Yield and Yield Components of Southern Long- and Medium-Grain Rice as Affected by Planting Dates and Seeding Rates.

Delayed planting can significantly reduce rice grain yield. Previous research using traditional rice varieties suggested that the yield reduction of late-planted rice was attributed to fewer panicles per unit area and/or smaller panicle size. By using six recently released southern long- and medium-grain rice cultivars, this study was conducted during 2007-08 at Louisiana State University AgCenter’s Rice Research Station near Crowley, LA to determine yield and its components at three planting dates (earliest and latest recommended dates and two weeks after the recommended date) and two seeding rates (1X and 1.5X recommended rate). It was also aimed to elucidate whether some or all yield components are affected by different seeding dates and whether yield loss of late-planted rice can be compensated for by higher seeding rates.

Our results indicated that yield reductions of both long- and medium-grain rice after the recommended planting date primarily resulted from a lower number of panicles per unit area, lighter grain weight, and to the less extend, fewer filled grains per panicle. The average number of panicles per square meter was 311, 349, and 356 for the mid-May, mid-March, and late-April planting dates, respectively. The mean grain weight from the mid-May planting was 23.5 mg, while the mid-April and mid-March planting had mean grain weight of 25.0 mg and 25.5 mg, respectively. The highest average number of spikelet per panicle was observed at mid-May planting dates followed by mid-March and mid-April dates; however, grain fertility decreased as planting date was delayed. Average seed set for the mid-March planting dates was the highest at 78.5%, while that for mid-May plantings was only 71.4%. The 1.5X recommended seeding rate failed to produce higher grain yields than the normal seeding rate for the mid-May planting dates. The 50% of additional seed only added 6.8% more panicles (350 m^-2 vs 327 m^-2).