Drain Time and Crop
Management Effects on Milling
Quality and Yield-04


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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 project is studying how dew formation and drying winds influence head rice yield and grower returns.

A controlled experiment at the Rice Experiment Station with M-202 medium grain had shown previously that good head rice yield could be maintained even at low harvest moisture if field rice is not subjected to rehydration from dew before harvest.  In a new round of related experiments with M-202, one test plot was drained September 7 and two others on September 15.  All basins were harvested on September 22, 27, 30 and October 4, 11 and 15. Each plot was hand harvested in six locations and threshed with a small-plot thresher.  Rice moisture for each harvest location was determined with a single grain moisture meter.

 Paddy moisture remained consistently high, above 23 percent during the first 12 days of the test.  Head rice also remained high during this period.  Between October 8 through the 13th, however, a north wind caused average moisture to drop to 11.8 percent.  Head rice yield declined 8 percent in this period.  After the wind stopped, night dew returned and after two days of rewetting, head rice yield plummeted to 26 percent.  Rice value (loan value minus drying costs) dropped significantly during this period from $5.60/cwt on October 4 to $3.90/cwt on October 16.

Researchers also recorded an increase in average yield from 7,400 pounds/ acre on September 22 to 9,800 pounds/acre on October 4.  This was somewhat surprising since moisture changed very little during that period.  They conclude that moisture is not a good indicator of yield.  Yield potential is more closely related to the number of high moisture kernels in a harvested sample.  The number of green kernels may be a better indicator of yield than average rice moisture. 

Rice yield in this experiment increased by more than 30 percent after it reached moistures that are typically considered suitable for harvest.  Combining yield data with rice value will produce a more accurate picture of grower return in dollars per acre. 

In the experimental plot, returns increased to $557/acre during a period of north wind in early October.  After the wind stopped, the loss in head rice reduced returns to $389/acre within days (see figure).  High head rice yield is still possible if rice doesn’t dry below 20 to 24 percent moisture before dew returns.

The practical implications of these observations are that harvest should proceed at maximum possible rates during dry meteorological conditions.  Growers receive the greatest value for their crop under these conditions.  After the return of dew-forming conditions, head rice yield, rice value and grower returns decrease dramatically.

Future research should be geared toward confirming these patterns of increased yield after rice drops to harvestable moisture.  This is especially needed for varie-ties with a large range of flowering and heading dates.  The industry needs an indicator of agronomic maturity because rice moisture is not a good predictor of yield.

Researchers also completed analysis of a 2003 study examining the relationship between grain fissuring and drain time or harvest date.  No meaningful differences in apparent amylose, protein, RVA paste viscosity, or taste panel evaluation or sensory quality and drain time or harvest date were observed.


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