Their findings reveal that while monsoon-season rice shows limited yield response to N inputs, dry-season irrigated rice can nearly double its yield when nitrogen is applied judiciously. By integrating agronomic trials with economic assessments and social-cost analyses, the study demonstrates that optimized N rates can boost farmer profitability while sharply reducing reactive nitrogen pollution from rice paddies.
Rice production in Myanmar remains constrained by low inputs, inadequate access to agronomic knowledge, and poor infrastructure, leaving many farmers trapped in a cycle of low productivity and low returns. Although Myanmar is one of Southeast Asia’s largest rice producers, fertilizer use has traditionally been limited, resulting in high greenhouse gas emissions per unit of rice and inefficient nitrogen recovery. Previous studies have also shown that excessive nitrogen use can degrade soil nitrogen-cycling processes and accelerate losses of reactive nitrogen (Nr), which are associated with climate impacts and water pollution. These challenges underscore a dual problem: monsoon rice receives more nitrogen than it can effectively utilize, while dry-season rice receives too little.
A study (DOI:10.48130/nc-0025-0009) published in Nitrogen Cycling on 11 November 2025 by Xia Liang’s & Deli Chen’s team, The University of Melbourne, reports the discovery of nitrogen application rates that maximize economic returns while minimizing ecological and social costs in monsoon and dry-season rice systems.
The research team employed an integrated approach combining multi-year field experiments, microbial nitrogen-cycling assays, farm-level economic surveys, and simulations from a calibrated Water and Nutrient Management Model (WNMM) to assess how nitrogen inputs influence rice yields, soil nitrogen processes, and reactive nitrogen losses across monsoon and dry-season systems in central Myanmar. Field trials quantified yield responses to incremental nitrogen additions for both seasons, while laboratory measurements—using acetylene reduction calibrated against 15N₂ fixation and 15NO₃⁻ conversion—evaluated microbial contributions from biological nitrogen fixation and dissimilatory nitrate reduction to ammonium (DNRA). By comparing long-term low-input paddies (≤25 kg N·ha⁻¹ historically) with high-input paddies (>100 kg N·ha⁻¹ over 5–17 years), the study directly examined how fertilizer regimes affect microbial activity and nitrogen availability. Complementary economic analyses, based on data from roughly 600 smallholder farmers, incorporated fertilizer prices, labor costs, and market rice values to estimate two investment benchmarks: ROI-100 (100% return on investment) and ROI-0 (where marginal revenue equals marginal cost). These benchmarks were used to determine season-specific economically optimal nitrogen rates. The WNMM model further quantified nitrogen loss pathways—including NH₃ volatilization, N₂O emissions, and NO₃⁻ leaching—and translated them into social pollution costs using regionally adjusted damage values derived from EU and US studies. Results showed strong seasonal contrasts: monsoon rice exhibited limited yield gains beyond ~45–83 kg N·ha⁻¹, while dry-season rice responded robustly up to ~202 kg N·ha⁻¹. Ecological optimization recommended substantially lower rates—66 kg N·ha⁻¹ for monsoon rice and 48.2 kg N·ha⁻¹ for dry-season rice—which significantly reduced reactive nitrogen losses while maintaining reasonable economic returns. Adopting these ecological rates could save US$55–368 per hectare annually in pollution costs, and farmer workshops indicated high interest in social-media-based decision tools to support improved fertilizer practices.
By defining both economic and ecological nitrogen optima, the research offers clear evidence that fertilizer use can be rationalized without compromising food security. Future work will focus on scaling participatory decision-support approaches—particularly those leveraging Facebook and mobile tools—to help farmers adopt season-specific fertilizer strategies. The authors suggest that this model can be readily extended to other rice-producing regions, including Cambodia and Lao PDR, advancing sustainable nitrogen management across Southeast Asia.
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References
DOI
10.48130/nc-0025-0009
Original Source URL
https://doi.org/10.48130/nc-0025-0009
Funding information
This work was funded by the Australian Centre for International Agricultural Research (ACIAR) SMCN/2014/044 and SLAM/2022/102 projects, and the Young Scientists Fund of the National Natural Science Foundation of China (Grant No. 42207554).
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Nitrogen Cycling is a multidisciplinary platform for communicating advances in fundamental and applied research on the nitrogen cycle. It is dedicated to serving as an innovative, efficient, and professional platform for researchers in the field of nitrogen cycling worldwide to deliver findings from this rapidly expanding field of science.