Crop Management and
Environmental Effects on Rice
Milling Quality and Yield - 2005



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Project Leader and Principal UC Investigators

Randall "Cass" Mutters, UCCE farm advisor, Butte county

James Thompson, extension specialist, Dept. of Biological and Agricultural Engineering, UC Davis




This is the third year of a project examining how rice moisture at harvest affects head rice yield and ultimately grower profitability.

A small plot at the Rice Experiment Station was divided into three sections and planted with M-202 at a seeding rate of 100, 150 or 200 pounds per acre. All sections were harvested on September 28 and October 4, 10, 14 and 19 and then analyzed for rice moisture, whole kernels and yield.

Researchers anticipated that the low seeding rate sections would have much greater tillering because of the low plant density, but the actual differences between sections were quite small. Weather conditions were atypical in 2005, so the cool weather in the early season may have reduced tillering below what it might have been in a more normal season.

Yields were constant across all harvests and at all seeding rates. This was quite different from 2004, when yields increased from 75 to almost 100 sacks per acre during a similar range of harvest times and moistures. The reason for the difference in yield pattern is unknown.

Head rice quality was better at the lower seeding rates during the last two harvest dates of the season. This may be related to the lower seeding rate having higher moisture than the high seeding rate. The differences in quality resulted in large differences in grower returns for all three seeding rates on the last two harvest dates.

The relationship between head rice yield and rice moisture at harvest followed the same pattern observed in the first two years of the study. Under high relative humidity at night prior to harvest, head rice yield drops precipitously when harvest moisture dips below 21 percent. Under dry conditions typically associated with north winds, rice will have a higher head rice yield because rehydration won’t occur during the night. Thus, good head rice yield can still be expected under dry conditions.

Growers need to be mindful, however, of variations in humidity associated with different microclimates and other variations associated with field draining or cultural practices. Nonetheless, it is still advisable to harvest rice at moistures greater than 21 percent whenever possible to prevent quality loss and diminished grower returns.


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