Drain and harvest timing affects on rice grain drying and whole-milled grain
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The economic value of a rice (Oryza sativa) crop depends mainly on percent whole-milled grain (milling quality) production. Whole-milled grain depends on preharvest drying conditions, harvest grain moisture (GM), postharvest management, and mill management. Research was conducted at the Texas A&M University Agricultural Research and Extension Center near Beaumont, TX from 1989 to 1992 to evaluate the effect of drain and harvest timing on grain drying patterns of rice and whole-milled grain. The study was laid out in a split plot design with drain date as main plot and harvest date as subplots. 'Lemont' rice was drill-planted in (12-18.2) m 36.5 m plots on 0.2 m centers at 112 kg ha-1 and received uniform management from planting to 7 days after heading (DAH). Main plots were drained at 4-day intervals from 7 to 27 DAH (draining 24-27 DAH traditional). Subplots were harvested at 2-day intervals from 350 to 150 g kg-1 GM. Drain date did not significantly affect yield or whole-milled grain. Field drying patterns for rice were influenced by year and harvest sequence. There was no apparent relationship between key weather conditions and drying pattern. Drain time influenced drying patterns mainly for drains at 7 and 11 DAH. Drying patterns for drains of 15 and 19 DAH were similar to the more traditional 23 and 27 DAH (7-12 days before harvest) drains. GM converged for all drain dates at lower GM levels. GM declined about 22 g kg-1 per day above 230 g kg-1, but declined only about 0.6 g kg-1 per day from 23 to 15 g kg-1. Draining at 7 DAH reduced whole-milled grain at least 5%. Whole-milled grain fluctuated among years but the impact of key climatic conditions was complex. Late rainfall, after 123 days after planting (DAP), appeared to influence the maximum whole-milled grain. The influence of rainfall prior to 123 DAP was not apparent. Averaged over years, whole-milled grain increased until 133 DAP. Under the conditions of this study, whole-milled grain was similar between 170 and 200 g kg-1 GM. Rice should be harvested from 127 to 130 DAP (210-170 g kg-1 GM) to optimize whole-milled grain. These factors may have a more dramatic impact on small plot studies where treatments resulted in large GM differences than in field conditions. 2002 Elsevier Science B.V. All rights reserved.