RICE RATOONING - IRRI books - International Rice Research Institute

AGRONOMIC PRINCIPLES AND PRACTICES OF RATOONING 169Table 6. Effect of nitrogen level on grain yield of IR28 ratoon a (4).N level(kg/ha)020406080Grain yield(t/ha)1.0 b1.0 b1.1 b1.5 a1.5 aa Av of 4 replications. Means followed by a common letter are not significantlydifferent at the 5% level.Table 7. Ratoon grain yield and yield components of Aiyou 2 rice as affected bydifferent levels of nitrogen applied 2 wk before main crop harvest in SichuanProvince, China, 1981 a (45).Nitrogen levelTiller(kg/ha) (no./m 2 )Panicle(no./m 2 )Grain yield(t/ha)69340435 a360 b230 c306 a277 a192 b2.9 a2.7 a1.9 ba Av of 3 replications. In a column, means followed by the same letter are not significantlydifferent at the 5% level.Table 8. Grain yield and other plant characters of ratooned rices as affected by method of nitrogenapplication to the main crop a (44).ApplicationSplitPlacementmethodPlant height b Tiller b Panicle Grain yield(cm) (no./m 2 ) (no./m 2 ) (t/ha)IR36 IR42 IR36 IR42 IR36 IR42 IR36 IR4260 b 67 a 226 a 345 b 190 a 277 a 0.9 b 1.4 b64 a 66 a 254 a 403 a 210 a 325 a 1.2 a 1.6 aa Av of 4 replications and 4 seedling ages. In a column, means followed by a common letter arenot significantly different at the 5% level. b At harvest.IRRI, grain yield significantly increased as N rate increased; N level was optimal at60 kg/ha (4) (Table 6). In China, as N increased from 0 to 69 kg/ha, ratoon tillernumbers of Aiyou 2 rice increased significantly (45) (Table 7). However, N level forpanicle number and grain yield was optimal at 34 kg/ha. In Colombia, CICA-4 riceratoon yielded 3.8 t/ha with the application of 25-50 kg N/ha (42). In Texas, only 50or 70 kg additional N/ha (approximately 3/4 of the recommended N for the maincrop) [14,21] was required for the ratoon crop (2). Although excessive N applicationincreased sprouting rate (25), it weakened the plant and resulted in a markeddecrease in ratoon crop viability (23). High N application also delayed ratoon cropmaturity (6).Method of N application in the main crop also affected the ratoon crop (41,44). Deep placement of N in the main crop significantly increased height of IR36ratoons, tiller number of IR42 ratoons, and yield of ratoons of both cultivars (44)(Table 8). Deep placement produced 15% higher ratoon yield and higher panicledensity than split application. Split N application in the main crop resulted indelayed maturity and lower leaf area index of the ratoon crop. Samson (41) also