RICE RATOONING - IRRI books - International Rice Research Institute

168 RICE RATOONINGTable 5. Effect of main-crop cutting height on percentage of missing hills andgrain yield of IR28 ratoon (4).Cutting height(cm)51520Missing hills(%)37 b12 a5 aGrain yield(t/ha)0.9 b1.3 a1.5 aa AV of 4 replications. In a column, means followed by a common letter are notsignificantly different et the 5% level.However, irrespective of stand establishment method, with increased tillernumber per unit area, the crop is more prone to lodge. Greater lodging resistanceshould be incorporated into cultivars to minimize yield and quality losses.Cutting heightAmong the ratoon plant characters greatly affected by cutting height are grain yield,tillering, and growth duration. However, the response of grain yield to cutting heighthas been inconsistent.In Colombia, plants cut at 15 cm gave higher yields than plants cut at groundlevel (42). At IRRI, cutting at 15 cm also encouraged tillering, significantly reducingmissing hills and increasing grain yield over cutting at 5 cm (4) (Table 5). In India,cutting close to the ground produced the lowest yield; the best cutting height was35 cm (43). In Ethiopia, ratoon yield was significantly higher when the main cropwas cut at ground level, although tillering percentage increased as cutting heightincreased from ground level to 12 cm high (38). In the Philippines, ground-levelcutting was suggested to prevent growth of unproductive tillers (35). In Japan,ratoon stand varied with cutting height but grain yield did not (30).The effect of cutting height on ratooning and growth duration was consistent.Higher cutting height always resulted in improved tillering (4, 30, 38) and shortergrowth duration (4, 14, 21, 41). The ideal cutting height appears to be about 15 cmabove ground level.Fertilizer managementFertilizer is another input that greatly influences growth and yield of rice ratoons.But requirements vary widely. Some studies indicate that growth of the ratoon isdependent on composition and rate of fertilizer used (12, 17); others, that fertilizermixtures are needed not only on the main crop, but also on the ratoon crop (46). Butin other studies, only N fertilizer had a significant effect on ratoon performance. InTaiwan, P and K did not affect ratoon grain yield (25). In Texas, P and K applicationon the ratoon crop was not necessary if the main crop received adequate amounts ofthose elements (15). Sufficient amounts of P and K applied to the main crop werestill available to the ratoon crop (13).Nitrogen has been observed to improve tillering and increase grain yield of theratoon crop. However, responses of ratoon to N rate were not consistent. In someinstances, N level did not affect tiller and panicle number, 100-grain weight, grainstrawratio, and missing hills (3). In other cases, tiller number gradually increasedwith increasing N level, although ratoon weight was not significantly affected (5). At