11
Sep
Organic Rice Offers Greater Biodiversity Support than Chemical-Intensive Paddies, Study Documents
(Beyond Pesticides, September 11, 2025) A study published in Agriculture, Ecosystems & Environment finds organic rice paddies in the Mediterranean region have greater ecosystem biodiversity, including increased presence of aquatic microorganisms and insects, than their chemical-intensive counterparts. While not a “cradle-to-grave” or holistic analysis of organic vs. chemical-intensive agriculture (see a similar example in previous Daily News here), the authors note that there is an increase in greenhouse gas emissions (GHGe) associated with compost use, which replaces synthetic fertilizers. Typically, compost builds biological life in the soil and contributes to a drawing down (or sequestering) of atmospheric carbon. As EPA notes, “[C]omposting lowers greenhouse gases by improving carbon sequestration in the soil and by preventing methane emissions through aerobic decomposition, as methane-producing microbes are not active in the presence of oxygen.”
The transition to organically produced rice in the U.S. has come with challenges. One includes thorny debates over the inclusion of copper sulfate on the National List of Allowed and Prohibited Substances, which establishes materials permitted for use in certified organic production under the Organic Foods Production Act (OFPA). Under the law, USDA restricts copper sulfate in organic farming as follows: “For use as tadpole shrimp control in aquatic rice production, use is limited to one application per field during any 24-month period. Application rates are limited to levels which do not increase baseline soil test values for copper over a timeframe agreed upon by the producer and accredited certifying agent. For use as an algicide in aquatic rice systems and for tadpole shrimp control in aquatic rice systems; use is not to exceed one application per field during any 24-month period. Application rates are limited to those which do not increase baseline soil test values for copper over a time frame agreed upon by the producer and accredited certifying agent.” (Reference: 7 CFR 205.601(a)(3), 205.601(e)(4), & 205.601(i))
Certifiers of organic are charged with evaluating the need for copper sulfate use and determining that other preventive means, including cultural practices, have been tried.
It should be noted that copper sulfate, like all allowed substances in organic, is subject to public review and comment on a five-year cycle and must be reviewed by the National Organic Standards Board (NOSB) and voted on to remain on the National List. In chemical-intensive agriculture, by contrast, copper sulfate is registered for use as a fungicide, algicide, a source of copper in animal nutrition, as fertilizer and herbicide, and for seed treatment. It is also used to kill slugs and snails in irrigation and municipal water treatment systems.
As biodiversity, public health, and other planetary boundaries strain under the weight of a fossil fuel and chemical-intensive global economy and society, organic advocates continue to call for the incorporation of climate resilience into organic agriculture with improved soil biology and water retention.
Background and Methodology
The study was conducted in Albufeira Natural Park (ANP), a wetland listed under the intergovernmental treaty Ramsar Convention on Wetlands of International Importance since it is considered “a key ecological and economic resource in the region.” There are four sampling sites—a water spring (on the edge of ANP and consisting of aquatic plants [macrophytes]), an organic rice field (manually seeded and fertilized with horse manure), and two chemical-intensive rice fields. The first chemical-intensive rice field, located in the northern area of ANP, was irrigated with reclaimed wastewater and used more pesticides due to issues with weeds, pest pressures, and a seed variety prone to fungal disease. The second chemical-intensive rice field is in the southern area, and it was irrigated with water from Albufera Lake. Researchers gathered three samples from each site throughout the 2021 cultivation cycle, with more specific information on the seeding dates, irrigation regimes, pesticide and fertilizer applications, and drying periods available to review in Section 2.1 of the Materials and Methods section.
The researchers emphasize the significance of this study, given that there has generally been minimal research “explor[ing] the long-term effects of pesticides and conventional rice farming practices—such as intermittent drainage or fertilization—on biodiversity in rice paddies.” In this vein, the researchers reference previous studies suggesting the benefits of organic rice farming (see here, here, and here), however these were all conducted in subtropical regions in Asia; Mediterranean rice paddies, meanwhile, have specific management practices that significantly affects the GHGe [greenhouse gas emissions] of rice production, “such as post-harvest flooding patterns, straw management, and the type of wetlands previously present on reclaimed land.”
In terms of gathering data on aquatic organisms, researchers engaged in biological sampling and analysis for microbial communities (bacteria and archaea), zooplankton, macroinvertebrates, and emerging insects. Gathered through water and sediment using an EZNA soil DNA kit, researchers tested for phylogenetic diversity (which is considered a measure of biodiversity between species rather than just relying on a given species’ abundance or quantity). Only individuals from the microzooplankton group were gathered after the researchers identified them through a stereomicroscope, filtering samples through 5 liters of water through a zooplankton net. Macroinvertebrates were gathered through a net, preserved in 96 percent ethanol, and biomass measured after drying the samples and removing shells from the assessment. Emerging insects went through a similar sampling process, except that pyramid-shaped nets were used. To test GHG emissions (specifically carbon dioxide and methane), researchers used a tactic employed in previous wetland studies to gather sediment cores to assess the exchange of CO2 and CH4 gases between May and October 2021. More information on the statistical data analyses employed in this study is available for review in Section 2.5.
The authors are based at universities in the European Union, including the University of Alcala, IMDEA Water Institute, and University of Valencia. They declared that “they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.” The study received funding from the Spanish Ministry of Science, Innovation, and Universities, Agency of Research, and Recovery and Resilience Facility (which “finances reforms and investments in EU Member States made from the start of the pandemic in February 2020 until 31 December 2026).
Results
“The study….reveals that the structure of aquatic communities is heavily influenced by rice farming practices, with organic rice farming supporting a larger abundance of pollution-resistant zooplankton and a higher diversity and biomass of emerging insects,” says the authors. They continue: “However, organic rice farming was associated with the highest prevalence of fecal microorganisms and contributed more to greenhouse gas emissions during the rice cultivation period due to its manure fertilization regime.”
Key patterns that the authors note for the organic rice field are that it is characterized by higher biodiversity (particularly for insects), higher presence of fecal-associated microbial life (which the authors warn may be “indicating a potential risk of pathogen introduction through manure-based fertilization”), and higher GHGe overall from manure. “Higher insect emergence in the Organic Rice field provide[s] food to riparian arthropod predators, amphibians, and water birds, contributing to energy transfer between aquatic and terrestrial environments,” say the authors. When calculating GHGe, the authors do not consider the emissions associated with synthetic fertilizer production – they only measured the flux of methane and carbon dioxide from the sampling sites and assessed the difference in emissions and potential for carbon sequestration.
Meanwhile, the two chemical-intensive fields generally have low biodiversity, higher presence of aquatic life that are “pollution-tolerant,” and contain moderate-to-high GHGe depending on the water source for irrigation. It is important to note that daily methane emissions were highest in the first conventional rice field relative to all other sites. They also emphasize that “GHG emissions observed in this study are relatively low compared to those reported in other regions.” There are practices identified “to mitigate methane emissions, such as delaying winter flooding or removing straw after harvest to reduce methanogenesis and microbial decomposition, which are key contributors to elevated CH₄ and CO₂ fluxes, respectively.”
Previous Research
As this study lays out in its introduction, there is significant research on the impacts of rice production on ecosystem health and broader biodiversity.
A study published in 2022 in Communications Biology finds that ‘Weedy rice,’ a close relative of cultivated rice that invades rice fields and reduces yields, is rapidly developing herbicide resistance in critical rice growing areas throughout the United States. Researchers note that the root of the issue farmers face is a result of an agricultural approach that relies on a single, streamlined method of weed control. “Just like in the case of antibiotic resistance, the rise of resistance to this particular herbicide will be met with a new technology that relies on a new herbicide,” says study co-author Marshall Wedger, PhD. He continues: “New herbicide-resistant cultivars are already in development, so I expect this process to repeat.”(See Daily News here.) Similar issues have emerged with herbicide- and pesticide-resistance, including waterhemp (Amaranthus tuberculatus), commodity crops like corn, and other “crops” like farm-raised fish and the sea lice pesticide emamectin. More specifically to rice production, a 2016 study published in Scientific Reports and produced by Japan’s National Institute for Environmental Studies found that the insecticide fipronil significantly reduces the population of adult dragonflies, more so than any other pesticide treatment. (See Daily News here.) This is also a potential public health crisis, as a Consumer Reports-published study in 2012 found “worrisome” levels of inorganic arsenic in rice products across organic and conventional products, challenging advocates to meet this moment of crisis and call for alternatives while also continuing to be critical. (See Daily News here.)
One of the more controversial inclusions to the National List of Allowed and Prohibited Substances is that of copper sulfate. As an antimicrobial and fungicide, its use is permitted in organic certified operations for food/feed crops, including orchard, row, field, and aquatic crops, flowering/non-flowering plants, and trees. Beyond Pesticides has continued to call for the sunset of this material, given the known associated adverse health and ecological effects. (See here for Beyond Pesticides’ comments to the National Organic Standards Board).
The authors of a 2024 case study in Canale D’Aiedda (Italy) published in Scientific Reports, conclude that, “[T]he results of monitoring and modeling activities revealed a chronic risk associated with the presence of Cu [copper] from November to April in several river reaches and acute risk associated to the presence of glyphosate in several reaches mainly in the wet season.” According to the authors, “The most important factor influencing the chronic risk for Cu were the combination of two factors: the high surface runoff and the Cu applications. The most important factor influencing the glyphosate peaks of concentration is the streamflow.” The NOSB has previously discussed alternative growing systems that would eliminate the need for copper sulfate and made such alternatives a research priority. Copper sulfate is widely used in organic rice production to control algae and an invertebrate known as tadpole shrimp. Most of the world transplants rice seedlings into flooded paddies. Dryland rice production eliminates the need for control of tadpoles, which eat the rice seedlings in flooded fields. Ironically, tadpole shrimp are regarded as a biological control for algae. (See Daily News here.)
Call to Action
There is a concerted effort in Europe to advance what is being coined as Organic Climate Farming. As organic is increasingly understood to be a climate solution, OrganicClimateNet last year launched an aggressive effort to build the base of organic farmers in the European Union (EU). (See Daily News here.) OrganicClimateNet defines organic climate farming as “an agricultural approach that integrates organic farming’s nature-based and circular principles with climate-conscious practices. This combination provides innovative and impactful solutions to the challenges posed by climate change.
You can take action today by leveraging and sharing Eating with a Conscience, which is a repository including dozens of non-organic fruits, vegetables, and food items to see which pesticides can be used in their production. There are specific sections on rice and wild rice that may be relevant; however, this tool was developed to help you evaluate the impacts on the environment and farmworkers of the toxic chemicals allowed for use on major food crops, grown domestically and internationally.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
