RICE RATOONING - IRRI books - International Rice Research Institute

180 RICE RATOONINGestablished; the information now available is scanty. Cutting the growing stubblemore than once also appears to offer scope for manipulating ratoon duration andyield components (8).Fertilizer managementAlthough research results on the timing and dosage of fertilizer applied to the ratooncrop are inconsistent, plots fertilized with N and other nutrients have always yieldedmore (25, 26, 33). Soil fertility status, ratoon crop growth duration, topography ofratoon crop plots (mid- and lowlands in areas where P deficiency and Fe and A1toxicity are common) vary enormously. Experiments on these aspects are needed todetermine optimum doses of nutrients for each growing condition. P and Ca mayhave a definite bearing on ratoon crop yields in acid soils.Water managementWater management immediately before and after main crop harvest influencesratoon stand and tiller production. Most studies in the past conclude thatwithdrawal of water some days before harvest, leaving only moist soil, and irrigatingas ratoon growth progressed encouraged ratoon crop production. Since significantinteraction is reported between cutting height and water management in ratoongrowth, as well as flooding and weed control, this is an important aspect to study inareas with ratoon crop potential. Water management and nitrogen fertilization werereflected in increased yield and milling recovery with Labelle ratoon rice (12, 13).SEED PRODUCTIONSeed grain quality of the ratoon crop is one of the eight points Plucknett et a1 (21)listed as needing study. Main and ratoon crop yields as grain and as seed have beencompared. Except for seed viability, all other yield component characters (plantheight, panicle length, spikelet size, number of productive tillers, and grain setting)are less pronounced in the ratoon crop than in the main crop. Viability andproductivity of ratoon crop seeds have been found to be as good as those of the maincrop seeds (26, 28). Webb et a1 (31) reported ratoon crop grain of some varieties to berelatively less uniform. Protein content, although varying greatly, tended to beconsiderably higher in ratoon crop grain than in main crop grain. Gelatinizationtemperature and viscosity values were consistently lower for ratoon crop samples.Gay (7) reported that the quality of the ratoon crop grain harvested from Gulfrosevariety graded No. 1. Nadal and Carangal (18) observed that the grains produced bythe second ratoon were superior to those produced by the first ratoon. Nagaraja andMahadevappa (19) noted that the seed quality of main and ratoon crops varied withvariety and that the viability of ratoon crop seeds deteriorated faster than main cropseeds. However, the field performance of a variety remained unchanged, regardlessof whether the crop was raised from seed obtained from the main crop or from seedobtained from the ratoon crop (Table 1, 2).The ability of some genotypes, reported to have ratoon crop grain and seedquality as good as main crop seed quality (19), needs to be exploited by selecting suchgenotypes for a ratoon cropping system. Nutritional and other factors affecting