Overview

Rice is primarily grown in two regions of the United States: the Sacramento-San Joaquin Delta region of California and the Mississippi River valley states of Arkansas, Louisiana, Mississippi, Texas and Missouri. The largest share of planted acres is in Arkansas, with 48% of rice acres in 2020. The summary chart shows overall consistent improvement in land use and GHG emissions, with improvement in irrigation water use recently plateauing, and mixed results for energy use (Figure 1.7.1). A summary of all indicators for rice for reference years is presented in Table 1.7.1. Figure 1.7.1. Summary chart of indicators for rice during 1980-2020 Data are presented in index form, where all indicators have been scaled by indicators averages for the period 1998-2002. A 0.1 point change is equal to a 10 percent difference. Index values allow for comparison of change across indicators with different units of measure. A smaller area represents improvement over time. Additional illustrations of rice sustainability on a per acre basis and for total resource use are available in Appendix B, accessible from the Download Report link.

Land Use

Land use in rice production in the U.S. has stayed relatively steady over the study period (Figure 1.7.2). Production increased from 1990 to 2005, and the trend has since leveled off (Figure 1.7.3). The land use efficiency indicator demonstrates increases in yield, showing improvement throughout the study period until decreasing in recent years (Figure 1.7.4).

Energy Use Efficiency

Energy use efficiency for rice production improved in the 1980s and the 2010s but decreased in the 1990s (Figure 1.7.5). On a per acre basis, energy used for rice production increased from 1980 until around 2010, when it began to decline (Figure B.25). The largest energy component for rice is fertilizer use, followed by irrigation (Figure B.26). Increases in the amount of fertilizer applied, therefore, are largely driving the increase in energy use.

Greenhouse Gas Emissions

GHG emissions per unit of rice production declined through the 1980s, plateauing through the 1990s, then continued declining after 2000 (Figure 1.7.6). Emissions per acre had a moderate rate of increase from 1990 up to 2010, when it shifted to a slightly downward trend (Figure B.27). The primary component of emissions for rice is methane, consistently contributing over 80% of GHG emissions for this study, which results from anaerobic soil conditions in flooded fields. These emissions have increased slightly from 1990 to present, although emissions on a per unit of production basis have declined due to increasing crop yields (Figure B.28). The top four contributors for rice for energy use and GHG emissions during 2010 to 2020 are listed in Table 1.7.2.

Irrigation Water Use

Irrigation water use efficiency for rice has also improved across the study period, with the greatest improvement occurring from 1980 to 2010 (Figure 1.7.7). In the early 2010s, there was a period of lower irrigation water use efficiency, although in recent years, it has again improved to the level of 2010. Research in Arkansas indicates increasing adoption of water conservation practices, including intermittent flooding and row rice production (Hardke et al., 2021); however, data are not collected on such practices at the national scale. Reduced flooding time for rice fields also has a significant impact on methane emissions, and it will be important to capture the extent of such practices in future editions of this report (Linquist et al., 2018).

Soil Erosion

Rice is produced on flooded fields that are managed to have little to no slope in order to retain water. As a result, rice fields are generally less susceptible to soil erosion. The soil erosion indicator shows generally static, low levels of erosion throughout the study period (Figure 1.7.8), with erosion values ranging from 1.8 tons to 2.1 tons of soil loss per acre per year from rice-producing fields. Download Rice Data