RICE STRAW MANAGEMENT
Traditionally, rice fields were burned after harvest to dispose of the left over straw and to control disease and pest problems that can carry over between crops. Crop burning can be an effective tool that is used for a number of orchard and field crops. Unfortunately, the burning also produces many pollutants, impacting the air quality of the Central Valley region during burn season. State legislation was passed to significantly reduce the practice of rice burning between 1990 and 2000, to address these air quality concerns. This left rice growers to find alternative ways to manage the rice straw that remains after harvest. Three primary ways of managing rice straw in the post-burn era are: (1) incorporation of the straw into the soil coupled with active winter flooding, (2) straw incorporation without active winter flooding, or (3) harvesting the rice straw for use in other industries. Figure 11 shows the percentage reduction in burned acres and increase in the use of other practices that occurred between 1990 and 2000, primarily driven by the phase-down legislation.
The emission of regional air pollutants from rice has been significantly reduced from 1980 to 2010. An estimate of air pollution impact from rice production includes the emissions from open burning of rice as well as emissions from fuel combustion in equipment used to grow, transport, and process the rice. The emissions from uncontrolled burning dominates these other sources of emissions. Figures 12-14 shows the overall reduction levels for criteria pollutants including NOx (oxides of nitrogen, ozone and particulate precursor), VOC (volatile organic compounds, ozone precursor), and PM (particulate matter, direct pollutant) per unit of rice production over the thirty year time period. These pollutants have all been reduced by 80-90% in the last 30 years.
Figure 11. Straw Management Practices in California Rice. 1980-2010
Figure 12. NOx Emissions from California Rice Production. 1980-2010
Figure 13. VOC Emissions from California Rice Production. 1980-2010