Methods of Straw
Incorporation - 92 



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Project Leader and Principal UC Investigators

Henry E. Studer, professor, UCD biological and Ag. engineering

Bryan M. Jenkins, assoc. professor, UCD biological & ag. engineering

Shirinivasa Upadhyaya, assoc. professor, UCD biological & ag. engineering


While growers are experimenting with a variety of methods to, incorporate rice straw into their fields, a team of UC Davis agricultural engineers is examining just how well some of these methods are working.

The scientists chose two adjacent farms near Pleasant Grove in Sutter County to conduct a study during .1992. Researchers sampled straw and stubble residue at each site both before and and after shearing stubble at soil level.

At the first plot, straw was chopped on a combine and spread as it exited the chopper. The residue was then stubble disked once in ,one treatment and twice in the other.

In the second plot, straw was spread by the combine without chopping. A field disc in tandem with a set of smooth steel cylindrical rollers ' mixed and packed straw into the soil. This plot was then moldboard plowed at a depth of 8-13 inches. In one treatment on the second plot the field was then disked with a spiketoothed harrow.


How well rice straw decomposes under different methods of incorporation is under study by agricultural engineers. One method, which involves the use of a cylindrical roller, was shown to be about 90 percent effective. As the illustration above suggests, this technique is also beneficial to waterfowl.

Since this project is still in progress, research findings are preliminary. However, researchers do note some significant trends. In the first plot they observed a "windrow" effect behind the combine, a clear indication that straw can be unevenly distributed behind a combine. These windrows were visible even after disking. As one might expect, residue amounts were higher where the straw was more heavily concentrated.

Before incorporation on this plot, straw and stubble averaged 8,260 pounds per acre, After one disking, surface residue averaged about 2,500 pounds per acre. A second disking did not produce a substantial improvement.

In the moldboard plowing plot, straw and stubble averaged 6,840 pounds per acre. After plowing: 370 pounds per acre: After plowing and disking: 478 pounds per acre.

The researchers' preliminary conclusion is that straw incorporation by the chopping and disking technique is about 75 percent effective, while the spreading, rolling and moldboard plowing approach was about 90 percent effective. The engineers also note that distribution of the straw is a function of how the discharge vanes of the chopper are adjusted and is therefore under the control of the combine operator..


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