Objective

• Determine the technical feasibility for a system of swath harvesting rice prior to combining that would improve head rice yields.

The UC Department of Agricultural Engineering in past years has engaged in research with Rice Research Board support on straw incorporation, straw handling, rice harvesting, and utilization of rice straw for energy generation. Straw incorporation, although technically possible, has many problems that make it unattractive to growers. A process to generate energy from rice straw has been developed but is not economical at current energy costs. A study comparing raspbar and spiketooth cylinders in rice combines showed no clear-cut differences between them. For the past two years, engineering research has focused on a procedure for swath harvesting rice prior to combining as a possible way to increase head rice yields.

In 1985 studies, significant increases in head rice yields were obtained by folding part of the windrow over to cover virtually all of the panicles from exposure to the sun while drying and from dew at night. The 1986 studies compared open windrows from swathing with windrows covered with closely harvested stubble.

 

Figure 4. Head rice yields from covered and open swaths when harvesting occurred from one to nine days after swathing.

Ten treatments were compared; half were open windrows and half were covered with rice stubble cut from either side of the windrow. For each treatment, drying times in the windrow from swathing to harvest were 1, 3, 5, 7 and 9 days. Grain samples were taken at harvest time and analyzed for moisture content, total milled rice yield, head rice yield and several other characteristics.

Head rice yields for covered and open swaths for different field drying times are presented in Figure 4. Although head rice yields among samples from the same treatment varied, head rice yields declined with time for open windrows but not for the stubble-covered windrows. Differences in head rice among drying times for covered swaths were not statistically significant. Differences between open and covered swaths were significant at five days and beyond.

Essentially no differences in moisture content of the grain were observed between the covered and open swathing treatments at the time of combining. The drying rate for open and covered windrows was the same, with most of the drying occuring during the first three days. Straw moisture contents between open and covered windrows were essentially the same. There appeared to be more threshing loss from the covered windrows, perhaps because of more straw passing through the harvester.

The windrow folding treatment studied in 1985 and the stubble covering treatment used in 1986 appear to reduce environmental stress on the grain. Both techniques are superior to open windrows after prolonged exposure in the field.

Indications are that it is technically feasible to maintain grain quality in a windrow with prolonged exposure in the field. For covered windrows, moisture content at harvest could not alone be used to predict head rice yield, as this yield was unchanged from 25 to 14 percent moisture at harvest and was consistently higher than the yield for open windrows. The economic feasibility of using folded or stubble covered windrows has yet to be determined.