6-46-1B*De Abril*IR841-63-5*P899-55-6-4-6-1B*De Abril*lR841-63-5*P899-55-6-4-6-1B*185154157161146145150149146145140141135142140142154154877376787474–8280–––––––––3.95.45.75.46.17.84.46.57.43.75.25.94.94.65.82.22.02.81.3 (34)3.4 (63)3.3 (58)0.8 (16)3.0 (49)3.2 (41)–0.4 (6)0.5 (6)–––––––––5.38.99.06.29.111.0–6.97.9–––––––––a * = no ratoon yield from crop sown on this date.b Figures in parentheses are percentages ofmain crop yield. Source: EEC, PESAGRO-RIO.the main crop, the improved varieties also had the best yields, except in the latesowings, where the yield of the traditional cultivar equaled those of the improvedcultivars IR841 and P899. The best performance of the ratoon crop occurred inSeptember and October. IR841 yields decreased with sowing dates from Septemberto November. Usually the harvest of cultivars with growth durations of 140-150 dwill occur in April, when the mean low temperature is about 18 °C. Because the riceratoon crop flowering stage will occur at low temperature, decreases in grain yielddue to spikelet sterility can be expected.In the second trial (Tables 3, 4, and 5), cultivar P899 and varieties Metica I andL-5738 had the best yields, up to 5 t/ha. Cutting at 10 cm above ground level loweredthe ratooning ability of all cultivars and varieties tested — maximum yield was16.8% that of the main crop in the variety MG209. The best ratoon yields were with acutting height at 30 cm above ground: the best responses were from PESAGRO-101,P899, De Abril, and Metica 1 — the yields doubled at 20 cm cutting height.P899 had the highest total yield (main crop + rice ratoon), more than 7 t/ha.Metica 1 and L-5738 also showed a high potential for rice ratooning with total yieldsmore than 6 t/ha at 30 cm cutting height. The lowest yields were with the traditionalcultivar De Abril (Table 3).The low total yield in the second trial was due to the low soil fertility, with only2% organic matter.In the main crop, growth duration ranged from 144 to 166 d. For all cultivarsand varieties, growth duration of the ratoon crop was about 60 d (Table 4).