Changing straw management practices in California rice fields: A recent and historical analysis of the Sacramento Valley

Abstract

Agricultural practices are constantly evolving due to changes in regulation, climate, and technology. Regulations in California resulted in phasing out rice ( Oryza sativa L.) straw burning in the 1990s, leading to a range of alternative practices to manage the straw, which impact agronomic practices, air quality, ecosystem services, and wildlife habitat. It is important to understand how these practices change over time. To address this, we conducted post‐harvest surveys during the winters of 2016/2017 and 2017/2018. We visually observed 1146 fields representing about 8% of the total rice area to determine the straw management practices implemented (unmanaged, burn, bale, chop, or incorporate) and winter irrigation (flooded or non‐flooded). We also compared these results to historical data. Over 2 study years, an average of 52% of fields were flooded. In all fields, straw incorporation was the primary practice used. Comparing these findings to previously published data, the largest changes were documented in two practices between the 1980s and 2007. Burning dropped from as high as 40% (1980s) to <2% (2007 onward), in contrast, flooding increased from <16% to over 40%, respectively. From 2007 to 2018, there were no major changes to post‐harvest field management and those that were observed could be attributed to the amount of fall rainfall. Despite little change to the relative proportion of practices used, the area planted to rice changed significantly (>25%); thus, the area under each practice changed considerably. This has important implications for winter water allocations, greenhouse gas inventories, and wildlife habitats.