Two methods have been tested for modifying the windrow in an attempt to reduce grain damage that appears to be associated with repeated drying and wetting influenced by humidity and dew.

A modified swathing process that positioned the grain in the center of the windrow between layers of straw was studied in 1985. A mechanically simpler method that involves covering the windrow with a layer of stubble cut from either side of the windrow was tested in 1986 and 1987. The latter method also does not appear to significantly affect harvester capacity or drying rate in the windrow, reduces grain loss associated with handling of windrows, yet maintains higher head rice yields compared to open windrows over all moisture contents, and higher head rice yields than direct-harvested medium-grain rice at low moisture.

Comparison of harvesting techniques in 1987, using the variety M202, indicated head rice yields of 43 percent at day 17 for grain in treated windrows, and 42 percent at day 18 for direct-harvested grain. Grain moistures at harvest were 10 percent for the treated and open windrows and 16.6 percent for the direct-harvested grain.

Grain dried rapidly in both types of windrows, reaching 14 percent moisture in three days. Head rice yields dropped most rapidly during the first six days after swathing, decreasing from an initial 65 percent to 37 percent in the open windrows and from 65 to 47 percent in the covered windrows during this interval. However, the open windrows continued to decline at an accelerating rate, while the covered windrows continued to decline at a decelerating rate.

Swath Harvesting Shows Economic Potential

An economic model that considers harvesting, transportation and drying costs was developed to compare direct and swath harvesting techniques.

An analysis using the model to compare direct harvesting with the modified swath technique tested in 1986 and 1987 showed that net profit could be increased six percent by using modified swath harvesting. Although harvesting cost increased by 50 percent as a result of lower equipment capacity and added cost of the swather, drying and transportation costs were reduced 64 percent and 7.5 percent, respectively, by swathing. Net value of the grain was only slightly greater (0.2 percent) for swath harvesting due to a slightly greater head rice yield.

Basic assumptions for the analysis included a starting moisture content of 24.5 percent for direct harvesting and a 30 percent moisture content (maturity) for swath harvesting. Individual field size was 250 acres, with a total acreage of up to 1,250 acres. Harvest time was assumed to be 11 days for direct harvest and 12 days for swath harvesting. The extra day for swath harvesting was attributed to lower field efficiency and shorter header width on the swather. Swath harvesting was complete 12 days after maturity, whereas direct harvesting was complete 15 days after maturity (due to waiting four days after maturity to reach desired beginning grain moisture content). Moisture content at the end of direct harvesting was 17.6 percent. All grain delivered under swath harvesting was assumed to be less than 14 percent.

Economies of scale and optimum harvesting operations also were calculated using the model and the above assumptions.

As the size of the harvest increased, the economic advantages of modified swath harvesting increased. Only very small-scale operations indicated a slight advantage for direct harvesting.

When only one harvester is used on a block of 250 acres, the model indicates that the optimum approach for direct harvesting is to begin immediately after grain maturity, as increased head yields will offset increased drying costs. However, imposed upper limits on moisture in grain delivered to the dryer may require starting the harvest at lower than optimal grain moisture. When harvest begins at grain moisture less than 27 percent but above 21 percent, the model indicates that two harvesters are preferred, with increased head rice yields resulting from faster harvest offsetting the additional financial cost of another harvester. Below 21 percent moisture, the added financial cost cannot compensate for the loss in value due to the rate of decline in head rice, and a single harvester is again preferred.
 

Swath Harvesting Promotes Field Drying Researchers had experimented with harvesting rice into windrows as early as the 1930s, but they encountered the same problem, project leader Bryan M. Jenkins did initially - "a severe degradation of quality." Left vulnerable to the night sky, dew would collect on the exposed grain. The result: fissuring, cracking and breaking. UC Davis agricultural engineer Bryan Jenkins examines the portable weather monitoring station that records baseline data needed for his research. Several years ago Jenkins, an agricultural engineer at UC Davis, came up with the idea of folding windrows, which sandwiches the grain in the middle of a protective layer of straw. "The problem is it's difficult to perform mechanically," Jenkins said. In 1987 Jenkins tried something different at Heidrick Farms in the Yolo bypass. He hooked up a modified flail chopper to a tractor and whacked the stubble down to about three or four inches. But rather than dump the stubble out the back, the discharge spout was placed over the windrow to lay down a fluffy two-inch layer of stubble on top of the grain. That was enough to protect the rice and yet allow it enough circulation with the air to dry out. The technique saves on drying costs, allows the opportunity to get into rice fields sooner and thereby reduce the number of harvesters required, and, because the rice can be transported at a lighter weight, fewer trucks are required at harvest. The only drawback to the system might come from an early rain. "The windrows, once wet, might be more difficult to thresh than standing grain," Jenkins said. The researcher is working on incorporating the chopper and swather together, so only one pass would have to be made through a field. He anticipates commercial application within a year.