In a recent article published in the journal Biology, Rachanat Limsomnuek and a team of researchers from Chiang Mai University examined how different farming methods impact the growth and health benefits of purple rice. The study specifically looked at the interaction between water levels, the use of rice husk biocharBiochar is a carbon-rich material created from biomass decomposition in low-oxygen conditions. It has important applications in environmental remediation, soil improvement, agriculture, carbon sequestration, energy storage, and sustainable materials, promoting efficiency and reducing waste in various contexts while addressing climate change challenges. More as a soil amendmentA soil amendment is any material added to the soil to enhance its physical or chemical properties, improving its suitability for plant growth. Biochar is considered a soil amendment as it can improve soil structure, water retention, nutrient availability, and microbial activity.   More, and various forms of nitrogen fertilizer. The researchers focused on the CMU K4 variety, a popular type of purple rice known for its high nutritional value and deep pigment. By testing these factors together, the team aimed to find the best combination for farmers to produce high-yielding, nutrient-dense crops.

The results of the experiment clearly showed that water management is a primary factor in determining how well purple rice grows. Rice plants grown in flooded conditions consistently outperformed those in non-flooded environments across almost every category. Specifically, flooded plants were taller, had more seeds per cluster, and produced a higher percentage of full, heavy grains. When flooding was combined with the application of rice husk biochar and fertilizers like urea or ammonium, the grain yield reached its peak. In contrast, using nitrate as a nitrogen source, especially in dry or non-flooded soil without biochar, resulted in the lowest productivity and poorest grain quality.

Beyond just the amount of rice harvested, the study found that these farming practices significantly changed the internal chemistry of the grain. Anthocyanins are the natural pigments that give the rice its purple color and provide powerful health benefits to humans, such as improving blood circulation and skin health. The researchers discovered that these beneficial compounds were most concentrated when the rice was grown in flooded conditions. Interestingly, while biochar helped increase the overall yield, its effect on the purple pigment was more complex, showing the highest concentrations when paired with specific fertilizers like nitrate or ammonium under flooded conditions.

The addition of rice husk biochar served as a powerful tool for improving soil quality. The biochar used in the study was highly alkaline and had a large surface area with many tiny pores, which allowed it to act like a slow-release sponge for fertilizers. Tests showed that when fertilizer was mixed with biochar and soil, it moved much more slowly than when applied to soil alone. This slow-release effect helps keep nutrients available to the plant for a longer period and prevents them from washing away. Even though biochar changed how the plants accessed nutrients, it did not negatively affect the visual appearance or the physical shape of the rice grains.

Ultimately, the study suggests that a three-part strategy of continuous flooding, rice husk biochar amendment, and the use of ammonium-based fertilizers is the most effective way to grow purple rice. This combination supports the plant’s natural physiology, leading to a 1000-grain weight and filled grain percentage that are superior to other methods. While the relationship between these factors and the exact nutritional content can be complicated, the evidence points toward flooded, biochar-enriched systems as a sustainable path for producing high-quality functional foods that meet the growing global demand for healthy rice varieties.

Source: Limsomnuek, R., Yamuangmorn, S., Jawana, R., Kamthai, S., Sanwangsri, M., & Prom-u-thai, C. (2026). Combined impacts of nitrogen forms, rice husk biochar, and water regime on purple rice yield and grain quality. Biology, 15(4), 349.