RICE RATOONING - IRRI books - International Rice Research Institute

74 RICE RATOONINGrice observed at the University as well as on private farms of two hill zone districts(Kodagu and Chikkamagalur) impelled rice researchers to take up varietal,agronomic, and plant protection studies in collaboration with the International RiceResearch Institute (IRRI), Philippines.Ratoon yields ranging from 77 to 140% of the main crop yield in 66-72% of themain crop duration were realized in the hill region with Intan rice (Table 2). InBangalore, Mangala planted in August and harvested at the end of Novemberproduced the highest ratoon yield (7) (Table 2). Short-duration varieties such asCH 45, CT 1351, S 705, Mangala, and Intan mutant also showed moderate ratoonyields in Bangalore (21).Two experiments conducted at Kodemadkal Government Farm, Mudigere,Chikkamagalur District, to screen and evaluate 69 genotypes showed ratoon cropyield ranging from 76 to 350% of main crop yields (19). On an average, the ratooncrop had 24% shorter growth duration.Data gathered from several private farms in the Chikkamagalur Districtrevealed wide fluctuations in ratoon crop yields (0.74.6 t/ha) compared with maincrop yields (1.1-7.8 t/ha). Probable causes were time of main crop harvest, stubbleheight, and fertilizer applied to the ratoon crop. The early-cut ratoon plots(November to mid-December) exhibited maximum yield fluctuations in the ratooncrops, flowering under low winter temperatures which prevented proper panicleexsertion and caused high spikelet sterility.Failure of ratoon crops also has been observed in plots with soil affected byiron and aluminum toxicity and phosphorus deficiency, where even the main cropstand was below normal (personal observation of T. G. Reddy and A. Manjunath).The ratoon cropping practices recommended now are• use only Intan variety,• select only plots with good main crop stand,• dry the field for 8-10 d,• cut main crop to stubble height of 7.5-10 cm,• resume light irrigation when ratoon growth becomes visible, and• weed and topdress ratoon crop with 50 kg N/ha 1 mo after cutting of maincrop (3).These general recommendations need to be refined to fit varying main cropcutting times, topographic situations, and soil conditions; studies with genotypes ofvarying growth duration for different planting dates are needed. In ChikkamagalurDistrict, with the introduction of ratoon cropping with Intan rice, farmers havethemselves selected one more local variety — Aluvbatta, which occupies a sizablearea between Mudigere and Chikkamagalur — for ratoon cropping. This varietyneeds to be evaluated for its potential as a main crop for direct use and its worth in abreeding program. An introduction from the Dominican Republic, Mingolo, hasbeen identified as equivalent to Intan in all respects (plant height, virus and blastresistance, ratooning ability, and grain quality) except growth duration. This is beingevaluated for late main crop harvests and the variety is fast being adopted byfarmers.