Crop Management & Environ-mental Effects on Rice
Milling Quality & Yield - 2008



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Project Leader and Principal  Investigators

Randall "Cass" Mutters, farm advisor, UC Cooperative Extension, Butte County

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

Richard Plant, professor, Dept. of Plant Sciences, UC Davis


This is the sixth year of a project examining how crop management decisions and field moisture conditions affect rice milling quality and yield. This work has significant implications for how rice is harvested and could lead to a reduction in drying costs.

Tests at the Rice Experiment Station (RES) and at yield trials near Colusa and Natomas have demonstrated for three straight years that M-206 rice will maintain high head-rice quality over a wide range of harvest moisture (as low as 15 percent) when it is drained early. Variety M-205 demonstrated better stability in head rice quality than M-202 but not quite as good as M-206.

Harvesting at lower moisture contents would allow the rice industry to save money by reducing drying costs. More detail about this research follows.

Field and laboratory experiments

A field experiment at RES in 2008 compared M-202, M-205 and M-206 rice planted in three basins at a seeding rate of 150 pounds/acre. 
The rice was grown under identical cultural practices. A meteorological station measured air temperature, relative humidity, leaf wetness and soil moisture to quantify differences between basins.

Target drain dates were seven, 14, and 21 days after 50 percent heading. However, heading dates among test varieties varied by several days. As a result, actual drain dates for the seven-day treatment were nine, five and 13 days after heading for M-202, M-205 and M-206, respectively.  Similar adjustments were made to the 14- and 21-day drain target dates. Rice was harvested and samples collected Oct. 13, 16, 20, and 23 at RES. At the other, off-station plots, samples were harvested at several dates to obtain a range of harvest moistures.

In controlled laboratory experiments to determine the effect of moisture exposure on fissuring of
M-202, M-205, and M-206, rice kernels were soaked for periods ranging from zero to 24 hours and then dried back to 14 percent moisture content before milling. This research helped verify that M-206 is less susceptible to fissuring than either M-205 or, especially, M-202.

Drain time and dew effects

A better understanding of soil moisture content and loss rate is important to establish appropriate drain times because of the potential for moisture to influence rice kernel fissuring and thus head
rice yield.

After draining, basins at the RES experiment dried at comparable rates across treatments. This study showed that a soil moisture content of 20 percent when rice first reaches acceptable harvest moisture (about 21 percent) might prove to be a good benchmark to ensure good harvest yields. There was no observed decline in yield or milling yield in plots where the soil moisture remained above 20 percent during grain ripening.

Kernel fissuring can be greatly influenced by dew on panicles. For instance, results from 2007 indicated that M-206 fissured when exposed to more than eight hours of dew. In 2008, leaf wetness sensors were used to refine dew measurements.

Indications are that drain time and soil water content may influence the number of dew events. However, in 2008 there were not enough high humidity days to significantly reduce head rice yield, even in the sensitive M-202 variety.

Results from 2008 partially confirm results from previous years’ research – that head rice yields of M-205 and M-206 remain stable across a range of harvest moisture contents. In contrast to previous years, however, the head rice yield at different moisture contents in 2008 was not influenced by an early drain time or weather. This was because of the few dew events occurring during the harvest period. In 2008 only four nights of dew were observed at the research site (compared to 12 in 2007).

Samples taken adjacent to the statewide variety trials near Colusa and Natomas showed that both M-205 and M-206 produced higher head rice yield compared to M-202 when harvested at low moisture content. When moisture content was above 22 percent, there were no significant differences in head rice yield.  The superiority of M-205 and M-206 was clearly evident with moisture content levels below 18 percent.

 This research shows that the newer varieties may be drained earlier than is current common practice. More information is needed, especially on lighter textured soils, but early draining may allow growers to reduce water requirements for rice crop production in these varieties.


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