Rice Straw Management
Rice straw has been burned as the primary method of disposal since the beginning of the California rice industry. Rice straw interferes with soil preparation, causes several crop problems (including diseases), and may delay planting. The cheapest, fastest and most effective method of straw disposal is burning (fig. 31). With little market demand for rice straw and the higher cost of soil incorporation, there has been little incentive for rice growers to quit burning. However, smoke from rice straw is increasingly objectionable to many residents of the Sacramento Valley.
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Figure 31. The cheapest, fastest, and most effective method of straw disposal is burning. |
The Rice Straw Burning Reduction Act of 1991 mandated a reduction in rice straw burning, accomplished through a scheduled phasedown, according to the following schedule:
Table 3. The Rice Straw Burning Reduction Act (AB 1378). |
The Rice Straw Burning Reduction Act of 1991 provides for the gradual phaseout of rice straw burning in the Sacramento Valley by the year 2000, as shown below. The number of acres eligible for burning declines annually until the prohibited amount reaches 100%. However, a "safe harbor" clause in the law allows for up to 25% burning annually for disease control, after the year 2000. By gradually reducing burning, the law's intent is to allow time for the development of alternatives, including the in-field and out-of-field methods. Most growers initially have used soil incorporation because there are few economical or widespread uses for rice straw. |
| Year |
Permitted Acreage |
| 1992 |
90% |
| 1993 |
80% |
| 1994 |
70% |
| 1995 |
60% |
| 1996 |
50% |
| 1997 |
38% |
| 1998 |
25% |
| 1999 |
25% |
| 2000 |
Conditional only |
The ordinance pertains to rice straw in the Sacramento Valley only, and does not impact burning of other crops or rice in other areas of California. The intent of the law is, in as much as possible, to gradually eliminate burning and to allow the rice industry time to find economically viable alternatives to burning. At the end of the phase-in there is a "safe harbor" provision to allow conditional burning for rice disease management on a maximum of 25% of the acreage in any given year.
Non-burn alternatives include soil incorporation and off-field utilization. Few commercial viable markets exist so most rice straw is soil incorporated. Soil incorporation practices vary greatly, but can be conveniently categorized into two major methods. Non-flooded systems depend on winter rainfall for moisture and straw is incorporated in the fall with tillage implements (fig. 32). The straw may or may not be chopped before it is incorporated with discs, chisels or plows. The degree of straw decomposition is mainly determined by rainfall and temperature and to some extent grower management practices. Consequently, decomposition rate will vary from year to year.
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| Figure 32. Non-flooded fall straw incorporation using conventional disk. |
The winter-flooded system differs in that floodwater is introduced to the field shortly after harvest is completed and maintained until spring. The straw may or may not be prepared by chopping or soil incorporating before flooding. After flooding, many fields are rolled with specially built "cage rollers" which help create soil/straw contact (fig. 33). Decomposition of straw in this system is not limited by moisture and has consistently given more complete decomposition compared to non-flooded systems.
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Figure 33. A custom built cage roller is used to press straw to the soil surface to improve contact in a flooded field. High moisture and warm fall temperatures accelerate straw breakdown after harvest. |
Experience to date suggests that the major concerns regarding rice straw incorporation are related to 1) crop effects that potentially reduce yield, 2) physical inability to consistently incorporate large acreage in a timely manner, and 3) added cost, currently about $36/acre on average, of straw which does not generate additional income. For these reasons, alternatives to incorporation are highly desirable.
Most potential uses of rice straw can be categorized into energy use, manufacturing and construction, environmental mitigation or livestock use. For example, energy products may include ethanol, methane, heat for electricity and producer gas from gassification. Manufacturing includes a range of pressboard, fiber/waste plastic, paper pulp and fiber/cement products. Direct use of rice straw bales for construction of dwellings and other structures is also possible. Environmental mitigation uses include the use of rice straw for erosion control on construction areas or for rehabilitation on burned slopes. Small amounts of rice straw are used in composting, mushroom production, and livestock feed and bedding.
There are many potential uses of rice straw yet few are currently being used. The reasons appear to be related to 1) technical constraints, 2) economic feasibility, particularly related to the cost of removing straw from the field, and supply and storage problems.
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