RICE RATOONING - IRRI books - International Rice Research Institute

190 RICE RATOONINGRESULTSMain crop N rate and timing effect on main crop yieldLabelle main crop yields without N fertilizer are about 2.0 t/ha on Beaumont clay or3.5 t/ha on Edna very fine sandy loam at Ganado. Without N, main crop yields ofLemont are usually 3.0 t/ha on Beaumont and 4.0 t/ha on Ganado soil. The time ofapplying main crop postflood N (N applied after flooding and during thereproductive stage) influenced main crop yield. Applying N at PD stage of Labelleand Lemont always produced highest yields, and represents a common fertilizerpractice for commercial rice production in the southern U.S. Applying N at initialheading or at 2 wk after initial heading rather than at PD tended to reduce main cropyields by 0.1 to 1.0t/ha, especially at lower N rates, probably because the main cropbecame N deficient during PD (Tables 1, 2, and 3).As the total N applied by the PD stage increased from 79 to 167 kg N/ha, themain crop yield of Labelle increased from 4.9 to 6.6 t/ha (Table 1). Yields of maincrop Lemont at Beaumont increased from 7.5 to 8.6 t/ha as N applied up to the PDstage increased from 117 to 224 kg N/ha (Table 2). However, Lemont yield increasesat Ganado (Table 3) were only from 8.2 to 8.6 t/ha for the same N rates.Main crop N rate and timing effect on ratoon crop yieldEven though the main crop yields increased with total N applied at the main crop PDgrowth stage, ratoon crop yields of either cultivar were not related to main crop Nrate or main crop yield. As total N increased from 79 to 167 kg N/ha for Labelle,ratoon crop yield stayed between 1.6 and 1.8 t/ha (Table 1). Lemont ratoon cropyield at Beaumont varied from 1.9 to 1.8 t/ha as N rate increased from 117 to 224 kgN/ha. At the Ganado site (Table 3) the change in Lemont ratoon crop yield as Nincreased was greater (1.9 to 2.4 t/ha) than at the Beaumont site, but ratoon cropyield did not always increase with main crop N rate.Table 1. Effect of N management on ratoon and main crop yields of Labelle grown at Beaumont,Texas, in 1984 and 1985 (all N applied by the PD stage).N fertilizer rate andTreatment application time a Total N Yield (t/ha)(no.)PP PF PD Hd Hd2(kg/ha)Main crop Ratoon crop b Total113 kg N/ha12345167 kg N/ha123453434343434505050505045454545456757676767034170005025000017340002550000003400005079113113113113117167167167167LSD (.05)4.95.75.64.75.05.76.66.55.95.9= 0.31.81.71.71.81.81.71.61.71.82.0n.s.6.77.47.36.56.67.48.28.27.77.90.3a PP = preplant, PF = permanent flood, PD = panicle differentiation, Hd = heading, Hd2 = 2 wkafter initial heading. b Ratoon crop yield when no N was applied at main crop harvest.