Transforming agricultural practices for sustainable food production and environmental protection
Global nitrogen fertilizer consumption by China
Average nitrogen use efficiency in Chinese farms
Nitrogen lost to the environment
It's a paradox of modern farming: the very substance that helps feed a nation also threatens its environment. Imagine if for every 100 bags of fertilizer applied to crops, only 16-18 actually reached the plants. The rest would vanish into thin air or wash away into waterways. This isn't hypothetical—it's the reality of nitrogen management in China's intensive wheat-maize farming system, which produces more than half of China's food 1 .
In 2005, China alone accounted for a staggering 38% of global nitrogen fertilizer consumption 1 4 . Yet the average on-farm nitrogen recovery efficiency—the measure of how much fertilizer crops actually use—stood at just 16-18% 1 4 . This inefficiency has created a cascade of environmental challenges, from algal-choked waterways to climate-warming gas emissions.
The good news? Science is delivering solutions. Recent research reveals how innovative approaches can simultaneously boost crop yields, save farmers money, and protect our environment. This is the story of China's journey toward sustainable nitrogen management—a crucial shift that could transform one of the world's most important agricultural systems.
Nitrogen is essential for life. It's a fundamental building block of proteins and chlorophyll, the compound that gives plants their green color and enables photosynthesis. But in agriculture, the relationship with nitrogen has become complicated.
While research trials in China show nitrogen recovery efficiency can reach 26-28%, the actual efficiency in farmers' fields is much lower—just 16-18% 1 . This means that of the approximately 500-600 kilograms of nitrogen fertilizer that farmers typically apply per hectare each year for the wheat-maize rotation system, only a small fraction actually feeds the crops 1 .
The rest goes elsewhere. Isotope studies reveal that in intensive wheat-maize systems, only about 25% of applied nitrogen fertilizer is absorbed by crops, while 25-45% accumulates in soil and a troubling 30-50% is lost to the environment 1 . This waste comes with significant costs—both economic and environmental.
The numbers reveal a striking efficiency gap. Chinese on-farm nitrogen efficiency is less than half that achieved in global research trials and significantly lower than on-farm efficiency in the United States 1 . This gap represents both a challenge and an opportunity.
The most obvious problem is simply applying too much nitrogen. Typical farmer application rates often exceed 500 kg nitrogen per hectare annually for the wheat-maize system, approaching 600 kg in some regions 1 . Meanwhile, research shows the economically optimal rate is only 130-160 kg nitrogen per hectare per crop 1 . This means many farmers are applying two to three times more fertilizer than needed for optimal yields.
Farmers often focus solely on chemical fertilizers while ignoring the significant contributions from other sources. The soil itself contains nitrogen, and environmental processes like atmospheric deposition add more. When these sources aren't accounted for, excessive application becomes inevitable.
Crops have specific nitrogen needs at different growth stages. Applying fertilizer without considering these needs creates a mismatch—the plant may be hungry when little nitrogen is available, or overwhelmed when it doesn't need much. This poor synchrony between crop demand and nitrogen supply significantly reduces efficiency.
When farming practices don't fully realize a crop's genetic potential, the plants can't use available nitrogen efficiently. Achieving high yields and high nitrogen efficiency must go hand-in-hand—we can't have one without the other.
The consequences extend far beyond farm economics. Excess nitrogen pollutes waterways, causing algal blooms that deplete oxygen and create "dead zones" where aquatic life can't survive. It also contributes to air pollution and greenhouse gas emissions, particularly nitrous oxide—a climate-warming gas 300 times more potent than carbon dioxide 5 .
The scientific community has responded to this challenge with a suite of innovative strategies. The core principle is simple but powerful: managing various nitrogen sources to limit total applied nitrogen, while spatially and temporally matching nitrogen supply with crop demand 1 .
At the heart of modern nitrogen management is the "4R" concept—applying the Right source of fertilizer at the Right rate, Right time, and Right place. This framework, while simple in principle, requires sophisticated understanding of crop nutrition, soil science, and agronomy.
Research demonstrates that significantly reducing nitrogen application from farmer practice levels—while maintaining proper timing and placement—can actually increase yields while reducing environmental impact. One eight-season field study showed that optimized nitrogen treatment increased maize yield by 5.5-7.3% and wheat yield by 3.2-6.2% compared to farmer practices, despite using far less fertilizer 2 .
Controlled-release urea represents a technological breakthrough. These specially formulated fertilizers release nitrogen gradually, aligning with crop needs. Studies show they can achieve higher yields with 20% less nitrogen input 2 . Though more expensive upfront, their efficiency can make them economically viable.
Combining chemical fertilizers with organic sources like crop residues or properly managed manure creates a more balanced nutrient supply while improving soil health. One study found that substituting 20% of synthetic nutrients with duck manure reduced nitrogen runoff while maintaining yields 2 .
Water and nitrogen management are deeply connected. Subsurface drip irrigation systems deliver water and dissolved nutrients directly to plant root zones, dramatically improving efficiency. Research shows this approach can increase maize yields by 16% while saving 25% of nitrogen fertilizer and reducing irrigation water use by about 55% 8 .
To understand how these strategies perform in real-world conditions, let's examine a comprehensive field study conducted in China's Nansi Lake watershed—an important region for the south-to-north water transfer project.
Researchers designed a meticulous experiment running for eight consecutive growing seasons from 2009 to 2013 2 . They compared six different management approaches:
No nitrogen fertilizer, only phosphorus and potassium
Farmer practice (high nitrogen: 345 kg/ha for maize, 240 kg/ha for wheat)
Optimized NPK (180 kg N/ha for both crops)
Controlled-release urea (20% less nitrogen than OPT)
Duck manure supplement (20% of OPT nutrients replaced by manure)
Straw returning (OPT plus crop residues)
Each treatment was replicated across multiple plots with careful monitoring of crop yields, nitrogen uptake, and—crucially—nitrogen losses through runoff and leaching into water systems.
The findings were striking. The controlled-release urea (CRU) treatment achieved the highest nitrogen use efficiency while reducing environmental impact most effectively 2 . Compared to farmer practices, CRU reduced nitrogen loss through leachate by 39.5-45.5% and runoff nitrogen loss by 31.9-35.9% 2 .
Perhaps most remarkably, the optimized nitrogen treatment (OPT)—with significantly less fertilizer than farmer practice—increased yields for both maize (5.5-7.3%) and wheat (3.2-6.2%) 2 . This powerfully demonstrates that more fertilizer doesn't necessarily mean more food—smarter management does.
The study also revealed that synthetic nitrogen input correlated significantly and positively with runoff and leachate nitrogen losses, confirming it as a dominant factor driving water pollution 2 .
Optimized nitrogen application with controlled-release urea can increase yields while reducing environmental nitrogen losses by 30-45%.
China's nitrogen challenge reflects a broader global issue. Worldwide, approximately 80% of reactive nitrogen is lost to the environment rather than productively used 6 . Scientists estimate this waste represents up to $300 billion in lost fertilizer value annually 6 .
The United Nations has recognized sustainable nitrogen management as crucial for achieving most of its Sustainable Development Goals, from zero hunger to clean water and climate action 6 . An international team of researchers recently identified 150 "win-win" measures that could significantly reduce nitrogen pollution while saving costs across multiple industries 6 .
Better fertilizer storage and precision application techniques
Using cover crops to retain nitrogen in soils between growing seasons
Recovering nitrogen from sewage and food waste for reuse in agriculture
"Improving nitrogen management offers a remarkable opportunity to not only enhance environmental health but also strengthen the global economy. The key lies in adopting an integrated approach across the entire nitrogen cycle."
The path forward for China's wheat-maize systems—and global agriculture more broadly—lies in working smarter, not harder. The research is clear: we can maintain high crop yields while dramatically reducing nitrogen fertilizer use through science-based management approaches.
Matching nitrogen supply to crop demand in both time and space
Using innovations like controlled-release fertilizers and precision irrigation
Combining organic and synthetic nutrient sources for balanced nutrition
The transformation of China's nitrogen management represents more than just improved farming practices—it's a critical step toward building sustainable food systems that can nourish both people and the planet for generations to come. The science has shown us the way forward; now comes the work of bringing these solutions to every field.