Rice Utilization and Product Development, 2011

 

Project Leader

Zhogli Pan, research engineer, USDA Agricultural Research Service, Albany, CA

The California rice industry needs an updated universal “shrink chart” to more accurately assess dockage and moisture changes in dried rice.

Rice is harvested at moisture levels that require drying for safe storage. Moisture removal reduces rice weight. Additionally, material other than grains is in harvested rice. To account for these factors, the final dried weight is docked. Dockage is typically assumed to be 2% of harvested rice.

However, harvesting and handling technology have greatly improved, thus lowering actual dockage. Additionally, weather events, especially rain and wind, influence harvesting operations and could affect dockage. The goal of this research was to clarify and quantify factors that influence rice dockage and to update the rice shrink chart.

Previous research from 2010 reported on the impact of rice variety, harvest moisture, harvesting date, drying and dropping from certain heights, and rice growing location. Research conducted during the 2011 rice-harvesting season focused on the impact of harvester type and weather events on rice dockage.

Rice of medium grain varieties M104, M202, and M206 were procured weekly for up to seven weeks from specific rice growers with different harvesters and farms near Arbuckle and Grimes. Four popular models of rice harvesters with different headers were used in this research—John Deere with stripper header, Case IH with conventional header, John Deere with conventional header, and Claas Lexion with conventional header.

During rice harvest season, changes in weather events were monitored and rice samples were collected from the harvesters to study the impact of wind and rain on dockage. Additional rice samples were obtained from Farmers Rice Cooperative in accordance with last year’s procedures to confirm the repeatability of results. Moisture content of freshly harvested rice used in this study ranged between 18% and 26%.

Results from the study indicate that dockage of freshly harvested rice varied, on a wet basis, between 0.2% and 2.0%, with an average of 0.79% (0.92% in 2010). Similarly, mean value of dockage of dried rice with 14% moisture content was 0.65% (0.78% in 2010).

There were no significant differences in dockage among rice varieties. Results were consistent with 2010 results. No significant relationship was found between dockage and harvest moisture content. Wind and rainfall events, however, significantly increased dockage—0.9% on windy days, 2.0% for rain events compared to normal weather conditions (0.6%).

The type of harvester and header also affected dockage, with the stripper header indicating less dockage (0.5%) compared to the conventional header (up to 0.8%). The stripper header combs rice out of the rice head, leaving whole stalks still standing—unlike conventional headers that gather stalks and chaff.

The average value of dockage for freshly harvested rice was 0.9%, significantly lower than the widely accepted value of 2%. This value can be used to update the rice shrink chart. Proper consideration should be given harvester, header type, weather conditions, and other factors that influence dockage.

Impact of harvester and header type on dockage of freshly harvested rice samples


Impact of harvester and header type on dockage of dried rice samples