The research, published in the journal Plant and Soil, was led by Wenjia Yang, Xiaowei Ma, Jun Hou and Bing Cao of Yangtze University and the Beijing Academy of Agriculture and Forestry Sciences. The team set out to test a deceptively simple hypothesis. Controlled-release blended fertilizers, whose polymer coatings meter out nitrogen in step with crop demand, are known to raise yields and nitrogen use efficiency. But when these fertilizers are broadcast on the soil surface, as is common in practice, much of the nitrogen sits far from the densest concentration of rice roots, leaving it vulnerable to volatilization and runoff. Dense planting, the researchers reasoned, could close that gap by expanding the root absorption zone and intercepting nitrogen before it escapes.

To test the idea, the team ran a three-year field experiment with five treatments: a zero-nitrogen control, the conventional farmer’s practice, an optimized nitrogen practice, a single basal application of controlled-release blended fertilizer, and that same fertilizer combined with dense planting. Rather than tracking yield alone, they assembled an unusually complete environmental audit. They measured fluxes of methane and nitrous oxide from the paddies, ammonia volatilization from the floodwater, inorganic nitrogen in the soil and surface water, redox potential, dissolved oxygen, and the abundances of functional genes that govern the microbial nitrogen cycle. They then folded these measurements into greenhouse gas intensity, carbon footprint, and net ecosystem economic benefit calculations.

The yield results were striking. Compared with the farmer’s practice, the controlled-release fertilizer alone increased grain yield by 10 to 30 percent. Adding dense planting pushed yields a further 10 to 15 percent higher, and the mechanism behind the boost was a genuine synergy: the denser stands produced more effective panicles per unit area while each panicle also carried more grains. In other words, the combination did not simply cram more plants into the same space at the expense of individual performance; it lifted both components of the yield equation simultaneously, under a reduced nitrogen input regime.

The environmental accounting was equally revealing. The controlled-release fertilizer cut cumulative methane emissions by 18 to 35 percent, nitrous oxide emissions by 13 to 52 percent, and ammonia volatilization by 40 to 49 percent relative to conventional practice. These reductions trace back to the fertilizer’s core design. By releasing nitrogen gradually, the coating prevents the floodwater from becoming a concentrated nitrogen soup, which suppresses the microbial processes that generate nitrous oxide and the chemical equilibrium that drives ammonia into the air. The smoother nitrogen supply also alters the soil’s redox dynamics and dissolved oxygen profile, conditions that favor methanotrophs, the microbes that consume methane before it reaches the atmosphere.

Dense planting introduced one complication. Relative to the controlled-release fertilizer alone, the combined treatment showed a modest methane rebound of 13 to 14 percent, likely because denser canopies and root systems alter the carbon inputs and gas transport pathways in the flooded soil. The combination also did not further reduce nitrous oxide or ammonia losses beyond what the fertilizer achieved on its own. For a reader scanning only the emission columns, that might look like a step backward.

But the full accounting tells a different story. When emissions are expressed per unit of grain, the combined treatment held greenhouse gas intensity and carbon footprint at levels comparable to the fertilizer alone, because the yield gains diluted the per-kilogram emissions. The modest methane rebound was more than offset by the larger harvest. This yield-driven dilution is a critical insight for climate-smart agriculture: the goal is not simply to minimize absolute emissions from a field, but to minimize the emissions embedded in every bowl of rice produced.

The economics strengthened the case further. The combined treatment boosted net ecosystem economic benefits by 9 to 97 percent compared with the farmer’s practice, a range that reflects both higher grain output and savings on fertilizer and labor, since the controlled-release product requires only a single basal application rather than multiple split dressings. For smallholder farmers in central China, where rice paddies dominate the landscape and nitrogen overuse remains widespread, a practice that simultaneously raises income and cuts pollution addresses the two pressures that most often pull in opposite directions.

The study also connects to a broader scientific conversation about nitrogen-cycling microbes in paddy soils. By measuring the abundances of functional genes involved in nitrification and denitrification, the researchers could link treatment effects on nitrous oxide to shifts in the microbial communities that produce and consume this potent greenhouse gas, which has roughly 273 times the warming power of carbon dioxide over a century. Previous work by the same group and collaborators had shown that root-zone fertilization with controlled-release urea reduces nitrous oxide and ammonia losses under different irrigation regimes, and that combining controlled-release blended fertilizer with densification lowers ammonia volatilization. The new study extends that framework to a full greenhouse gas and carbon footprint assessment over multiple seasons, which is essential because single-year trials can be misleading in variable climates.

The authors conclude that controlled-release blended fertilizer combined with dense planting represents a promising strategy for sustainable rice production in the middle reaches of the Yangtze River, one of China’s most important rice belts. The findings arrive at a moment when rice systems worldwide face intensifying scrutiny: rice cultivation contributes a substantial share of agricultural methane, and global assessments consistently identify nitrogen management as a key lever for reducing the sector’s climate impact. If the yield-and-emissions synergy documented here holds across other rice regions, soil types, and cultivars, the humble act of planting rice a little closer together, with nitrogen delivered on the plant’s schedule rather than the farmer’s, could become one of the most cost-effective climate interventions in staple crop production. The next step, the researchers suggest, is verifying how the approach performs under the wider range of water management practices and soil conditions that define real-world rice farming across Asia.

Subject of Research: Effects of controlled-release fertilizer combined with dense planting on rice yield, greenhouse gas emissions, and carbon footprint

Article Title: Dense planting amplifies yield benefits of controlled-release urea while maintaining low environmental footprint in rice

Article References: Yang, W., Ma, X., Wang, X., Hou, J., Zou, G., & Cao, B. (2026). Dense planting amplifies yield benefits of controlled-release urea while maintaining low environmental footprint in rice. Plant and Soil. https://doi.org/10.1007/s11104-026-09125-y

Image Credits: AI Generated

DOI: 10.1007/s11104-026-09125-y

Keywords: rice, controlled-release fertilizer, dense planting, greenhouse gas emissions, methane, nitrous oxide, ammonia volatilization, carbon footprint, nitrogen use efficiency, paddy field, sustainable agriculture, Yangtze River

The research team worked at the Gao’an Experimental Station in Yichun City, Jiangxi Province, a subtropical monsoon region where early rice is transplanted in late April and harvested in mid-July, and late rice follows from late July to mid-October. During the roughly 150-day fallow period between rice seasons, the researchers grew Chinese milk vetch, a leguminous green manure that fixes atmospheric nitrogen through its symbiotic bacteria. In the spring, this biomass was plowed into the top 20 centimeters of soil along with rice straw and synthetic fertilizer, one week before rice seedlings went into the ground. The experiment built on a long-term field trial running since 2015, giving the soils time to respond to the different management regimes.

The design was elegantly simple in concept. Nine treatments compared winter fallow without fertilizer as a control, conventional full fertilization, and combinations of rice straw, green manure, or both, each crossed with either full or 60 percent reduced synthetic nitrogen rates. Green manure was incorporated at 22,500 kilograms per hectare of fresh weight, while rice straw was applied at 6,000 kilograms per hectare of dry weight. The logic behind pairing the two residues lies in their contrasting chemistry: milk vetch is nitrogen-rich with a low carbon-to-nitrogen ratio and decomposes rapidly, sometimes releasing nutrients faster than rice plants can absorb them, whereas rice straw is carbon-rich, decomposes slowly, and can actually tie up soil nitrogen through microbial immobilization. Blended together, the residues moderate each other’s extremes and release nutrients more steadily across the growing season.

The yield results were striking. Early rice yields ranged from 2,477 kilograms per hectare in the unfertilized control to 6,827 kilograms per hectare under co-incorporation with full fertilization. Compared with conventional fertilization alone, the combined organic practice boosted early rice yields by 18.2 percent at full fertilizer rates and 12.0 percent at reduced rates. Late rice also benefited, with gains of 2.8 and 2.2 percent respectively, and the reduced-fertilizer co-incorporation treatment outperformed the reduced-fertilizer-only control by 13.6 percent. Across the full double-cropping year, the best treatment produced 14,070 kilograms of grain per hectare, the highest of all nine regimes tested.

Nitrogen uptake told a parallel story. Annual aboveground nitrogen uptake in the rice plants reached up to 248 kilograms of nitrogen per hectare in green manure treatments, an increase of up to 31.8 percent over conventional fertilization. Apparent nitrogen use efficiency climbed as high as 57.7 percent in the co-incorporation treatment with reduced fertilizer, compared with just 32.0 percent when rice straw was added to full conventional fertilization. Notably, straw alone actually depressed nitrogen use efficiency, confirming that the high carbon-to-nitrogen residue can leave rice plants short of available nitrogen when microbes outcompete roots for it. The synergy only emerges when the fast-releasing legume and the slow-releasing straw work together.

The environmental findings may matter even more than the agronomic ones. Using sponge-trapping devices and potassium chloride extraction to measure ammonia volatilization, and static chambers coupled with gas chromatography to track nitrous oxide, the team quantified gaseous nitrogen losses across every treatment. Ammonia dominated overwhelmingly, accounting for 97.7 percent of total gaseous losses on average, with annual emissions reaching 241 kilograms of nitrogen per hectare under conventional fertilization. Peaks followed fertilizer applications closely, with late-season fluxes running 2.4 to 4.6 times higher than in early rice, reflecting hotter conditions that accelerate the conversion of ammonium to ammonia gas.

Co-incorporation with reduced fertilizer cut these losses dramatically. Ammonia emissions fell by 10.3 percent at full fertilizer rates and by 30.1 percent when synthetic nitrogen was reduced by 40 percent, relative to conventional practice. Nitrous oxide emissions, though far smaller in magnitude, dropped by 13.6 and 45.5 percent under the same comparisons. Overall gaseous nitrogen losses declined by roughly 12.4 percent with organic amendments at full fertilizer rates and by about 31.7 percent when combined with the 40 percent fertilizer reduction. Expressed per kilogram of grain produced, the yield-scaled emissions intensity was lowest in the co-incorporation treatments, meaning farmers would be producing more rice while releasing less reactive nitrogen per unit of food.

To understand the mechanisms, the researchers applied partial least squares path modeling, a statistical technique that traces how multiple soil and management variables jointly influence emissions. The model explained 84 percent of the variability in ammonia emissions and 89 percent in nitrous oxide emissions. Nitrogen input emerged as the dominant driver of both gases, with standardized path coefficients of 0.94 for ammonia and 0.79 for nitrous oxide. Nitrous oxide was additionally shaped by soil chemistry: available potassium and Olsen-phosphorus exerted negative effects, while soil organic carbon and pH had positive ones. The team also found that organic amendments raised soil organic carbon by up to 22.4 percent and boosted Olsen-phosphorus by nearly 39 percent, improvements that enhance the soil’s buffering capacity and slow the pH shifts that drive ammonia volatilization after urea hydrolysis.

The nitrous oxide story carries a subtle twist. Although incorporating organic residues initially stimulated microbial activity and briefly raised nitrous oxide fluxes, the annual totals remained low—just 1.0 to 1.8 percent of applied nitrogen—because flooded paddy conditions and the oxygen consumed by decomposing residues create a strictly anaerobic environment. Under those conditions, denitrifying microbes push the process to completion, reducing nitrous oxide all the way to harmless dinitrogen gas. In other words, the same waterlogged chemistry that makes paddies productive also gives them a partial safety valve against the most potent greenhouse gas in the nitrogen cycle.

The implications extend well beyond Jiangxi. Intensive fertilizer use has driven ammonia emissions up 78 percent and nitrous oxide emissions up 46 percent in heavily fertilized systems, contributing to smog formation, acid rain, biodiversity loss, and climate change, while less than half of applied fertilizer nitrogen typically ends up in the crop. This study demonstrates that a practice already widely adopted across southern China—plowing in milk vetch grown during the winter fallow alongside returned rice straw—can replace a meaningful share of synthetic nitrogen without sacrificing yield, and can even improve it. For a staple crop that must expand production by roughly 10 million tons annually to meet future demand, the message is compelling: the path to sustainable rice intensification may already be growing in the paddies during the off-season, waiting to be turned under come spring.

Subject of Research: Effects of co-incorporating green manure and rice straw with reduced synthetic fertilizer on rice yield and gaseous nitrogen losses in double-cropped paddy fields

Article Title: Co-incorporation of green manure and rice straw with reduced synthetic fertilizer benefits rice yield while decreasing gaseous N losses in double-cropped rice fields

Article References: Wan, L., Ma, T., Liu, H., Chen, X., Qin, W., Li, G., Xie, J., Ge, T., & Liu, J. (2026). Co-incorporation of green manure and rice straw with reduced synthetic fertilizer benefits rice yield while decreasing gaseous N losses in double-cropped rice fields. Journal of Agriculture and Food Research, 31, Article 103345. https://doi.org/10.1016/j.jafr.2026.103345

Image Credits: AI Generated

DOI: 10.1016/j.jafr.2026.103345

Keywords: rice, green manure, milk vetch, rice straw, nitrogen use efficiency, ammonia volatilization, nitrous oxide, paddy soil, double-cropped rice, fertilizer reduction, soil organic carbon, sustainable agriculture

The research team, led by Amanda S. Giroto, set out to build a controlled-release urea fertilizer from carboxymethyl cellulose, or CMC, a renewable, low-toxicity derivative of cellulose that is abundant, highly hydrophilic, and capable of forming films and hydrogels. CMC has long been viewed as a promising scaffold for agricultural delivery systems, but it carries a fundamental weakness: its affinity for water is so strong that, unless the polymer network is stabilized, it swells excessively or dissolves outright, releasing its payload by disintegration rather than by regulated diffusion. The Brazilian group tackled this problem with a dual strategy, crosslinking the polymer chains with citric acid, a cheap and food-safe polycarboxylic acid that forms ester bonds with cellulose hydroxyl groups, and dispersing bamboo-derived biochar throughout the matrix as a physical barrier and adsorptive phase.

The experimental design was deliberately systematic. A 2 percent aqueous CMC solution was prepared, urea was added at 50 percent of the polymer mass, and biochar was incorporated at a fixed 1 percent of total composite mass. Citric acid was then introduced at four levels, 0, 10, 20, and 30 percent by weight relative to CMC, and the mixtures were heated to 80 degrees Celsius for two hours to drive the crosslinking reaction before being cast into self-supporting films and dried. The resulting formulations, labeled CMC/U, CMC/U/BC/CA0, CA10, CA20, and CA30, were probed with X-ray diffraction, infrared spectroscopy, electron microscopy, and thermal analysis, then subjected to swelling tests, water-retention trials in sandy soil, aqueous urea-release experiments, and a 42-day soil incubation tracking ammonia volatilization and ammonium formation.

The structural characterization revealed formulation-dependent changes in the crystalline organization and thermal environment of urea within the matrices. Electron microscopy showed that the non-crosslinked material possessed a smooth surface with well-defined urea crystals, while biochar incorporation produced a rougher, more heterogeneous morphology dotted with porous features. The 10 percent citric acid formulation displayed a relatively cohesive structure, the 20 percent version was the most compact and homogeneous, and the 30 percent sample turned granular and fragmented. Thermal analysis showed that the decomposition temperature of the polymer backbone shifted progressively upward with increasing citric acid content, reaching roughly 284 degrees Celsius at the highest loading, evidence of a more thermally stabilized network. Differential scanning calorimetry, meanwhile, showed that the sharp melting endotherm of pure urea at about 136 degrees Celsius was broadened, reduced, or suppressed in the composites, indicating that urea molecules were dispersed and interacting within the polymeric network rather than sitting as free crystalline granules.

The swelling experiments delivered the study’s most striking numbers. Without citric acid, the composites rapidly lost their structural integrity in water, forming a viscous gelatinous mass that could not even be weighed reliably. In contrast, all crosslinked formulations remained intact throughout immersion, and the 10 percent citric acid composite swelled to approximately 7500 percent of its dry mass within an hour, compared with about 4800 percent at 20 percent crosslinker and 2800 percent at 30 percent. Counterintuitively, the highest swelling did not translate into the fastest nutrient release. In water, pristine urea dissolved almost instantaneously, releasing its entire payload within the first four hours, whereas the CA10 composite had surrendered only about 18 percent of its urea at that point and roughly 80 percent by the end of the eight-day test. The 20 and 30 percent formulations released faster, with the CA20 sample reaching up to 90 percent.

This non-linear relationship between crosslinker content and release behavior is one of the paper’s central insights. The authors argue that beyond an optimal point, additional citric acid restricts polymer-chain mobility, increasing matrix rigidity and morphological heterogeneity in ways that can open preferential diffusion pathways and accelerate transport rather than slow it. Kinetic modeling reinforced the complexity of the mechanism. All composites fitted the Higuchi diffusion model well, but the Peppas–Sahlin analysis showed that urea release involved simultaneous diffusional transport and polymer-chain relaxation, with the relaxational contribution growing from roughly a quarter to nearly 40 percent of the modeled release over the first eight hours. The researchers are careful to note that the data do not support describing the process as purely Fickian diffusion; instead, release emerges from the coupled interplay of hydration, structural reorganization, and solute transport.

Water retention, a critical co-benefit for drought-prone agriculture, also improved. In sandy soil amended with the composites and held at 40 degrees Celsius, the non-crosslinked biochar formulation retained about 59 percent of its initial water after 120 hours, compared with 47 percent for unamended sand, although this difference fell short of statistical significance. At 24 hours, significant differences among treatments were detected, and the biochar-containing matrices showed a consistent tendency toward better long-term moisture preservation, a property the authors attribute to the hydrogel’s water-holding capacity combined with biochar’s porosity.

Perhaps the most consequential results came from the soil incubation. Over 42 days under conditions deliberately chosen to accelerate urea hydrolysis and nitrogen loss, every composite reduced measured ammonia volatilization relative to pure urea. Pure urea lost the most nitrogen as ammonia, 3.74 milligrams, while the uncrosslinked CMC/urea composite lost the least, 2.29 milligrams, a statistically significant reduction. Ammonium dynamics shifted as well: in the first week, the composites sustained higher exchangeable ammonium pools than pristine urea, suggesting that the matrices kept nitrogen in a plant-available mineral form for longer rather than letting it escape as gas. A partial nitrogen recovery accounting, based on the two measured pools, ranged from 56.4 to 72.4 percent of the applied nitrogen, with the remainder classified conservatively as unaccounted because nitrate and matrix-associated nitrogen were not directly quantified.

The practical implications are considerable. Because CMC, citric acid, and biochar are all inexpensive, renewable, and biodegradable, the proposed system sidesteps the central criticism of commercial controlled-release fertilizers, many of which rely on non-biodegradable synthetic coatings that persist in soil. The fabrication route is equally appealing: a simple aqueous process, a single heating step at 80 degrees Celsius, and air drying, with no exotic reagents or energy-intensive procedures. The authors frame the work as demonstrating that one biodegradable polymer matrix, properly architected, can efficiently regulate nutrient release through a simple, scalable, and sustainable strategy for advanced nitrogen fertilizers.

The deeper lesson, however, is about optimization philosophy. Increasing crosslinker content did not monotonically improve performance, and the best formulation was the one that balanced swelling, structural integrity, and diffusion-pathway continuity rather than the most heavily crosslinked one. As agriculture confronts the twin pressures of feeding a growing population and cutting the nitrogen pollution that warms the climate and degrades waterways, studies like this one suggest that the smartest fertilizers of the coming decade may be built not from petrochemical shells but from engineered plant polysaccharides, kitchen-safe acids, and charcoal, tuned with precision at the molecular scale.

Subject of Research: Development of citric acid-crosslinked carboxymethyl cellulose and biochar composites for controlled-release urea fertilizer

Article Title: Controlled urea release from CMC-based composites: effects of citric acid crosslinking and biochar incorporation

Article References: Giroto, A. S., Prado, T. R., Yashima, A., Valle, S. F., Alves, B. L., & Gonçalves, M. (2026). Controlled urea release from CMC-based composites: effects of citric acid crosslinking and biochar incorporation. Polymer Bulletin, 83(11), Article 636. https://doi.org/10.1007/s00289-026-06685-y

Image Credits: AI Generated

DOI: 10.1007/s00289-026-06685-y

Keywords: controlled-release fertilizer, carboxymethyl cellulose, urea, biochar, citric acid crosslinking, nitrogen use efficiency, ammonia volatilization, biodegradable polymer, hydrogel, soil water retention, release kinetics, sustainable agriculture