Crop Management & Environ-
mental Effects on Rice Milling Quality & Yield - 2010



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Project Leader and Principal  Investigators

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

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

Luis Espino, UC Cooperative Extension farm advisor, Colusa County




This continuing project is examining how crop management decisions and field moisture conditions affect rice milling quality and yield. Work also continued on the potential for water savings with accelerated field draining and an expanded survey of storage-related insects.

Guidelines developed for M-205, M-206

Rice varieties M-202, M205, and M-206 were again planted in a series of hydraulically isolated basins at the Rice Experiment Station. Each basin, equipped with individual water intake and drain outlets, allowed for discrete drain times without compromising soil water status. Irrigation water was supplied from a common feeder ditch.

Field preparation, fertility, and pest management followed standard RES practices. The experiment was planted May 25. Each variety was subjected to four different drain dates: 16, 20, 24, and 28 days after 50% heading. Drain times for M-202 were 24 and 28 days after 50% heading. Fifty percent heading occurred August 30 for M-202 and M-205, and August 20 for M-206—89, 90, and 86 days after planting, respectively. The experiment was harvested on October 13 and 19, and November 3, 5, and 12.

Environmental conditions were monitored from four weeks prior to the first harvest date to the final harvest date. Relative humidity and leaf wetness sensors were deployed at canopy level in all plots. Soil moisture content was taken at four locations in each basin and two depths to eight inches below the soil surface over a five-week period. Two meteorological stations also tracked temperature, relative humidity, and dew point. Single-kernel moisture measurements were taken mid-day beginning the third week of September to track when moisture content reached 30% and continued until the end of the harvest period.

Prior to the first drain date at the end of the season, water use in each basin was calculated on a daily basis. Three basins, one for each of the varieties studied, were equipped with water depth gauges.

Accumulated results over several years indicate it is not advisable to harvest M-205 or M-206 below 17% or above 24% grain moisture content due to the loss in head rice and total yield, respectively. This is likely because these varieties reach physiological maturity at lower moisture content than M-202.

Within each variety in the 2010 research, the rate of kernel drying below 25% moisture content was similar at all drain dates. The rate of moisture loss across varieties averaged 0.4% per day. The 16, 20, and 24 day-after-heading treatments reached harvestable moisture content three to five days sooner than the 28-day treatment. On the whole, yields increased as the drain date was delayed until 24 days after heading. There was no apparent advantage to postponing field draining beyond 24 days for M-205 or M-206. However, M-202 had higher yields at 28 days than 24 days.

Based on this year’s results—and those from previous tests—draining sooner than 20 days after 50% heading is not advised. By varying degrees, total rice yield and head rice yield of all varieties were unaffected by drain date. Total rice yield of M-205 and M-206 were particularly sensitive to harvest moisture content above 24%. Head rice yield was not affected by harvest moisture contents above 17%, indicating comparable sensitivity to environmental conditions during agronomic maturity of rice plants. However, head rice yield in test varieties may be affected by loss of flooded conditions if the soil transitions from anaerobic to aerobic conditions too early in the grain maturation process. Results from trials in 2009 suggest that the yield and quality performance of the test varieties were most sensitive to reduced soil moisture when grain moisture was above 27%.

End of season water use averaged across varieties was about 0.35 and 0.8 inches per day in 2010 and 2009, respectively. Shifting the drain date by a few days would result in nominal water savings at the individual field level.

Storage insect monitoring

Stored rice insect populations were surveyed in six locations of the Sacramento Valley in 2010. Two locations were in Richvale, one in Arbuckle and three in Glenn. In Richvale, one location is a dryer and stores dried rice from harvest until spring. The second location is a mill where dried rice is stored for short periods of time in silos before milling. The Arbuckle location is a mill that stores dried rice in silos and warehouses. The Glenn locations are farm bins where rice is stored from harvest until sold to a mill.

Pheromone and probe traps were used in this study. Grain, storage spaces, and farm bins were monitored. In grain stored in the Richvale flatbed warehouse, the most prevalent insect caught in pheromone and probe traps was the Angoumois grain moth (AGM), an internal grain feeder. This insect appeared at the beginning of spring and increased during the summer until grain was fumigated. In pheromone traps located around storage bins in the two mills, AGM and the lesser grain borer (LGB) were caught during spring and summer. The number of Indianmeal moths (IMM) caught was very low. In farm bins, mold-feeding beetles were prevalent. Their numbers decreased as ambient temperature dropped and grain dried. Pheromone traps inside farm bins did not catch any insects.

Late season management guidelines for M-205 and M-206

  • Field drainage—Fields can be drained 24 to 28 days after 50% heading without any loss in yield or milling quality in heavy basin soils.
  • Total rice yield—Harvest when grain moisture content is below 24%. Harvesting at higher moisture contents reduces total rice yield.
  • Head rice yield—Harvest between 17% and 24% moisture for maximum milling yield. Head rice yield declines if harvested at less than 17%. Avoid extended periods of time at 17%.
  • High harvest moisture—Harvesting at moisture contents above 24% requires aeration within a few hours to prevent off-odor development. The cost of drying is higher and total rice yield may be reduced.


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