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A comparative assessment of polymer-coated and non-coated urea in direct-seeded rice: agronomic, economic, and environmental performance and sensitivity analysis
Summary
A field and modeling study in Japan compared polymer-coated urea (slow-release fertilizer wrapped in plastic capsules) with conventional urea, finding that despite the plastic pollution cost of the capsules, the coated fertilizer had a lower overall environmental cost because it reduced nitrogen runoff losses. However, the authors note that the environmental cost of microplastic pollution from the capsules is highly uncertain because the ecological harm of agricultural microplastics is still poorly understood. If alternative low-loss nitrogen application methods achieving over 50% nitrogen recovery can be developed, they could replace coated urea without the plastic pollution trade-off.
The application of polymer-coated urea (PCU) to crops is likely restricted because the product's capsules cause plastic pollution. Although conventional fertilizer use reduces plastic pollution, it may increase nitrogen (N) pollution owing to its lower N recovery than that of PCU. Therefore, we need to develop optimal N application methods to reduce both plastic and N pollution. Here, we aimed to (1) compare the agronomic, economic, and environmental outcomes of PCU application with those of conventional urea application and (2) provide quantitative targets for developing alternatives to PCU application in dry direct-seeded rice production. We developed a model incorporating yield, brown-rice protein content, farmer profit, and environmental damage cost due to N and polymer losses according to N fertilizer application. Data were collected from field experiments at a farm in Iwate, Japan from 2020 to 2022. The average apparent N recovery was 0.43 for PCU and 0.37 for conventional urea. Despite the plastic damage cost, the estimated total environmental cost of PCU was lower than that of normal urea owing to the former's higher N recovery. However, our ability to simulate plastic pollution is limited, as few of the environmental effects of microplastics are understood. If new N application methods with N recovery above 0.5 are developed, an N fertilization cost within $5 × 10 −3 g −1 N can maintain the same benefit as that obtained in the current simulation. This model can be used to evaluate the quantitative relationships among N recovery, benefits, and implementation costs of each candidate N application method.
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