Planting date affects grain and milling yields of water-seeded clearfield rice

Planting date affects rice grain and milling yields. However, no such research has been conducted on the imidazolinone-tolerant Clearfield (BASF Corporation, Ludwigshafen, Germany) rice, which has been rapidly adopted in the southern USA since 2003. To investigate the planting date effects on rice grain and milling yields, a field test involving both Clearfield and conventional rice cultivars was water-seeded at 2-wk intervals from late February to early July from 20032005 in Crowley, LA. Our results indicated that both Clearfield and conventional rice planted between I April and mid April produced the highest grain yield. Grain yield gradually declined at the two subsequent May planting dates, with dramatic reductions occurring thereafter. The pooled grain yields across years and cultivars were 7.94 Mg ha(-1) for two April plantings, followed by 6.76 and 6.28 Mg ha(-1) for early and mid May plantings, respectively. However, the two delayed plantings in early June and late June or early July produced the lowest grain yields of 4.51 and 3.64 Mg ha(-1) respectively. The highest head rice yield of 652 g kg(-1) was observed at mid-April planting dates, followed by 638 g kg(-1) at mid-May planting dates. However, rice seeded immediately after those two dates had the lowest head rice yields of 606 and 597 g kg(-1) respectively, which might be related to the low seedling stand and/or hot and dry weather during late August and early September when the rice headed. Therefore, water seeding of both Clearfield and conventional rice should occur from 1 April to mid-April in southwest Louisiana to maximize both grain and milling yields.