|Disposal of Rice Straw by Soil
Incorporation - 84
The long-established practice of disposing of rice straw by burning is an increasingly worrisome problem both to rice growers and their urban neighbors. An obvious alternative. to burning is incorporating the straw into the soil. Long before the rice marketing order was established, UC studies in cooperation with the Rice Experiment Station indicated no differences from burning or incorporating the straw on subsequent rice yields.
This research, however, did not address two grower concerns: 1) how to incorporate up to 3 1/2 tons per acre of long loose straw into heavy rice soils; and 2) the effect continued straw incorporation might have on the buildup of diseases, mainly stem rot.
One of the first problems addressed after growers approved the rice marketing order in 1969 was how to incorporate the long straw of the tall varieties. UC agricultural engineers tried shredding, chopping, and spreading the straw to make it easier to disk or plow under. The most successful procedure was to chop the straw with the shear-bar type forage harvester modified with a simple spreader attachment to distribute the chopped straw uniformly. Impact-type rotary cutters and shredders were not adequate, especially with high moisture straw. The costs in equipment, energy, and time are high. The operation also comes at the time fall rains begin.
Trials on the mechanics of incorporating chopped straw were conducted in 1971-72, an abnormally dry year, and in 1972-73, a wet year. The work was done on two farms, one in Colusa County and the other in Sacramento County. Incorporation after chopping with the shear-bar chopper was satisfactory on two different soil types using the same operations between harvesting and planting that normally are used after burning. The only added cost for straw incorporation was the cost of chopping. If the straw is not adequately chopped, however, several extra diskings are required.
Limited tests with a special moldboard plow which had a shallow cutting unit ahead of each moldboard bottom indicated that this plow covered the straw better than the conventional moldboard plow but that it required prohibitively large increases in energy.
Although experimental plots have not shown yield losses to stem rot disease from straw incorporation, the buildup of inoculum is encouraged by incorporation, and the disease does depress rice yields. It is quite possible that the small plots used for experimental work do not represent conditions in large fields.
Straw incorporation remains to be a very unpopular treatment with rice growers because of the added costs and the increased incidence of disease.